Quality evaluation of ice cream produced
in Khartoum State, Sudan
By
Zeinab Khalil Omer Khater
(B.Sc. Food Science and Technology)
Faculty of agricultural sciences (Honours) University of Alzaiem Alazhari 2002
Supervisor:
Dr: Osman Ali Osman El Owni
A thesis submitted in partial fulfilment for the degree of Master of Science in Dairy production and Technology
Department of Dairy Production Faculty of Animal Production
University of Khartoum
November 2005
To my beloved family and specially friends Acknowledgements
At the start and end I thank Allah for giving me the power and patience to come up with this research.
I am sincerely grateful to Dr. Osman Ali Osman El owni for his supervison and helpful advices during the study period.
I am particularly indebted and grate full to Dr.
Ibtisam El Yas Mohamed El Zubeir, Head Department of
Dairy production, Faculty of Animal Production.
My thanks are extended to all the staff members of the Faculty of Animal production, University of Khartoum.
My deepest thanks should be extended to my family for their encouragement and financial support during the study.
Thanks are also extended to every body whom I did not mention.
Table of contents
Contents Page
Dedication ………………………………………………………………... i
Acknowledgements ……………………..………………………………... ii
Table of contents ……………………………………..…………………... iii
List of tables ……………………………………………………………... vii
List of figures ………………...…………………………………………... viii
Abstract ……………………………………………………………...... ix
Arabic abstract …………………………………………………………… xi
CHAPTER ONE: INTRODUCTION …………………………………. 1
CHAPTER TWO: LITERATURE REVIEW ………………………... 3
2.1 Definition of ice cream ………………………………….…………… 3
2.2 History of ice cream ………………………………….………………. 3
2.3 Nutritive value of ice cream ………………………………….……… 5
2.4 Ice cream ingredients ………………………………….……………... 5
2.4.1 Milk fat ………………………………….…………………………. 7
2.4.2 Milk solids non fat ………………………………….……………… 8
2.4.3 Sugar and sweetening agents ………………………………………. 9
2.4.4 Stabilizing agents ………………………………….……………….. 10 2.4.5 Emulsifying agents ………………………………………………… 11 2.4.6 Flavoring materials ………………………………….……………... 12 2.4.7 Coloring materials ………………………………….……………… 13 2.4.8 Air ………………………………….………………………………. 14 2.5 Factors affecting of manufacturing procedures ……………………… 14 2.5.1 Mixing of ingredients ………………………………….…………... 14 2.5.2 Heat treatment ………………………………….…………………... 15 2.5.3 Homogenization ………………………………….………………… 16 2.5.4 Cooling ………………………………….…………………………. 18 2.5.5 Aging ………………………………….…………………………… 19 2.5.6 Freezing ………………………………….………………………… 19 2.5.7 Overrun ………………………………….…………………………. 20 2.5.8 Hardness ………………………………….………………………... 21 2.5.9 Packaging ………………………………….……………………….. 21 2.5.10 Storage and distribution ………………………………….……….. 23 2.6 Defects of ice cream ………………………………….……………… 23 2.6.1 Body and texture defects ………………………………….……….. 23 2.6.2 Flavor defects ………………………………….…………………… 25 2.6.3 Shrinkage defects ………………………………….……………….. 26 2.6.4 Color defects ………………………………….……………………. 26 2.7 Microbiology of ice cream ingredients ………………………………. 27 2.8 Potential microbiological hazards associated with ice cream ………... 28 2.9 Major diseases transmitted through ice cream ………………………. 30 CHAPTER THREE: MATERIALS AND METHODS ……………… 34 3.1 Ice cream sample collection ………………………………….………. 34 3.2 Chemical analyses of ice cream ……………………………………… 34 3.2.1 Determination of fat content ……………………………………….. 35 3.2.2 Determination of protein content …………………………………... 35 3.2.3 Determination of total solids content ………………………………. 36 3.2.4 Determination of ash content ………………………………………. 37 3.2.5 Determination of total sugars content ……………………………… 38 3.2.5.1 Determination of reducing sugars content ……………………….. 39 3.3 Microbiological examination of ice cream …………………………... 39 3.3.1 Sterilization of equipment and media ……………………………… 39 3.3.2 Microbiological media ……………………………………………... 40 3.3.2.1 Standard plate count (SPC) ………………………………………. 40 3.3.2.2 Mac Conkey Agar ……………………………………………….. 40 3.3.2.3 Yeast extract agar ………………………………………………... 41 3.3.3 Plating, enumeration and counting of bacteria …………………….. 41 3.3.3.1 Preparation of sample dilution …………………………………… 41 3.3.3.2 Enumeration of total bacteria …………………………………….. 41 3.3.3.3 Enumeration of coliform bacteria ………………………………... 42 3.3.3.4 Enumeration of psychrotrophic bacteria …………………………. 42 3.3.3.5 Enumeration of Yeast counts …………………………………….. 43 3.4 Sensory evaluation …………………………………………………… 43 3.5 Statistical analysis …………………………………………………… 43 CHAPTER FOUR: RESULTS AND DISCUSSION …………………. 44
4.1 Flavors and chemical composition of ice cream ……………………... 44
4.2 The microbial count of ice cream ……………………………………. 48
4.3 Sensory characteristics of ice cream …………………………………. 57
CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS . 64
5.1 Conclusions ………………………………….………………………. 64 5.2 Recommendations …………………………………………………… 65
REFERENCES ………………………………….……………………… 66 List of tables
Table Page (2-1): Hazards and typical control in the production of ice 31 cream . (4-1): Average chemical composition of ice cream samples from machines and looli factory 45 ……………………………………….. (4-2): Effect of type of flavor on chemical composition of ice cream 47 ………………………………….………………………….. (4-3): Chemical composition of flavored ice cream from machines producers 49 ………………………………….……………………… (4-4): Chemical composition of flavored ice cream from Looli factory 50 ………………………………….………………………… (4-5): Microbial quality of ice cream samples from machines and Looli factory 51 ………………………………….…………………... (4-6): Average microbial quality of flavored ice cream 53 …………. (4-7): Average microbial quality of flavored from ice cream machines 55 …….………………………………….………………… (4-8): Average microbial quality of flavored ice cream samples from Looli factory 56 ………………………………….…………….. (4-9): Sensory characteristics of ice cream samples from Looli factory and ice Machines 58 ………………………………………… (4-10): Sensory characteristics of flavored ice cream 60 ……………. (4-11): Flavor and sensory characteristics of ice cream from machines 62 ………………………………….………………………. (4-12): Flavor and sensory characteristics of ice cream from
Looli factory 63 ……………………………………………………………. List of figures
Figure Page (2.1): Soft serve ice cream is the perfect frozen dessert after any meal 6 ………………………………….…………………………… (2-2): Ice cream processing adopted from the University of
Guelph (Goff, 1998) 24 ………………………………….…………... (2-3): Large ice ream plant for production of 5000-10000 1/h of various types of ice cream 33 ………………………………………...
Abstract
This study was conducted during the period from September 2003 to March 2004, in the Laboratory of Dairy Production, Faculty of Animal Production U. of Kh. to compare the chemical, microbial and sensory characteristics of different types of ice cream. Hundred samples were collected from which 60 were from ice cream machines and 40 were from Looli factory in Khartoum State. The results revealed a highly significant differences (P<0.001) in all chemical components except protein and sucrose. The results showed non significant differences (P>0.05) in all chemical components due to flavor except total solids. There was non significant differences (P>0.05) between machines and Looli ice cream with respect to type of flavor in all chemical components except total solids. The microbiological examination showed non significant differences (P>0.05) in yeast count, coliform and psycrotrophic bacterial counts in both machines and Looli ice cream except total bacterial counts. Yeast count, coliform and psychrotrophic count were highest in Looli samples, while total bacterial count was highest in machine samples. The results indicated highly significant differences (P<0.01) in coliform and yeast counts due to type of flavor. But there were non significant differences (P>0.05) in total bacterial and psychrotrophic counts. The results between machines and Looli factory made by flavor showed non significant differences (P>0.05) in all microbiological tests except in total bacterial counts. According to results of the panel tests for sensory evaluation, all machines and Looli samples showed highly significant differences
(P<0.001) in texture, flavor, taste and overall acceptability, while color presented non significant differences (P>0.05). The sensory characteristics of flavor postulated non significant differences
(P>0.05) in all sensory tests except in flavor. The difference in results of machines and Looli made by flavor indicated non significant differences (P>0.05) in color, taste and overall acceptability, whereas texture and flavor showed significant differences. ﻣﻠﺨﺺ اﻷﻃﺮوﺣﺔ
أﺟﺮﻳﺖ هﺬﻩ اﻟﺪراﺳﺔ ﻓﻲ اﻟﻔﺘﺮة ﻣﺎ ﺑﻴﻦ ﺳﺒﺘﻤﺒﺮ 2003م إﻟﻰ ﻣﺎرس 2004م ﻓ ﻲ ﻣﻌﻤ ﻞ إﻧﺘ ﺎج اﻷﻟﺒ ﺎن، آﻠﻴ ﺔ اﻹﻧﺘ ﺎج اﻟﺤﻴ ﻮاﻧﻰ ج . اﻟﺨﺮﻃ ﻮم ﻟﻤﻘﺎرﻧ ﺔ اﻟﺘﺮآﻴ ﺐ اﻟﻜﻴﻤﻴ ﺎﺋﻰ ، اﻟﺨ ﻮاص اﻟﻤﻴﻜﺮوﺑﻴﻮﻟﻮﺟﻴ ﺔ واﻟﺨ ﻮاص اﻟﺤ ﺴﻴﺔ ﻷﻧ ﻮاع ﻣﺨﺘﻠﻔ ﺔ ﻣ ﻦ اﻷﻳ ﺴﻜﺮﻳﻢ. ﺗ ﻢ ﺟﻤ ﻊ ﻣﺎﺋ ﺔ ﻋﻴﻨ ﺔ، 60 ﻣﻨﻬﺎ ﻣﻦ ﻣﺎآﻴﻨﺎت اﻷﻳﺴﻜﺮﻳﻢ و40 ﻣﻦ ﺷﺮآﺔ ﻟﻮﻟﻲ ﻓﻲ وﻻﻳﺔ اﻟﺨﺮﻃﻮم. أوﺿ ﺤﺖ ﻧﺘ ﺎﺋﺞ اﻟﻤﻨﺘﺠ ﻴﻦ (ﻣﺎآﻴﻨ ﺎت وﺷ ﺮآﺔ ﻟ ﻮﻟﻰ) اﻟﺘ ﺄﺛﻴﺮ اﻟﻤﻌﻨ ﻮي اﻟﻜﺒﻴ ﺮ(P<0.001) ﻋﻠ ﻰ ﺟﻤﻴ ﻊ اﻟﻤﻜﻮﻧ ﺎت اﻟﻜﻴﻤﻴﺎﺋﻴ ﺔ ﻣ ﺎ ﻋ ﺪا اﻟﺒ ﺮوﺗﻴﻦ واﻟ ﺴﻜﺮوز. أوﺿ ﺤﺖ اﻟﻨﺘ ﺎﺋﺞ أﻧ ﻪ ﻟ ﻴﺲ هﻨﺎﻟ ﻚ ﺗ ﺄ ﺛ ﻴ ﺮ اً ﻣﻌﻨﻮﻳ ﺎً (P>0.05) ﻟﻠﻨﻜﻬ ﺔ اﻟﻤ ﻀﺎﻓﺔ ﻋﻠ ﻲ ﺟﻤﻴ ﻊ اﻟﻤﻜﻮﻧ ﺎت
اﻟﻜﻴﻤﻴﺎﺋﻴﺔ ﻋﺪا اﻟﺠﻮاﻣﺪ اﻟﻜﻠﻴﺔ اﻟﺼﻠﺒﺔ . آﻤﺎ أﻧﻪ ﻟﻴﺲ هﻨﺎﻟﻚ ﺗ ﺄ ﺛ ﻴ ﺮ اً ﻣﻌﻨ ﻮي (P>0.05]]]]]) ﺑ ﻴﻦ آ ﻞ ﻣﻦ اﻟﻤﻨﺘﺠﻴﻦ واﻟﻨﻜﻬﺔ اﻟﻤﻀﺎﻓﺔ ﻋﻦ ﺟﻤﻴﻊ اﻟﻤﻜﻮﻧﺎت اﻟﻜﻴﻤﻴﺎﺋﻴﺔ ﻋﺪا اﻟﺠﻮاﻣﺪ اﻟﻜﻠﻴﺔ اﻟﺼﻠﺒﺔ. أوﺿﺤﺖ اﻻﺧﺘﺒﺎرات اﻟﻤﻴﻜﺮوﺑﻴﻮﻟﻮﺟﻴﺔ اﻧﻪ ﻟﻴﺲ هﻨﺎﻟﻚ ﺗﺄﺛﻴﺮاً ﻣﻌﻨﻮﻳﺎً ﻋﻠﻰ اﻟﻌﺪ اﻟﻜﻠ ﻲ
ﻟﻠﺨﻤ ﺎﺋﺮ ، ﺑﻜﺘﻴﺮﻳ ﺎ اﻟﻘﻮﻟ ﻮن Bacteria coliform واﻟﺒﻜﺘﺮﻳ ﺎ اﻟﻤﺤﺒ ﺔ ﻟﻠﺒ ﺮودة Psychrotrophic bacteria ﻓﻲ ﺁﻳﺴﻜﺮﻳﻢ اﻟﻤﺎآﻴﻨﺎت وﺷﺮآﺔ ﻟ ﻮﻟﻰ ﻣ ﻌ ﺎً ﻣ ﺎ ﻋ ﺪا اﻟﻌ ﺪد اﻟﻜﻠ ﻲ
ﻟﻠﺒﻜﺘﺮﻳﺎ P<0.001) Total bacteria count). ﺣﻴ ﺚ وﺟ ﺪ أن أﻋﻠ ﻰ ﻋ ﺪد آﻠ ﻲ ﻣ ﻦ اﻟﺨﻤ ﺎﺋﺮ، ﺑﻜﺘﺮﻳﺎ اﻟﻘﻮﻟﻮن واﻟﺒﻜﺘﺮﻳﺎ اﻟﻤﺤﺒﺔ ﻟﻠﺒ ﺮودة ﻓ ﻲ ﻋﻴﻨ ﺎت ﻟ ﻮﻟﻲ، ﺑﻴﻨﻤ ﺎ أﻋﻠ ﻰ ﻋ ﺪد آﻠ ﻲ ﻟﻠﺒﻜﺘﺮﻳ ﺎ ﻓ ﻲ ﻋﻴﻨﺎت اﻟﻤﺎآﻴﻨﺎت . آﻤﺎ أﺷﺎرت اﻟﻨﺘﺎﺋﺞ اﻟ ﻲ وﺟ ﻮد ﺗ ﺄﺛﻴﺮ ﻣﻌﻨ ﻮي (P<0.01) ﻟﻠﻨﻜﻬ ﺔ ﻋﻠ ﻰ اﻟﻌ ﺪد اﻟﻜﻠ ﻲ ﻟﺒﻜﺘﺮﻳ ﺎ اﻟﻘﻮﻟ ﻮن واﻋ ﺪاد اﻟﺨﻤ ﺎﺋﺮ، ﺑﻴﻨﻤ ﺎ ﻻﻳﻮﺟ ﺪ ﻓ ﺮق ﻣﻌﻨ ﻮئ ﻟﻠﻌ ﺪد اﻟﻜﻠ ﻲ ﻟﻠﺒﻜﺘﺮﻳ ﺎ واﻟﺒﻜﺘﺮﻳ ﺎ اﻟﻤﺤﺒ ﺔ ﻟﻠﺒ ﺮودة. ﻟ ﻢ ﺗﺒ ﻴﻦ اﻟﻨﺘ ﺎﺋﺞ وﺟ ﻮد ﻓ ﺮق ﻣﻌﻨ ﻮي (P>0.05) ﺑ ﻴﻦ اﻟﻤﻨﺘﺠ ﻴﻦ واﻟﻨﻜﻬﺔ ﻋﻠﻰ ﺟﻤﻴ ﻊ اﻻﺧﺘﺒ ﺎرات اﻟﻤﻴﻜﺮوﺑﻴﻮﻟﻮﺟﻴ ﺔ ﻋ ﺪا اﻟﻌ ﺪد اﻟﻜﻠ ﻲ ﻟﻠﺒﻜﺘﺮﻳ ﺎ . أوﺿ ﺤﺖ ﻧﺘ ﺎﺋﺞ اﺧﺘﺒ ﺎرات اﻟﺘ ﺬوق ﻟﻠﺘﻘﻴ ﻴﻢ اﻟﺤ ﺴﻲ ﺑ ﺎن ﺟﻤﻴ ﻊ ﻋﻴﻨ ﺎت اﻟﻤﻨﺘﺠ ﻴﻦ ﻟﻬ ﺎ ﺗ ﺄﺛﻴﺮ ﻣﻌﻨ ﻮي آﺒﻴﺮ(P<0.001) ﻓﻲ اﻟﻘﻮام، اﻟﻨﻜﻬﺔ، اﻟﻄﻌﻢ واﻟﻘﺒﻮل اﻟﻌﺎم، ﺑﻴﻨﻤ ﺎ ﻟ ﻢ ﻳﺒ ﻴﻦ اﻟﻠ ﻮن ﺗ ﺄﺛﻴﺮا ﻣﻌﻨﻮﻳ ﺎ . واوﺿﺤﺖ اﻟﺨﺼﺎﺋﺺ اﻟﺤﺴﻴﺔ ﻟﻠﻨﻜﻬﺔ ﻋﺪم اﻟﺘﺄﺛﻴﺮ اﻟﻤﻌﻨﻮي ﻋﻠﻰ ﺟﻤﻴﻊ اﻻﺧﺘﺒﺎرات اﻟﺤﺴﻴﺔ ﻋ ﺪا اﻟﻨﻜﻬ ﺔ (P<0.05). أﺷ ﺎرت اﻟﻨﺘ ﺎﺋﺞ ﺑ ﺎن اﺧ ﺘﻼف ا ﻟﻤﻨﺘﺠ ﻴﻦ ﻓ ﻲ اﻟﻨﻜﻬ ﺔ ﻟ ﻴﺲ ﻟﻬ ﺎ ﺗ ﺄﺛﻴﺮ ﻣﻌﻨ ﻮ ي ﻋﻠﻰ اﻟﻠﻮن، اﻟﻄﻌﻢ واﻟﻘﺒﻮل اﻟﻌ ﺎم، آﻤ ﺎ اوﺿ ﺤﺖ اﻟﻨﺘ ﺎﺋﺞ ان اﻟﻘ ﻮام واﻟﻨﻜﻬ ﺔ ﻟﻬﻤ ﺎ ﺗ ﺄﺛﻴﺮا ﻣﻌﻨﻮﻳ ﺎ .(p<0.05) CHAPTER ONE
INTRODUCTION
Frozen desserts are among the most popular desserts eaten in or out the home. These include ice cream, ices, sherbets and mousses
(Peckham, 1974).
Ice cream represents a congealed dairy produced by freezing pasteurized mixture of milk, cream, milk solids other than fat, sugars, emulsifiers and stabilizers (FEHD, 2003). Products of dairy origin are the main ingredients of ice cream. These include whole milk, skimmed milk, cream, frozen cream, condensed milk products and milk solid. Other ingredients include flavoring matters and water
(FEHD, 2003).
Ice cream is a popular dairy product throughout the world. As a result, its production and consumption are rapidly increasing and the substantial part of milk produced in many countries is being utilized for the manufacture of frozen dessert (Elahi et al., 2002).
The world is faced with a problem of food shortage, so milk products are considered as a partial solution for this problem in developing countries. However these products are vulnerable to spoil by certain microorganism, some of which are beneficial and others are harmful to human beings (Esmail, 1997). All types of ice cream, whether machine, canned, car ice cream or “Dandorma” are present in
Sudan. However the locally made type of ices, which is called
“Dandorma”, is well known in urban areas in Sudan, but unfortunately it is not checked by public health authorities. So a hazard of being contaminated is greatest (Esmail, 1997).
The richness in nutritive constituents of ice cream has been realized by all; however some hazards may lies between production and handling. So great difficulties with regard to chemical and microbiological quality of ice cream (Bigalke and Chappel, 1984).
Quality and price are two major factors in determining not only the volume of current business but also the future of the entire ice cream industry in Sudan.
The objective of this study is to evaluate; including some sensory measures, the following:
1. Chemical composition of ice cream offered for sale in the three
towns of Khartoum State.
2. Microbiological quality of ice cream produced in Khartoum
State.
CHAPTER TWO
LITERATURE REVIEW
2.1 Definition of ice cream: Ice cream may be defined as a food prepared with one or more milk products, sweetened with one or more optional saccharine ingredients and contains one or more other ingredients such as egg or egg products, flavoring, fruit juices, confectionery, stabilizer, color or water and the resulting mixture is frozen, while being stirred and is hardened by low temperature (Tressler and Evers, 1957).
2.2 History of ice cream:
The history of ice cream, in various forms, goes back at least as far the ancient Greeks and Romans, who cooled their wine with mountain snow and ice (Mariani, 1994). Marco Polo brought back from the orient a recipe for a frozen dessert based on milk and there is evidence that some forms of ice cream were brought by Catherine de
Medicis from Italy to France. Most of the ice cream during that period was made through a method of beating cream in a pewter pot that was shaken in a larger pot of salt and ice (Mariani, 1994).
The first improvement in the manufacture of ice cream was given to us by a New Jersey Woman, Nancy Johnson, who in 1846 invented the hand cranked freezer. This device is still familiar to many who make home made ice cream today (Davidson, 1999). Ice cream became a popular Luxury food, but almost all of it was made at home until 1851, in where, Jacob Fussel, a Baltimore milk dealer, established the first ice cream plant (Mariani, 1999). Ice cream became a national favorite during the early 1900 after Soda fountains introduced Sodas, Sundaes and other new ways of serving it (Mariani, 1999). During world war one ice cream was declared an “essential foodstuff” so that its ingredients were not rationed, and by 1919 Americans were eating 230 million gallons of ice cream per year and it became known as an “American typical food”, like hamburgers and hotdogs and in 1940 the figure was up to 318 million gallons (Mariani, 1999). About 1926 the first successful commercially continuous process freezer was perfected. Today multicylinder continuous freezers can turn out over 3800 liters of uniformly frozen ice cream per hour (Potter, 1978). The ice cream industry as we know it today has been mainly developed in the United States. The development of the ice cream industry can be most quickly told by listing the approximate dates of some important methods of processing and merchandising (Arbuckle, 1966). The term, “ice cream”, is found in an advertisement which appeared in the New York Gazette of May 19, 1777, by Philip lenzi, who termed himself a “confectioner from London”, which reads as follows: “May be had almost every day, ice cream; like wise, ice for refreshing wines, etc” (Eckles and Macy, 1951). 2.3 Nutritive value of ice cream:
The nutritive value of ice cream varies with its composition; however, all the constituents of milk are present in a concentrated form (Eckles and Macy, 1951). To ice cream may be added such materials as eggs, gelatin, fruits, nuts, chocolate, and bakery products, all of which add to its nutritive value (Eckies and Macy, 1951).
The milk products which go into the mix contain the same constituents as does whole milk, but in different amounts. Milk and its products, such as ice cream, are among the richest sources of calcium, phosphorus, and other minerals of vital importance in building good bones and teeth (Arbuckle, 1966). Small amounts of iron, copper, zinc, aluminum, cobalt, iodine, traces of silicon and boron are present in milk. The distribution of calcium in foods other than milk and dairy products is not extensive (Eckies et al., 1982).
2.4 Ice cream ingredients:
The fact that ice cream comes in many flavors and types leads a person to believe that ice cream is a complex and confusing product
(Varnam and Sutherland, 1994). All ice cream has a general formula, which can be added to or slightly modified to create the desired product. The major constituents (ingredients) in the ice cream formula backbone are milk fat, milk solids not fat, sweetener, stabilizer and/or emulsifiers, water and air (Varnam and Sutherland, 1994). Fig. (2.1): Soft serve ice cream is the perfect frozen dessert after any meal. 2.4.1 Milk fat:
Milk fat, the most important constituent of ice cream, is high in food value and high in cost (Arbuckle, 1966). Silliker et al. (1980) found that milk fat is provided primarily by fresh cream, butter oil, sweet butter and to a lesser extent, whole milk and other dairy products. The fat of ice cream varies from 8% to more than 20% in special products (Petersen, 1950). Milk fat is an important constituent influencing the texture of ice cream by mechanically obstructing ice crystal growth (Marshall and Arbuckle, 1996). Keeney (1958) has reported that a certain amount of fat destabilization is necessary to obtain good texture properties. Solid fat content, which measures the percentage of solid fat at a specific temperature, is usually used to evaluate dairy products (Kaylegian and Lindsay, 1995). Experiments from Berger and White (1971) and Berger et al. (1972) proved that fat destabilization has a significant influence on parameters such as dry appearance, creamy mouth feel and melt-down behavior of ice cream.
When milk fat was modified to contain more unsaturated fat, the softer milk fat influenced properties such as melting point and processes such as churning (Ashes et al., 1997).
1. Milk fat contributes richness and body, promotes a smooth textured ice cream, contributes a characteristic flavor, and serves as a carrier of other flavor components (Medved, 1978). The number of double bonds in fatty acids influences melting behavior and oxidative stability (off flavors), whereas distribution of the fatty acids in the triglyceride structure influences crystallization behavior, melting behavior and nutritional aspects (Hawke and Taylor, 1995; Kaylegian and Lindsay, 1995). Several studies indicated that a high content of unsaturated fatty acids in milk fat increases the risk of oxidation and production of off flavors (Lin et al., 1996a; Ashes et al., 1997; Focant et al., 1998; Im and Marshall, 1998). The higher the number of double bonds in a fatty acid chain, the lower the melting point (Walstra, 1995). Although the impact of fat concentration on the appearance and texture of foods is well known, its influence on flavor release and perception is still not well understood (Moore, 1991; Lucca and Tepper, 1994). 2.4.2 Milk solids non fat: Milk solids non fat are high in food value and inexpensive, but they add very little to flavor except indirectly by improving the body and texture (Arbuckle, 1966). Bennion (1975) reported that commercial ice cream may be reinforced with milk solids by the use of evaporated skim milk or non fat dry milk. He also added that too high percentage of evaporated milk gives a condensed milk flavor and a sandy ice cream, the latter resulting from the crystallization of lactose at the low temperature of the holding room. The most common sources for milk solids non fat used in frozen desserts are fresh skim milk, condensed skim milk, not fat dry milk powder, and condensed whey or whey powder (Desrosier, 1977). Higher levels of milk solids non fat permit higher overruns without textural breakdown (Potter, 1978). Water binding is a property of whey protein concentrate that can be utilized in frozen desserts to delay development of coarseness (Morr, 1989). The water binding capacity of whey protein concentrate (WPC) is influenced by protein concentration, mineral content and the extent of heating during manufacture (Sienkiewicz and Riedel, 1990). Protein interacts at the oil water interface during homogenization to stabilize the fat emulsion and during freezing, proteins function to control destabilization of fat (Goff et al., 1989; Mangino, 1992; Goff, 1997). Increased amount of whey protein at the oil water interface lowers surface tension and slightly increases mix viscosity that produces a drier ice cream and enhances partial coalescence in the freezer (Goff et al., 1989). 2.4.3 Sugar and sweetening agents:
The chief characteristic taste of ice cream is sweet. The major sugar used is sucrose (cane or beet sugar), because of its solubility and its high sweetening power, but other sugars, notably glucose syrups produced from corn flour by hydrolysis of the starch, are used
(Robinson, 1981).
Arbuckle (1986) and Berger (1976) indicated that functional characteristics that corn syrups impart on ice cream have long been recognized by the industry. They have been reported to contribute a firmer and more chewy body to the ice cream along with improving the shelf life of the finished product. Sweetening agents usually are not highly contaminated, but the degree of contamination is dependent upon the methods of production and upon storage (Foster et al., 1958). Olson (1966) mentioned that significant differences existed in melt down properties among ice cream made with corn sweeteners of different dextrose equivalent values. Eopechino and Leeder (1967) observed that ice cream with 25 -65% of sucrose replaced by corn sweeteners of high maltose content had a slower melting rate than the product with no corn sweetener added. Sweeteners play a major role in the sensory acceptance of many foods, especially beverages. Different sweetener types may provide similar sweetness but simultaneously impart different “flavor” characteristics to the beverage system in which they are used (Moskowitz, 1972; Baldwin and Korschegen, 1979; Redlinger and Setser, 1987). 2.4.4 Stabilizing agents: Stabilizers are used to prevent the formation of objectionable large ice crystals in ice cream and are used in such small amounts as to have a negligible influence on food value and flavor (Arbuckle, 1966). Peckham (1974) mentioned that commercially made ice cream may have from 0.3- 0.5% of a stabilizer such as gelatin or gum Arabic to keep the materials in dispersion. The first substance used was gelatin, which, on hydration, produces a gel network during a period of about four a hours at 5°C (aging). Other stabilizing agents do not require anytime for hydration (Robison, 1981). Many other substances are used now for the stabilization of ice cream. These include sodium alginate, locust been and guar gums, sodium carboxy methyl cellulose (CMC), carrageen and other seaweed derivatives (Robison, 1981). Flack (1981) indicated that a wide variety of stabilizers are being used in the ice cream industry, singly or in combination. The function of stabilizers in ice cream is attributed to their water binding capacity by forming a three dimensional network of hydrated molecules throughout the system. In this way they retard ice crystal formation, growth, improve mix viscosity, air incorporation, body texture and melting properties (Nielsen, 1984).
2.4.5 Emulsifying agents:
An emulsifier is a substance which produces an emulsion of two liquids that do not naturally mix. There are two types of emulsifiers used in the manufacture of ice cream (Parikh, 1977).
These are the mono and diglycerides derived by chemical reaction from naturally occurring glycerides, and polyoxyethylene derivatives of hexahydri alcohols, glycol, and glycol esters (Parikh, 1977).
The first emulsifying agent used was egg yolk (the active ingredient being lecithin) and this was followed by glyceryl mon stearate (GMS), egg yolk is a good natural emulsifier due to its content of lecithin (Potter, 1978). An emulsifying agent is really a surface active agent, which acts by reducing the energy required to maintain the integrity of the fat globules. It will also materially assist in obtaining larger numbers of smaller, more uniform air cells, which in turn, help to produce a smooth ice cream (Robinson, 1981). Several investigations have shown that the addition of emulsifiers leads to a significantly increased fat destabilization (Graf and Muller, 1965; Lin and Leeder, 1974; Goff et al., 1987; Goff et al., 1989; Berger, 1990 and Goff, 1997). The effect of the emulsifiers can be improved by an aging step, as the resulting fat crystallization and protein desorption additionally weaken the fat globule membranes (Kielmeyer and Schuster, 1986; Berger, 1990; Marshall and Arbuckle, 1996) 2.4.6 Flavoring materials: Flavor is a sensation which is derived from odor (Desrosier, 1977). He also added that ice cream owes its variety and popular appeal to many pleasing flavoring materials which can be used in its manufacture. The flavors are added directly into the mix when powders liquids or purees are used (Desrosier, 1977). Flavorings are added to ice cream in the form of extract, fruit, nuts, spices, chocolate, or coffee and only in amounts that will impart a mild, pleasant flavor (Peckham, 1974). Thanh et al. (1992) reported that interactions among volatile aroma substances and nonvolatile compounds depend on the physicochemical properties of the compounds and on the binding that may occur among them. Moreover butter fat is one of the chief factors affecting the flavor of ice cream (Bennion, 1975). Flavor perception is determined by the nature and quantity of the flavor compound and its availability to the sensory system as a function of time (McNulty and Karel, 1973; McNulty, 1987; Linssen et al., 1993). Pyenson and Tracy (1948) showed that some of the non dairy ingredients may contain considerable quantities of metals that could be significant in the development of off flavors in ice cream. Most ice cream is flavored by the addition of natural or synthetic flavor. Avery large amount of vanilla (either bean, vanillin or a mixture of these) is made and the second most popular flavors appear to be strawberry or raspberry, with chocolate coming third (Robinson, 1981). Wightwich (1970) concluded that flavors are used for different reasons: To provide a flavor when there is little or no initial flavor as in carbonated beverages, to mask an existing unpleasant flavor e.g. medicines, to boost a flavor which is too weak e.g. ice cream and to give a twist to a naturally occurring flavor. 2.4.7 Coloring materials: Ice cream have a delicate, attractive color which suggest or is readily associated with the flavor. Almost all flavors of ice cream should be slightly Colored (Arbukle, 1966). Only colors certified by the Food and Drug Administration should be used. Most ice cream makers purchase the desired colors in liquid or paste form (Arbukle, 1966). Foods may acquire their color from any of several sources (Potter, 1978). One major source is the natural plant and animal pigment. A second source of color comes from the action of heat on sugars. Thirdly, dark colors result from certain chemical interactions between sugars and protein referred to as the browning reaction or the Maillard reaction (Potter, 1978). There also are the complex color changes when a wide variety of organic chemicals present in foods come in contact with air (Potter, 1978). Noakes et al. (1996) observed slightly color differences in dairy products (milk, butter, cheese and ice cream) with a higher unsaturated fatty acid content. 2.4.8 Air: The amount of air dispersed in the ice cream influences quality and affects profits (Clark, 2000). More air lowers the total cost of ingredients, increasing profits. Too much air can decrease the quality. Air affects the smoothness, texture, price and weight (Clark, 2000). Legally no more than 50% of the ice cream can be air and the ice cream weigh more than 4.5 pounds per gallon (Clark, 2000). 2.5 Factors affecting of manufacturing procedures: 2.5.1 Mixing of ingredients: The term “ice cream mix” means a mixture or combination of ingredients used in the finished ice cream. A wide range of choice of ingredients for ice cream is now available from various sources (Tressler and Evers, 1957).These ingredients may by grouped as dairy products and nondairy products. It may or may not include flavoring and artificial coloring but it dose not include fruit or other non soluble ingredients (Tressler and Evers, 1957). Air and water in frozen desserts are necessary ingredients (Desrosier, 1977). The air, incorporated as very tiny air cells and the water, partly frozen into small ice crystals, give the product the palatability, the texture and body necessary for good quality and pleasant eating characteristics (Desrosier, 1977). Goff (1997) found that properly controlling the physical properties of an ice cream mix by further processing can favorably alter the texture and physical appearance of ice cream. The manufacture of ice cream is a relatively complex operation, with a series of steps which, in both compositional and microbiological terms, contribute to the overall quality of the ice cream (Robinson, 1981). 2.5.2 Heat treatment:
After the severe outbreak of typhoid in Aberystwyth in 1947 caused by ice cream made by a carrier of the disease, heat treatment regulations were introduced (Robinson, 1981). The primary purpose of pasteurization is to destroy all pathogenic microorganisms that might be present in the mix (Foster et al., 1958). Heating results in a reduction of the total numbers of bacteria, thorough mixing of the ingredients, dispersion of stabilizers and in physicochemical effects on the milk solids that are related to whipping ability and to body texture of ice cream (Foster et al., 1958).
Harvey and Hill (1952) reported that pasteurization of the mix is extremely important and should receive the greatest care and attention. They added that when milk is used, the bacterial content may be high, while the absence of any attempt to pasteurize the mix will facilitate the development of the original organism present later.
Ice cream mixture most not be kept for more than one a hour at any temperature which exceeds 7.2°C (45°F), before being pasteurized or sterilized (Robinson, 1981). Sterilization temperature not less than 148.8°C (300°F) for at least 2 seconds. In the care of HTST pasteurization or sterilization, full thermostatic control is required and a positive drive pump must be used to ensure the correct holding time. After such heat treatment and a careful storage of the liquid mix, it is to be excepted that the mixture should have a very low bacterial content (Robinson, 1981). The required time and temperature of pasteurization varies in different localities depending on state and city laws and ordinances (Tressler and Evers, 1957). Pasteurization is either the low temperature holding procedure (LTH) at 68.3°C for 30 minutes, the high temperature short time method (HTST) at 79.5C°for 25 seconds or the ultra high temperature method (UHT) at 138°C or higher (Silliker et al., 1980). Home made ice cream is made from pasteurized products. The mixture does not required pasteurization, although heating in double boiler for 15-20 minutes at a temperature of 63°C (145°F) blends ingredients thoroughly and may be an extra precaution from a health stand point (Bennion, 1975). Heat treatment may also change milk constituent (Alfa Laval Dairy Handbook). Some of the changes in membrane on heating whole milk occurred due to the heat treatment alone, independent of the interaction with skim milk protein (Houlihan et al., 1991). 2.5.3 Homogenization: The object of the homogenization is to reduce the fat globule size, so that globules do not rise to the surface (Robinson, 1981). Leviton and Pallansch (1959) found that homogenizing under the same conditions repeatedly, further decreases the fat globule size, narrowing the size distribution. Homogenization not only reduces the size of the fat particles so that churning will be avoided in the freezing process, but also adds to the viscosity of the mix (Petersen, 1950). Berger (1997) observed that homogenization of fat is employed to provide a stable emulsion and is considered an essential procedure during ice cream milk processing. All commercial ice cream milk is homogenized providing a smoother texture, better body and improved whipping quality. Homogenization is usually done at the same temperature at which the product is pasteurized (Tressler and Evers, 1957). Bennion (1975) mentioned that homogenization increases the viscosity of the mix, which favors a better retention of air. Ice cream made from a homogenized mix appears slightly rich in fat and is much smoother and more velvety than if non homogenized mix (Eckles and Macy, 1951). Parikh (1977) demonstrated that the mix is usually homogenized at a temperature from 145° F to 170° F because at a low temperature (120-130° F) homogenization increases the formation of clumps of fat globules, increases the viscosity and increases the freezing time in batch system. Moreover he reported that the mix may be cooled to 150° F for homogenization a desirable practice to reduce the intensity of the cooked flavor and length of time. The mix has to be held at high temperature especially when homogenization is not completed in 30 minutes (Parikh, 1977). The pressure used for homogenization depends upon several factors: desired viscosity, composition of the mix, stability of the mix, temperature used and construction of the homogenizing machine. He also added that a pressure of 2000-2500 Ib/inch² with single stage homogenizer or 250-300 lb/inch² on the first stage and 500 lb/inch² on the second stage homogenizers will usually give good results for an average mix. In a more recent study, Thomsen and Holstbory (1998) found that homogenization pressure only has a minor effect on the final product. Repeated homogenization has shown benefits in other dairy products, such as sour cream where “dual homogenization” is recommended if a heavy body product is desired (Kosikowski and Mistry, 1997). It is generally recognized that efficient homogenization of ice cream mix is of particular importance to the quality of the finished product and that even small variations from the optimum conditions of treatment can lead to significant deterioration of consistency and texture (Stistrup and Andreasen, 1966). 2.5.4 Cooling: Cooling the mix immediately after homogenization to 32-40°F is essential, after which it should be held in aging tanks until used (Parikh, 1977). Unless the mix is cooled to a temperature of 40°F or lower, it will become very viscous and the ice cream will not meltdown smoothly (Parikh, 1977). Robinson (1981) mentioned that it must be cooled to not more than 7.2°C (45°F) within 1½ hours of being heated and must be kept at such temperature until it is frozen. The temperature should be reduced rapidly to between 34-40°F to prevent bacterial multiplication (Harvey and Hill, 1952). Zamorani and Spettoli (1988) reported that recourse of refrigeration is to easiest practice to ensure proper storage, genuineness and hygiene of food. However, the delivering cycle can be affected by interruption in refrigeration (Maggi, 1994). 2.5.5 Aging: The mix is then aged for at least four hours and usually overnight. The overnight aging usually gives the best results (Goff, 1998). Also he added that the protein and the emulsifiers interact and cause the reduction in stabilization of the fat globules. This process improves the whipping quality of the mix, improves the body and the texture of the ice cream. The aging process is performed in insulated and refrigerated storage tanks (Stogo, 1998). The mix temperature is then maintained at as low temperature (5°C) as possible without freezing (Stogo, 1998). There is little change in total count unless additional contaminants are introduced from the vats used for aging. Moreover 16-24 hours at 4.4°C (40°F) has a little effect on the total bacterial count of ice cream mix (Foster et al., 1958). 2.5.6 Freezing: Freezing of ice cream mixture is accomplished by circulating cold brine or by allowing ammonia to expand directly around the walls of the cylinder surrounding the mix (Eckles and Macy, 1951). There are two general types of ice cream coolers, namely the “batch” and the “continuous” freezers. The batch freezer is the more commonly used, while the continuous type is adaptable for use in factories producing relatively large volumes of ice cream (Eckles and Macy, 1951). Desrosier (1977) concluded from his studies that the amount of water frozen as ice in the freezer varies between 30% and 60%, depending on drawing temperature and composition of the mix. Freezing must be quick to prevent the growth of large ice crystals that would coarsen texture and air cells must be small and evenly distributed to give as table frozen foam (Potter, 1978). The outer container of an ice cream freezer is usually made of a poor conductor of heat, such as wood. The container that holds the ice cream mixture inside the wooden outer container is made of metal, which permits the rapid absorption of heat from the ice cream mixture (Bennion, 1975). 2.5.7 Overrun: The increase is product volume resulting from air incorporation is referred to as overrun and is defined as the volume of mix (Desrosier, 1977). Varnam and Sutherland (1994) showed that “the percentage overrun” is the calculated as follows: {(volume of ice cream – volume of mix)/ volume of the mix} × 100. The range overrun in ice cream is usually from 70-100% (Potter, 1978). Home made ice cream usually have no more than 30-40% overrun, whereas commercial ice cream have at least 80% overrun and sometimes 90-100%. The higher percentage of overrun in commercial ice cream in comparison to home made products results from a better control of freezing conditions, such as the rate of freezing and the stage of hardness at which the freezing is discontinued (Bennion, 1975). Sakurai et al. (1996) found that ice cream with low overrun melted quickly, whereas ice cream with high overrun began to melt slowly and had a good melting resistance. This slower melting rate in the ice cream with high overrun was attributed to a reduced rate of heat transfer due to a larger volume of air but may also be due to the more tortuous path through which the melting fluid must flow (Hartel et al., 2003). 2.5.8 Hardness: An inverse relationship between hardness and overrun has been noted by many researchers (Tanaka et al., 1972; Goff et al., 1995; Wilbey et al., 1998). Both the ice crystal size and ice phase volume contribute to the hardness of ice cream. Wilbery et al. (1998) noted that the hardness of ice cream was exponentially related to the ice phase volume. Some of the more important factors affecting the hardening time are size and shape of package, air circulation, temperature of the air, section of the room, temperature of ice cream drawn from the freezer, composition of the mix and percent overrun (Arbuckle, 1966). 2.5.9 Packaging: A food package is a structure designed to contain the food product in order to make it easier and safer to transport, to protect the product against contamination, damage or degradation, to provide a convenient means for dispersing the product and to protect the contents against deterioration during storage, transportation and distribution (Stanely et al., 1970). Packaging of food is hence provided at the point of production, processing or at distribution centers (Anandaswamy et al., 1980). Packaging forms the last link in chain of production, processing or at distribution, it still plays an important in role delivering the contents “Safe” to the ultimate user. Besides, attractive functional package performs the job of a good sale man giving an image to the product (Anandaswamy et al., 1980). Although modern packaging adds cost factors to the food, it protects food against penetration of microorganisms, rodents, man and nature and it develops greater appeal for the food and permits basic label and manufactures information. It also saves on waste and moisture loss and permits shipment for long distances to market (Kosikowski, 1982). The influence of packaging on contamination of food may be direct, due to the presence of microorganisms in air and water vapor (Lubieniecki, 1972). Packaging is said to increase the product price, but in fact decreases distribution cost, improves keeping quality and overall hygienic quality of the packaged product (Bojkow, 1986). The ice cream will normally be packaged, either in bulk, in smaller sized ‛family packs of one liter or less, or in individual’ retail packs (Robinson, 1981). Some ice cream is sold directly from a dispensing freezer as ‛Soft serve’ ice cream, either on cones or in various types made up sweets in cafes and restaurants or from vehicles complete with their own electricity generation equipment (Robinson, 1981). The volume of ice cream packaged in the various carton sizes depends upon the type of market outlet and local consumer buying practices (Anandaswamy et al., 1980). Packaging protects food during storage, transportation and distribution against deterioration, which may be physical or biological (Anandaswamy et al., 1980). 2.5.10 Storage and distribution: The ice cream must stay frozen solid for quality assurance. When the ice cream leaves the factory, it must be stored at a constant, uninterrupted, freezing cycle at low temperatures to avoid problems (Goff, 1998). Problems at retail level can arise from overfilling of the display cabinet, heat from the display lamps or hot air from incorrectly positioned circulation fans or displaying ice cream together with the semi frozen goods (Goff, 1998). Eckies and Macy (1951) mentioned that refrigerated, insulated trucks are commonly used to transport ice cream from the manufacture to the retail distributor. The shelf life of any food commodity should combine the two considerations of safety and organoleptic property of the product. Moreover they reported that it is more economical to ship the products of which ice cream is made to a point from which the finished ice cream can be easily distributed. 2.6 Defects of ice cream: 2.6.1 Body and texture defects: Body and texture defects include coarse icy texture, which is due to the presence of ice crystals of such a size that is noticeable when the ice cream is eaten (Flores and Goff, 1999b). The term body, used in relation to ice cream, refers to the consistency or richness of the product (Peckham, 1974). Desrosier (1977) mentioned that body defects are commonly described as crumbly, soggy and weak, while the common texture defects are coarse, icy fluffy, sandy and buttery. He also reported that a crumbly body or a flaky, snowy characteristic in ice cream is caused by low stabilizer or emulsifier, low total solids or coarse air cells.
Batch pasteurization Homogenization Cooling
Blending
Continuous pasteurization / Homogenization /Cooling
Continuous freezing
Packaging Aging
Batch freezing / whipping
Addition of bulk ingredients Addition of flavor and color
Hardening Storage and distribution
Fig. (2-2): Ice cream processing adapted from the University of Guelph (Goff, 1998).
. Marshall and Arbuckle (1996) demonstrated that a coarse texture is the most frequently cited defect in ice cream. As this defect becomes pronounced, a gritty or icy mouth is followed by a relatively cold sensation in the mouth caused by excessively large ice crystals. To achieve small initial ice crystals, the ice cream mix must be rapidly sub cooled to the point of the maximal nucleation rate (Hartel, 1996). A fluffy texture is a spongy characteristic that is caused by incorporation of large amounts of air as large air cells, low total solids or low stabilizer content (Goff, 1998). A gummy body defect is opposite of crumbly in that it imparts a pasty or putty like body (Goff, 1998). Ice cream texture is dependent upon the number, size, shape and arrangement of ice crystals and other particles (Arbuckle, 1966). A sandy texture is due entirely to fairly large lactose crystals which are slow to dissolve. This defect may be controlled by reducing the milk solids not fat content of the mix, acid standardization, replacing part of the cane sugar content with the dextrose and maintaining uniformly low storage temperature (Arbuckle, 1966). 2.6.2 Flavor defects: Flavor defects can be classified in five different ways. This includes the flavoring system, which is that it lacks flavor or the flavor is too high or that the flavor is the unnatural (Goff, 1998). The dairy ingredient flavor defects include acid, salty, old ingredient, oxidized/metallic, rancid or whey flavor (Smith et al., 1999). The most commonly used system in flavor assessment for ice cream is the dairy ingredient flavor defect system (Flores and Goff, 1999b). Abd El – Rahman et al. (1997) claimed off flavors in butterfat can be carried to second products, such as ice cream and affect consumer acceptance. However, milk fat with a high mono unsaturated fatty acid content compared with a high polyunsaturated fatty acid content did not exhibit oxidation problems (Lin et al., 1996a, 1996b). 2.6.3 Shrinkage defects: A very troublesome defect in ice cream is shrinkage because there appears to be no sigle cause or remedy (Goff, 1998). This defect shows up in hardened ice cream and manifests itself in reduced volumes of ice cream, usually by pulling a way from the top and/or sides of the container (Flores and Goff, 1999a). They also added that structurally, it is caused by a loss of spherical air bubbles and formation of continuous air channels. Goff (1998) indicated that some factors believed to be associated with the defect include that Some emulsifier seem to enhance shrinkage, freezing and hardening, both low and high storage temperatures appear to contribute, ultra smooth ice cream as can be produced in continuous freezer, type of container, partial destabilized protein, season of the year as more shrinkage occurs in winter months and methods of handling in grocery store cabinets. 2.6.4 Color defects: Ice cream should possess a pleasing color, if its color is too high or if it lacks color, it is objectionable (Eckles and Macy, 1951). The ideal color is the considered of the flavor, true in shade and neither too pale nor too intense (Arbuckle, 1966). Uniform, natural color is desirable ice cream. An uneven color results if the color is not properly added and also it care is not exercised when changing flavor. Excessive color is the result of adding too much artificial color to the mix. An unnatural color describes defects due to insufficient (pale) color, excess (intense) color and colors that are not characteristics (true in shade) of the flavor (Arbuckle, 1966). 2.7 Microbiology of ice cream ingredients: A commercial prepared ice cream must be made under sanitary conditions, as the bacteria can grow easily in milk mixtures (Foster et al., 1958). Many cities and states have no bacterial standards for raw or pasteurized cream. Some ice cream is still made from cream with high total bacterial counts and such cream may be the chief dairy product source of the bacteria in ice cream (Foster et al., 1958). Skim milk powder may, on occasions, contain numbers of Bacillus cereus and although this is not often a health hazard, it is preferable for the numbers to be kept as low as possible (Robinson, 1981). Sugar syrup, whether sucrose or mixtures of sucrose and corn syrups again should contain only a few yeasts, but it should be remembered that osmophilic yeasts may be able to grow in these syrups (Robinson, 1981). Stabilizers and emulsifiers rarely present problems, but gelatin as an animal product, may be a hazard and should be obtained from reputable supplies and kept quite cool and dry, as indeed should all the dry materials which are used in ice cream manufacture (Robinson, 1981). The numbers of bacteria which are present in ice cream will defend very largely upon the numbers and types in the raw materials, especially milk, cream, condensed or dried milk (Eckles and Macy, 1951). Ice cream should be made from high grade raw materials and be handled as carefully as any dairy product, even though low temperatures protect it against deterioration in storage (Eckles and Macy, 1951). The various Gram negative and Gram positive psychrotrophic species are listed and with respect to pathogenic psychrotrophs, emphasis is given on Listeria monocytogenes, Yersinia enterocolitica and Bacillus cereus. The influence of psychrotropic bacteria on the quality of raw milk, pasteurized milk, UHT milk, butter, ice cream, cheese and milk powders is examined (Champagne et al., 1994).
Methods that can be used to eliminate or control the development of psychrotropic bacteria include low or high temperature, chemicals, gases, the lactoperoxidase system, lactic acid bacteria, micro filtration, bactofugation, lactoferrin related protein, sanitation, flavors and naturally occurring spore germinants (Champagne et al., 1994)
2.8 Potential microbiological hazards associated with ice cream:
Vasavada (1988) Padhy and Doyle (1992) demonstrated that many bacterial agents are capable of causing diseases or intoxication in a susceptible host through consumption of raw milk or milk products. Ice cream, a milk based products are good media for microbial growth due to high nutritive value, almost neutral pH value
(pH 6-7) and long storage duration of ice cream. However, pasteurization, Freezing and hardening steps in the production can eliminate most of the microbiological hazards (Bell and Kyriakides,
1998). Pasteurization is the most commonly applied heat treatment in the dairy industry (Andreasen and Nielsen, 1998). This can destroy almost all pathogenic bacteria in milk. The subsequent process that subjects the mixtures to freezing temperature can also inhibit the growth of any remaining flora. Hardening is also on important control point that further reduces the hazards (Andreasen and Nielsen, 1998).
Furthermore they reported that as automatic machines are commonly used for ice cream making in dairy industry, the chance of contamination through direct hand manipulation can be reduced.
Nevertheless, there are some steps in the production of ice cream that can lead to the microbiological hazards (ICMSF, 1998).
Heat treatment by pasteurization can destroy most of the specific pathogens that pose risk to public health. However, the potential microbiological hazards found in the final products can still be introduced after pasteurization through adding contaminated ingredients and improper handling procedures (Marshall, 1998). This is especially important in the preparation of soft ice cream as its final stage of production is carried out at point of sale; some pathogens that can survive in food even at low temperature include Salmonella spp.,
Listeria monocytogenes, Campylobacter spp. and Yersinia spp.
(ICMSF, 1996). In order to produce ice cream which will not only be a pleasant and nutritious food, but also one which does not present a health hazard, it is necessary to pay attention to a wide range of details
(Robinson, 1981). These include careful selection and testing of the raw materials, the use of correct processing conditions in equipment properly cleaned and adequately sanitized and finally satisfactory handling of the product at the sales point. Only a small quantity of ice cream has to be contaminated to produce a hazard for a large number of people and to a void this, it is essential that all operators are properly trained in every way, that bacteriological control should be carried out carefully and the results acted upon (Robinson, 1981).
2.9 Major diseases transmitted through ice cream: The same dangers of illness caused by drinking raw milk are inherent in ice cream either made from raw milk and cream or handled under unsanitary conditions (Silliker et al., 1980). With few exceptions, outbreaks occurred in recent years have been caused by ice cream made not in commercial establishments but rather at homes where a combination of faulty practices occurred such as use of raw milk, cream and eggs, inadequate heat treatment and contamination
(Silliker et al., 1980).
Table (2-1): Hazards and typical control in the production of ice
cream:
Process Hazard Control measure Raw materials Presence of pathogens • Purchase materials from reputable suppliers • Intake testing Pasteurization Survival of the pathogens • Corrected time/ temp. control • Maintenance of equipment • Effective disinfection programme of equipment Aging Recontamination • Hygienic design/ cleaning/ disinfection Growth of microorganisms of equipment and utensils • Temp.: <5°C Filling in packaging step Recontamination • Hygiene design/ environmental hygiene of equipment of utensils Addition of ready to eat Recontamination • Purchase materials from reputable ingredients (e.g.: fruits, nuts suppliers or syrup) • Environmental hygiene of storage area, equipment and utensils • Hygiene of addition practice Hardening Recontamination • Cleaning and disinfection of equipment and utensils Storage and transportation Growth of microorganism • Tem. < - 18°C • Discard the defrosted products
Source: ICMSF. Microorganisms in foods. 6 Microbial ecology of
food commodities. P. 563.
Ice cream has been incriminated as a transmitter of pathogenic bacteria, but out breaks of disease due to commercially manufactured ice cream are rare (Foster et al., 1958). At various times ice cream has been found to harbor typhoid fever, paratyphoid fever, diphtheria and scarlet fever organisms (Foster et al., 1958). Many major food poisoning outbreaks have been caused by human contamination. One, in 1945, was due to staphylococci carried by a worker in the cook house of an army hospital, which were introduced into batches of ice cream mix after the ingredients had been cooked (Robinson, 1981). Moreover around 700 people were affected by a staphylococcal toxin which developed during that period. There are still cases of food poisoning caused by ice cream reported from overseas, although most countries, in which there is any appreciable production and sale of ice cream, have relatively strict standards and heat treatment requirements (Robinson, 1981). Gastroenteritis caused by Salmonella in ice cream is characterized by abdominal cramps and diarrhea, Vomiting, fever and headache. Antimicrobial therapy is not indicated in uncomplicated gastroenteritis, which typically resolves with in one week (Noakes et al., 1996).
Fig. (2-3): Large ice ream plant for production of 5000-10000 1/h of various types of ice cream
A. Raw material storage. 11. Cartoning unit. B. Dissolving of ingredients and mixing. 12. Cup/cone filler. 1. Mixing unit. 13. Hardening tunnel. 2. Plate heat exchanger. 14. Cartoning line. 3. Mixing tanks (at least two for continuous 15. Return covering or for empty processing). trays. C. Pasteurization, homogenization and fat 16. Tray tunnel extruder. standardization of the mix. 17. Chocolate enrobing unit. 4. Plate heat exchanger. 18. Cooling tunnel. 5. Homogenizer. 19. Wrapping unit. 6. Tank of AMF of vegetable fat. 20. Cartoning unit. D. Ice cream production plant. 21. Cold storage. 7. Ageing tanks. 8. Continuous freezer. 9. Bar freezer. 10. Wrapping and stacking unit. CHAPTER THREE
MATERIALS AND METHODS
3.1 Ice cream sample collection:
The present study was undertaken in the period from September
2003 to March 2004 in the three cities of Khartoum State (Khartoum,
Khartoum North and Omdurman).
A total of 100 samples were evaluated, 60 samples were collected from each of Khartoum, Khartoum North and Omdurman.
The other 40 samples were manufactured by Looli factory. The percentage of the ingredients varied from locality to another according to price and a viability. The flavors added to the samples were chocolate, vanillia, coconut, strawberry and mango.
The samples were collected in ice boxes during transportation to the laboratory and then the samples were preserved in a refrigerator at 4 - 5°C.
3.2 Chemical analyses of ice cream:
The chemical tests were carried out in duplicate at the
Laboratory of Department of Dairy Production, Faculty of Animal
Production, University of Khartoum and they included the following way: 3.2.1 Determination of fat content:
Fat content was determined by Gerber method described by
Bradley et al. (1992).
Ten ml of sulfuric acid (density 1.815 gm/ ml at 20ºC) were poured into clean dry Gerber tubes, then 5 gm ice cream were added, followed by the addition of 1 ml amyl alcohol and 5 ml distilled water at 20ºC. The contents of the tube were thoroughly mixed till no white particles were seen. The tubes were then centrifuged at 1100 revolutions per minutes (rpm) for 5 minutes. The tubes were transferred to a water bath at 65ºC for 3 minutes, after which the fat content was immediately read.
3.2.2 Determination of protein content:
The protein content was determined by Kjeldahl method according to AOAC (1990).
In a Kjeldahl flask, l0 gm ice cream sample were placed followed by addition of Kjeldahl tablets (each tablet contained 1gm
Na2SO4 and the equivalent of 0.1mg Hg). Twenty five milliliters of concentrated sulfuric acid (density 1.86gm/ ml at 20°C) were added to the flask and the mixture was then digested on a digestion heater until a clear solution was obtained (3 hours), the flasks were then removed and left to cool. The digested samples were poured in volumetric flasks (100 ml) and diluted to 100 with distilled water. Five milliliters were taken and neutralized using 10 ml of 40% NaOH. The distillate was received in a conical flask containing 25 ml of 2% boric acid and
3 drops of indicator (bromocresol green + methyl red). The distillation was continued until the volume in the flask was 75 ml. The flasks were then removed from the distillator and the distillates were titrated against 0.1N HCl until the end point was obtained (red colour).
Protein content was calculated as follows:
Nitrogen (%) = T × 0.1 × 20 × 0.014 × 100 Weight of sample
Protein (%) = Nitrogen (%) × 6.38
Where:
T: Titration figure.
0.1: Normality of HCl.
0.014: Atomic weight of nitrogen/ 1000.
20: Dilution factor.
3.2.3 Determination of total solids content:
Total solids content of ice cream sample were determined according to the modified method of AOAC (1990).
Two grams of ice cream sample were placed in a clean dried flat bottomed aluminum dish. The dishes were heated on a steam bath for 10-15 minutes and then the dishes were transferred to an air oven for
12 hours at 50°C. The dishes were placed into desiccator to cool and then weighed. Heating, cooling and weighting were repeated several times until the difference between two successive weightings was less than 0.5 mg. the total solids content was calculated as follows:
Total solids (%) = W1 × 100 W0 Where:
W1: Weight of sample after drying.
W0: Weight of sample before drying.
3.2.4 Determination of ash content:
The ash content was determined according to AOAC (1990).
Two grams of ice cream were weighted into a suitable clean dry crucible and evaporated to dryness on a steam bath. The crucibles were placed in a muffle furnace at 550°C for 1.5-2 hours, cooled in a desiccator and weighted. The ash content was calculated as follows:
Ash % = W1 × 100 W0 Where:
W1 = Weight of ash.
W0 = Weight of sample. 3.2.5 Determination of total sugars content: Total sugars were assessed according to Lane and Eynon micrometric method AOAC (1984). Ten grams of ice cream sample were transferred to a 250 ml volumetric flask. A 100 ml of distilled water were carefully added and then neutralized with 1.0N NaOH to a pH 7.5-8.0. About 2 ml of lead acetate were added and the flask was then shacked and left to stand for 10 minutes. Then 2 grams of sodium oxalate were added to remove the excess lead. Distilled water was again added to make the volume to mark (250 ml). The solution was then filtrated and 50 ml of its filtrated were pipetted into a 250 ml volumetric flask. To the new mixture, 50 g citric acid and 50 ml distilled water were slowly added. The contents of the flasks were boiled gently for 10 minutes to invert to sucrose and when cooled a few drops of phenolphthalein were added. In order to neutralize the mixture, a 20% NaOH solution was continuously added until color turned pink. Immediately 1.0N HCl was added until the color of the mixture disappeared and the volume was made to mark before titration. Standard method of titration: Ten ml of mixed solution of Fehling (A) and (B) were pipetted into a conical flask. A burette was filled with the clarified sugar solution and running the whole volume required to reduce the Fehling’s solution so that 0.5-1.0 ml was still required to complete the titration. The contents of the flasks were mixed and then heated to boiling for 2 minutes. Three drops of methylene blue indicator were added. Then the titration was completed until the color has completely disappeared. Calculation: Mg total sugar in 100 ml = Factor × 100 Titer
Total sugar (%) = mg/ 100g × dilution × 100 1000 × wt. taken Factor = mg of invert sugar corresponding to 10 ml of Fehling’s solution. (The factor is obtained from the table of invert sugar). 3.2.5.1 Determination of reducing sugars content: For most juices, the reducing sugars were very low, so that filtrate can be used directly for titration according to AOAC (1984) using the following equation for calculation: Reducing sugar (%) = mg/ 100g × dilution × 100 1000 × wt. taken
(The factor is obtained from the table of glucose). 3.3 Microbiological examination of ice cream: 3.3.1 Sterilization of equipment and media: Flasks, test tubes, pipettes and Petri dishes were sterilized by hot air oven at 160°C for 60 minutes. The media were prepared as prescribed by the manufacturer and brought to boiling before sterilization by autoclaving at 121°C for 15 minutes. The media were then allowed to cool at 45-46°C before pouring into Petri dishes (Singleton, 1992). 3.3.2 Microbiological media: 3.3.2.1 Standard plate count (SPC): Standard plate count agar was used. Ingredients Grams/ liter Casein enzymic 5 gm Hydrolyste 2.50 gm Yeast extract 1 gm Dextrose 1 gm Agar 15 gm Distilled water 1000 gm
pH 7±0.2.
3.3.2.2 Mac Conkey Agar: Mac Conkey Agar was used. Ingredients Grams/ liter Pancreatic digest of gelatin 17 gm Peptic digest of animal tissue 1.5 gm Casein enzymic hydrolysate 1.5 gm Lactose 10 gm Bile salts 1.5 gm Sodium chloride 5 gm Neutral red 0.03 gm Crystal violet 0.001 gm Agar 15 gm pH 7.1±0.2 3.3.2.3 Yeast extract agar:
Yeast extract agar was used 23 gm of yeast extract agar in 1000 ml and pH 7.2±0.2.
3.3.3 Plating, enumeration and counting of bacteria:
3.3.3.1 Preparation of sample dilution:
A representative sample of ice cream (1 gm) was diluted 1:10 with sterile distilled water, diluted serially (10-1-10-6) and one milliter from each the selected dilution after thorough mixing were carefully transferred into Petri dishes using sterile pipettes.
3.3.3.2 Enumeration of total bacteria:
The method described by Houghtby et al. (1992) was used.
From each dilution, 1 ml sample was aseptically transferred into sterile Petri dishes in duplicate, followed by adding 10-12 ml of standard plate count agar at 45-46°C. The Petri dishes were covered and mixed by gentle rotation then allowed to solidify. The plates were inverted and incubated at 37ºC for 48 hours.
The developed colonies were counted using colony counter, plates
25-250 or less than 25 colonies were selected. The average number of colonies in each dilution was multiplied by the reciprocal of the dilution factor and recorded as colony forming units/ gm. 3.3.3.3 Enumeration of coliform bacteria:
The method described by Christen et al. (1992) was used.
From each dilution, 1 ml sample was aseptically transferred into sterile Petri dishes followed by addition of 10-15 ml Mac Conkey
Agar medium at 44-46°C. The contents were allowed to solidify (5-10 minutes) on a leveled surface, then additional 3-4 ml Mac Conkey
Agar were added to each Petri dishes as on overlay to completely cover the surface of the solidified medium to inhibit surface colony formation. The plates were then inverted and incubated at 37°C for 48 hours.
The number of dark red colonies measuring ≥0.5 mm in diameter on
(15-150 cfu/ gm) plates were counted and resulted were recorded as follows:
Coliform count: Number of colony × factor of dilution = cfu/ ml.
3.3.3.4 Enumeration of psychrotrophic bacteria:
The method described by Frank et al. (1992) was used.
From each dilution, 1 ml sample was aseptically transferred into sterile Petri dishes, followed by adding 10-12 ml of standard plate count agar at 45-46°C, the Petri dishes were covered and mixed by gentle rotation and allowed to solidify. Then the plates were inverted and incubated at 7°±1°C for 10 days.
After determining the colony count the numbers were reported as psychrotrophic bacteria count per gm. 3.3.3.5 Enumeration of Yeast counts: The method described by Frank et al. (1992) was used. One milliliter from each dilution was carefully transferred into Petri dishes using sterile pipettes, then adding 10-12 ml of yeast extract agar into plates. It was mixed by gentle rotation and incubated at 25°C for 5 days. The developed colonies were counted using colony counter and plates counting 15-150 colonies in each dilution were multiplied by the reciprocal of the dilution factor and recorded as per gram or per milliliter. 3.4 Sensory evaluation: Ten untrained panelists were chosen to judge on the quality of ice cream in terms of color, flavor, texture, taste and overall acceptability, using a sensory evaluation sheet (Appendix 1). 3.5 Statistical analysis: Statistical analyse were performed using the Statistical Analysis System SPSS (10.5). General Linear Models (GLM) were used to determine the variation between machines and Looli factory ice cream flavored with chocolate, vanillia, coconut, strawberry and mango. Moreover, the variables were analyzed to test their effect on the chemical composition (fat, protein, total solid, ash and sucrose), microbial counts (total bacteria count, yeast, coliform and psychrotrophic bacteria) and sensory characteristics (color, texture, flavor, taste and overall acceptability) of ice cream. Means were separated using Duncan’s Multiple Range Test (P≤0.05).
CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 Flavors and chemical composition of ice cream:
Results in table (4-1) show the chemical composition of ice cream made by different producers.
The fat (P< 0.001), protein (P> 0.05), total solids (P< 0.01), ash
(P< 0.001) and sucrose (P> 0.05) were highest in Looli samples
(9.28±1.37, 2.69±1.03, 33.40±2.87, 0.64±0.19 and 9.14±1.17 respectively) compared to machines samples which have mean
(4.25±1.65, 2.49±0.87, 31.82±2.48, 0.39±0.21 and 8.98±1.34, respectively).
The present results were consistent with the finding of Roland et al. (1999) who reported that the fat content was the highest in control manufactured ice cream. Our results also were in agreement with the findings of Petersen (1950) who reported that the fat of ice cream varies from 8% to more than 20% in special product. This may be due to using low milk fat content with the machines samples.
Similarly Zheng et al. (1997) who reported that statistical analysis indicated that the addition of cream increased significantly the fat content of ice cream. This is important, as increases in fat content Table (4-1): Average chemical composition of ice cream samples from machines and looli factory:
Composition Machines Looli Sig. level
Fat (%) 4.25±1.65b 9.28±1.37 a ***
Protein (%) 2.49±0.87 a 2.69±1.03 a NS
Total solids (%) 31.82±2.48b 33.40±2.87 a **
Ash (%) 0.39±0.21b 0.64±0.19 a ***
Sucrose (%) 8.98±1.34 a 9.14±1.17 a NS
Means within the each row bearing similar superscripts are not significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
**: Highly significant: at (P< 0.01).
***: Very highly significant: at (P< 0.001).
have be shown to reduce ice crystal size (Keeney and Kroger, 1974) and affect sensory evaluation by causing a lubricating sensation in the mouth (Keeney, 1979; Arbuckle, 1986). The highest total solids content in ice cream made by Looli may be due to increase skim milk powder in milk based ice cream or added stabilizers and sugar in the mix. Ice cream mix with low total solids (high water content) has proportionately more water to freeze than a higher total solids mix
(low water content) hardened to the same storage temperature. The percent total solid of the ice cream mix is directly related to ice crystal size distribution (Flores and Goff, 1999a) and lower total solids ice cream contains lager ice crystals (Donhowe et al., 1991). Variations in solids content of just a few percent greatly influences ice crystal growth (Keeney, 1979).
Table (4-2) shows the chemical composition of ice cream made using different types of flavors. Although there was no significant (P>
0.05) difference between ice cream made using different type of flavors (chocolate, vanillia, coconut, strawberry and mango) in all chemical components expect total solids was significant (P<0.01) difference. Fat, protein and ash (P> 0.05) were highest in strawberry flavor ice cream (6.47±3.40, 2.81±1.07 and 0.53±0.27, respectively), while total solids (P< 0.01) was highest in ice cream made with chocolate flavor (33.88±3.89). The sucrose (P> 0.05) was highest in ice cream made with mango flavor (9.20±1.03). Table (4-2): Effect of type of flavor on chemical composition of ice
cream:
Composition Chocolate Vanillia Coconut Strawberry Mango Sig.level Fat (%) 6.32±3.31a 6.06±2.85a 6.09±2.60a 6.47±3.40a 6.39±3.01a NS Protein (%) 2.36±0.68a 2.76±1.13a 2.23±0.63a 2.81±1.07a 2.71±0.99a NS Total solids (%) 33.88±3.89a 31.62±2.23bc 32.25±1.93ab 31.75±2.47bc 32.77±2.38ab ** Ash (%) 0.50±0.21a 0.49±0.22a 0.48±0.23a 0.53±0.27a 0.47±0.25a NS Sucrose (%) 8.96±1.48a 9.15±1.20a 8.89±1.50a 9.04±1.17a 9.20±1.03a NS
Means within the each row bearing similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
**: Highly Significant: at (P< 0.01). Tables (4-3 and 4-4) show the chemical composition of different flavors. There was non significant (P> 0.05) difference between machines and Looli factory in chemical composition, while total solids was significant (P> 0.05) difference. In samples produced by machines mango, vanillia and chocolate ice cream showed highest values for fat, protein, ash and sucrose (4.70±2.26, 2.84±1.10, 0.45±0.25 and 9.21±1.40, respectively). However Looli ice cream revealed highest fat, protein, ash and sucrose for chocolate, mango, coconut and mango (9.94±1.45, 3.30±1.12, 0.71±0.16 and 9.64±0.68, respectively). A total solid (P< 0.05) was highest in machines ice cream with mango flavor (32.64±3.06) and Looli made with chocolate flavor (36.71±3.74). 4.2 The microbial count of ice cream: The result given in table (4-5) show the average total bacterial count, yeast count, coliform and psychrotrophic bacterial counts in ice cream made by different producers. The highest maximum average numbers of the standard plate count (P< 0.001) were obtained from ice cream made by machines (log 5.53±0.54), while the lowest minimum average were obtained in Looli ice cream (log 5.12±0.49). The maximum yeast, coliform and psychrotrophic bacterial counts were highest in Looli ice cream (log 6.24±0.54, 5.05±0.52 and 4.39±0.59, respectively) compared to machines ice cream which have an average log counts of 6.14±0.53, 4.99±0.42 and 4.21±0.48, respectively, although the difference was not significant (P>0.05).
Table (4-3): Chemical composition of flavored ice cream from
machines producers:
Machines Sig. Composition Chocolate Vanillia Coconut Strawberry Mango level
Fat (%) 3.90±1.29 a 4.07±1.58 a 4.26±1.40 a 4.33±1.74 a 4.70±2.26 a NS
Protein (%) 2.51±0.69 a 2.84±1.10 a 2.25±0.72 a 2.54±1.06 a 2.32±0.68 a NS
Total solids 31.98±2.74bc 31.52±1.77bc 31.78±2.17bc 31.17±2.63bc 32.64±3.06a * (%)
Ash (%) 0.43±0.19 a 0.45±0.25 a 0.33±0.11 a 0.44±0.29 a 0.32±0.13 a NS
Sucrose (%) 9.21±1.40 a 9.03±1.31 a 8.84±1.71 a 8.93±1.28 a 8.90±1.14 a NS
Means within the each row bearing similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
*: Significant: at (P< 0.05). Table (4-4): Chemical composition of flavored ice cream from Looli
factory:
Looli Sig. Composition Chocolate Vanillia Coconut Strawberry Mango level
Fat (%) 9.94±1.45 a 9.04±1.05 a 8.84±0.93 a 9.68±0.83 a 8.91±2.11 a NS
Protein (%) 2.13±0.63 a 2.63±1.23 a 2.20±0.53 a 3.21±1.02 a 3.30±1.12 a NS
Total solids 36.71±3.74a 31.73±2.92bc 32.96±1.31ab 32.61±2.06ab 32.95±0.77ab * (%)
Ash (%) 0.61±0.19 a 0.54±0.16 a 0.71±0.16 a 0.65±0.21 a 0.70±0.20 a NS
Sucrose (%) 8.58±1.62 a 9.34±1.08 a 8.96±1.23 a 9.19±1.04 a 9.64±0.68 a NS
Means within the each row bearing the similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
*: Significant: at (P< 0.05). Table (4-5): Microbial quality of ice cream samples from machines
and Looli factory:
Sig.
Microbial content Machines Looli level
Total bacterial counts ( log10 cfu/ 5.53±0.54 a 5.12±0.49 a *** gm)
a a Yeast count ( log10 cfu/ gm) 6.14±0.53 6.24±0.54 NS
a a Coliform ( log10 cfu/ gm) 4.99±0.42 5.05±0.52 NS
Psychrotrophic count ( log10 cfu/ 4.21±0.48 a 4.39±0.59 a NS gm)
Means within the each row bearing the similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
***: Very highly significant: at (P< 0.001). It was clear that the average total bacterial count of ice cream made in the machines had high count than the other samples made by Looli factory. This might be due to the methods, tools and selling techniques which lacked aspects of public hygiene. Our results are also in agreement with the findings of Rossi (1990) who reported that the ice cream might be contaminated due to improperly cleaned servers and debris falling into uncovered tubes at point of selling. Similarly our results were in agreement with the findings of Robinson (1981) who mentioned that ice cream produced on a small scale often has a poor bacteriological quality than the output of a large scale factory, for often these small factories have no system of quality control at all. Another reason for this high average bacterial numbers was that the containers were continuously opened and reclosed for purpose of selling and this will allow more contamination by dust and hands to occur. The highest maximum average numbers of the yeast, coliform and psychrotrophic bacterial count of ice cream made by Looli factory may be due to using milk and raw materials from different sources or the heat treatment were not efficiency to destroy any pathogenic microorganisms. Table (4-6) show the average total bacteria count, yeast, colifrom and psychrotrophic bacterial counts in ice cream made using different flavors (chocolate, vanillia, coconut, strawberry and mango). Chocolate and strawberry showed maximum total bacteria count (log 5.64±0.59) and psychrotrophic count (log 4.44±0.54) respectively, while vanillia (log 5.10±0.47) and mango (log 4.13±0.59) were minimum count respectively. However, the maximum numbers of coliform (log 5.24±0.49) and yeast count (log 6.45±0.53) were obtained from ice cream made with vanillia and chocolate flavors (P< 0.05), while the minimum average were obtained coconut (log 4.84±0.32), strawberry (log 4.84±0.40) and mango (log 6.00±0.62).
Table (4-6): Average microbial quality of flavored ice cream:
Sig. Microbial content Chocolate Vanillia Coconut Strawberry Mango level Total bacteria count ( 5.64±0.59a 5.10±0.47a 5.36±0.51a 5.34±0.58a 5.38±0.56a NS log10 cfu/ gm)
Yeast count ( log10 6.45±0.53a 6.01±0.42bc 6.33±0.53ab 6.12±0.44ab 6.00±0.62bc ** cfu/ gm) Coliform count ( 5.16±0.49ac 5.24±0.49a 4.84±0.32bc 4.84±0.40bc 5.00±0.48ab ** log10 cfu/ gm) Psychrotrophic count 4.21±0.52a 4.26±0.47a 4.38±0.53a 4.44±0.54a 4.13±0.59a NS ( log10 cfu/ gm)
Means within the each row bearing similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
**: Highly significant: at (P< 0.01). The present results were generally, in agreement with the findings of Eckles and Macy (1951) who found that the numbers of bacteria which are present in ice cream will depend very largely upon the numbers and types of raw materials, especially milk, cream and condensed or dried milk. Tables (4-7 and 4-8) show the microbial content of ice cream made by different producers and flavors. The maximum total bacterial counts (P< 0.05) was obtained from chocolate produced by machines (log 5.97±0.37) and coconut produced by Looli factory (log 5.33±0.46). The maximum average yeast, coliform and psychrotrophic bacterial counts were obtained in chocolate and coconut (log 6.50±0.051, 5.22±0.46 and 4.35±0.55, respectively) in ice cream produced by machines. However the maximum in average of these counts were reported in coconut, vanillia and strawberry (log 6.64±0.44, 5.37±0.57 and 4.71±0.43, respectively) in ice cream produced by Looli factory. The present findings support the results of Marino (1954) and Keller et al. (1987) who suggested that fresh ice cream contained not more than 100,000 cfu/ ml of total bacteria counts. From the above findings, it was found that all ice cream samples were within the acceptable limit of public health safety because the samples did not exceed the total viable count (100,000 cfu/ ml) which were in agreement with that of Marino (1954); Hankin and Hanna (1984). Table (4-7): Average microbial quality of flavored from ice cream
machines:
Machine Sig. Microbial content Chocolate Vanillia Coconut Strawberry Mango level Total bacteria a bc ab ab ab count (log10 cfu/ 5.97±0.37 5.13±0.33 5.38±0.56 5.61±0.54 5.55±0.56 * gm) Yeast count 6.50±0.51a 6.03±0.44a 6.12±0.50 a 6.16±0.48 a 5.91±0.61 a NS (log10 cfu/ gm) Coliform count 5.22±0.46a 5.15±0.43a 4.90±0.37 a 4.78±0.25 a 4.90±0.47 a NS (log10 cfu/ gm) Psychrotrophic a a a a a count ( log10 cfu/ 4.22±0.44 4.14±0.34 4.35±0.55 4.26±0.55 4.09±0.54 NS gm)
Means within the each row bearing the similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
*: Significant: at (P< 0.05). Table (4-8): Average microbial quality of flavored ice cream samples
from Looli factory:
Looli Sig. Microbial content Chocolate Vanillia Coconut Strawberry Mango level Total bacteria ab bc a ab ab count (log10 cfu/ 5.15±0.51 5.06±0.65 5.33±0.46 4.92±0.36 5.12±0.47 * gm)
Yeast count (log10 6.38±0.59a 6.00±0.43a 6.64±0.44a 6.06±0.40 a 6.12±0.66a NS cfu/ gm)
Coliform (log10 5.07±0.55a 5.37±0.57a 4.75±0.24a 4.94±0.55 a 5.12±0.50a NS cfu/ gm) Psychrotrophic a a a a a count (log10 cfu/ 4.19±0.65 4.44±0.61 4.42±0.54 4.71±0.43 4.19±0.69 NS gm)
Means within the each row bearing similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
*: Significant: at (P< 0.05).
It is clear from the overall results that ice cream samples were of superior quality, because the counts of total bacteria were less than the recommended microbiological standard of food and Drug Administration and USPHA (1965). The results of the samples are consistent with that reported by
Tampieri and Dosseena (1967). His report showed that the ice cream contained > 10 coliform per ml. The coliform standards for ice cream should not exceeded 10/ ml (James, 1978).
4.3 Sensory characteristics of ice cream:
In evaluating the sensory characteristics (color, texture, flavor, taste and overall acceptability), ten untrained parameter on a scale ranging from 1 to 5 (Appendix 1).
Table (4-9) shows the mean sensory scare of ice cream made from different type of factory. The color score (P> 0.05) was highest in ice cream made by machines (6.73±0.69) compared with Looli ice cream (6.58±0.77). The highest mean of texture, flavor, taste and overall acceptability (P< 0.001) were obtained in Looli ice cream
(6.26±1.34, 6.29±0.73, 6.68±0.72 and 6.56±0.69, respectively), while the lowest mean were obtained in machines ice cream (3.39±1.52,
4.57±1.15, 5.06±1.23 and 5.15±1.17, respectively).
Table (4-9): Sensory characteristics of ice cream samples from Looli
factory and ice Machines:
Sensory Machines Looli Sig. level characteristics
Color 6.73±0.69 a 6.58±0.77 a NS
Texture 3.39±1.52 b 6.26±1.34 a ***
Flavor 4.57±1.15 b 6.29±0.73 a ***
Taste 5.06±1.23 b 6.68±0.72 a ***
Overall acceptable 5.15±1.17 b 6.56±0.69 a ***
Means within the each row bearing similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
***: Very highly significant: at (P< 0.001).
The present results were, in agreement with the findings of
Roland et al. (1999) who concluded that the sensory response to the ice cream samples was affected by the variation in fat content. Our data (Table 4-9) were also in agreement with the findings of Zheng
(1997) who reported that fat is important in food for sensory qualities such as flavor, color, texture and mouth feel. Our results were, in agreement with the findings of Noakes et al. (1996) who observed slightly color differences in daily products (milk, butter, cheese and ice cream) with a higher unsaturated fatty acid content.
Regarding sensory characteristics, Table (4-10) shows mean sensory score of ice cream made from different types of flavors. The color and overall acceptability of ice cream (P> 0.05) showed the best result in ice cream made from mango flavor (6.87±0.65 and
6.18±1.10) and the worst were in ice cream made from vanillia
(6.25±0.72) and coconut (5.44±1.18). The best texture score (P> 0.05) was found in ice cream made from strawberry (4.78±2.00), while the worst was found in coconut ice cream (4.27±2.07). Ice cream made from coconut (P< 0.01) and chocolate (P> 0.05) scored the highest flavor and taste (5.67±1.12 and 6.28±1.31, respectively), while the lowest score of flavor and taste were in strawberry (4.71±1.52 and
5.43±1.28). Table (4-10): Sensory characteristics of flavored ice cream:
Sensory Sig. Chocolate Vanillia Coconut Strawberry Mango characteristics level Color 6.68±0.84a 6.24±0.70a 6.74±0.64a 6.81±0.64a 6.87±0.65a NS
Texture 4.49±1.99a 4.46±2.34a 4.27±2.07a 4.78±2.00a 4.68±1.84a NS
Flavor 5.39±1.06ab 5.59±1.26ab 5.67±1.12a 4.71±1.52bc 4.92±1.40ab *
Taste 6.28±1.31a 5.57±1.51a 5.55±1.19a 5.43±1.28a 5.70±1.24a NS
Overall acceptable 5.77±1.24a 5.71±1.35a 5.44±1.18a 5.48±1.18a 6.18±1.10a NS
Means within the each row bearing the similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
*: Significant: at (P< 0.05).
The results were consistent with the findings of Parikh (1977) who mentioned that ice cream should have a delicate, attractive color suggest or is reading associated with the flavor. Moreover almost all flavors of ice cream should be slightly colored (Arbuckle, 1966). With respect to sensory characteristics, tables (4-11 and 4-12) show the mean sensory score of ice cream made from different flavors. The highest mean of color, taste and overall acceptability (P> 0.05) were obtained in chocolate (6.95±0.56), chocolate (5.85±1.50) and mango (5.80±1.26) in machines ice cream. However the highest score of color, taste and overall acceptability were found in strawberry (6.78±0.70), vanillia (7.18±0.67) and vanillia (6.93±0.63) in ice cream produced by Looli. The texture score (P< 0.01) and flavor (P< 0.05) were highest in ice cream machines made with chocolate (4.15±1.92) and vanillia (5.22±1.34) flavors in ice cream produced by machines. However that produced by Looli made with vanillia and coconut flavors revealed the highest score (6.88±0.68 and 6.60±0.73). The above result were generally, in agreement with the findings of Furia (1972) who proposed that flavor is the combination of taste, feeling and odor on receptors in the mouth and the nose. Our results were also in agreement with the findings of Arbuckle (1966) who showed the body and texture characteristics are closely associated and are important in influencing consumer acceptance of ice cream and related products.
Table (4-11): Flavor and sensory characteristics of ice cream from
machines:
Sensory Machines Sig. characteristics Chocolate Vanillia Coconut Strawberry Mango level Color 6.95±0.56 a 6.13±0.7a 6.82±0.65 a 6.83±64 a 6.93±58 a NS Texture 4.15±1.92 a 2.85±1.4bc 2.73±0.71bc 3.60±1.58ab 3.60±1.45ab ** Flavor 4.87±0.98ab 5.22±1.3a 5.05±0.87ab 3.67±0.91bc 4.05±0.88ab * Taste 5.85±1.50 a 4.50±0.7a 4.90±1.05 a 4.87±1.24 a 5.18±1.26 a NS Overall acceptable 5.38±1.32 a 4.90±1.0a 4.90±1.09 a 4.78±0.96 a 5.80±1.26 a NS
Means within the each row bearing the similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
*: Significant: at (P< 0.05).
**: Highly significant: at (P< 0.01). Table (4-12): Flavor and sensory characteristics of ice cream from
Looli factory:
Looli Sig. Sensory leve characteristics Chocolate Vanillia Coconut Strawberry Mango l Color 6.28±1.06 a 6.43±0.63 a 6.63±0.65 a 6.78±0.70 a 6.70±0.78 a NS Texture 5.00±2.11bc 6.88±0.68 a 6.58±0.84ab 6.55±1.00ab 6.30±0.95ab ** Flavor 6.18±0.60ab 6.15±0.92bc 6.60±0.73 a 6.28±0.51ab 6.23±0.92ab * Taste 6.93±0.63 a 7.18±0.67 a 6.53±0.54 a 6.28±0.81 a 6.48±0.73 a NS Overall acceptable 6.35±0.89 a 6.93±0.63 a 6.25±0.80 a 6.75±0.53 a 6.75±0.45 a NS
Means within the each row bearing the similar superscripts are not
significantly different (P> 0.05).
NS: No significant: at (P> 0.05).
*: Significant: at (P< 0.05).
**: Highly significant: at (P< 0.01).
CHAPTER FIVE CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions: From this study the following conclusions were drawn: 1. Flavor of ice cream showed non significant difference in fat, protein, ash and sucrose. 2. Total solids content was found to be significantly by the flavor of ice cream. 3. The processing techniques showed total bacteria count significantly increased in ice cream made by machines and slightly increased in ice cream made by Looli. 4. Yeast, coliform and psychrotrophic bacteria counts were not significantly affected by the type of producers. 5. Total bacteria and psychrotrophic counts were found not to be significantly affected by the flavor of ice cream, while coliform bacteria and yeast were significantly affected. 6. The processing techniques also affected the quality of the ice cream made as the best score values of texture, flavor, taste and overall acceptability were found in ice cream made by Looli samples, while the lowest values were found in machines samples. 7. The highest score values of color were found in machines samples, while lowest values were found in Looli samples. 8. Color, texture, taste and overall acceptability were not significantly affected by the flavor, while flavor was significant affected.
5.2 Recommendations:
The present study recommended the following:
1. Further investigation on some nutritional characteristics of ice
cream made from different raw materials.
2. Careful selection and testing of the raw materials, the use of
correct processing conditions, equipment should be properly
cleaned and adequately santitized and finally satisfactory
handling of the product at the sales point should be monitored.
3. Future work is needed to study various fat substitutes in ice
cream formulations and to evaluate the effects on the sensory
characteristics.
4. Sudan is a large country in the production gum Arabic; this
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Name…………………. Date …………………
Sample No. Color Texture Flavor Taste Acceptable
Key:
Excellent = 9.
Very good = 7.
Good = 5.
Fair = 3.
Poor = 1.
Comments: