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Author: Thapa, N ava, R Title: Effect of Tempering and Other Processing Treatments on the Anti nutritional Factors and a Canning Quality Attribute ofDark Red Kidney Beans The accompanying research report is submitted to the University of Wisconsin-Stout, Graduate School in partial completion of the requirements for the Graduate Degree/ Major: MS Food and Nutritional Sciences
Research Adviser: Cynthia Rohrer, Ph.D.
Submission Term/Year: Summer, 2012
Number of Pages: 71
Style Manual Used: American Psychological Association, 6th edition
I:8J I understand that this research report must be officially approved by the Graduate School and that an electronic copy of the approved version will be made available through the University Library website I:8J I attest that the research report is my original work (that any copyrightable materials have been used with the permission of the original authors), and as such, it is automatically protected by the laws, rules, and regulations of the U.S. Copyright Office. I:8J My research adviser has approved the content and quality of this paper.
STUDENT:
NAVATHAPA DATE: JULY, 2012
ADVISER:
CYNTHIA ROHRER, PhD DATE: JULY, 2012
1. CMTE MEMBER'S NAME: NA VEEN CHIKTHIMMAH, PhD DATE: JULY, 2012
2. CMTE MEMBER'S NAME: MARCIA MILLER-RODEBERG, PhD DATE: JULY, 2012
This section to be completed by the Graduate School This final research report has been approved by the Graduate School.
Director, Office of Graduate Studies: DATE: 2
Thapa, Nava R. Effect of Tempering and Other Processing Treatments on the Anti-nutritional
Factors and a Canning Quality Attribute of Dark Red Kidney Beans
Abstract
Kidney beans are an excellent source of proteins (20-30%), carbohydrates (50-60%) and fairly good sources of minerals, fibers and vitamins. Thus, they are important components of a healthy diet. However, their nutritional quality is indirectly impacted by the presence of heat labile and heat-stable antinutritional factors (ANF) that could exhibit undesirable physiological effects. The effect of tempering process alone and in combination with blanching, and soaking processes on the level of two antinutritional factors of beans, namely phytic acid and tannin, was studied. The phytic acid and tannins in dark red kidney beans ranged from 12.37 to 23.60 mg/g, and 0.11 to 28.78 mg/g, respectively. A reduction in the level of these antinutrients was observed after 12 different treatments. Out of 12 different treatment conditions used in canning process of beans, the 12 h tempering-soaking-blanching-canning process was found to be the most effective for the reduction of phytic acid (62%) and tannins (82%). This study also demonstrated that the percentage split of beans obtained from the tempered canned beans (11%) was found to be lower than the commercially soaked and processed canned beans (21%).
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Acknowledgements
I would like to recognize and express my sincere gratitude to a number of people that have contributed and helped me throughout this project. I would first like to thank Dr. Cynthia Rohrer for her tremendous help to my thesis completion. Without her continued guidance and support, I would have not been able to finish my master’s degree. I would like to thank Dr. Naveen
Chikthimmah for providing me valuable inputs for my research and for editing my thesis. I am also very thankful to Dr. Marcia Miller-Rodeberg for the valuable time and suggestions.
I would like to express my deep gratitude to Dr. Lamin Kassama for providing me direction, encouragement and countless effort to my thesis work. His continuous guidance, valuable ideas, and amazing mentorship brought this research into the real shape.
I would also like to thank UW-Stout Research Services for providing me student research grant and Chippewa Valley Bean Company for helping me in my research. I am also thankful to Dr.
Carol Seaborn, and Dr. Carolyn Barnhart for their continuous support.
I would like to offer my high regards to Biswas Palikhey and Prawesh Rijal for their great help in assisting me in data analysis and providing me valuable comments in my thesis. I am also thankful to Connie Galep, Bikram Upadhaya, and my other friends who helped me in the laboratory management and chemical analysis during the conduction of experiments.
Last, but not the least, I would like to show my sincere gratitude to my parents for their continued support, love and inspiration. 4
Table of Contents
...... Page
Abstract ...... 2
List of Tables ...... 7
List of Figures ...... 8
Chapter I: Introduction ...... 9
Statement of the Problem ...... 12
Purpose of the Study ...... 13
Objectives ...... 13
Definition of Terms...... 14
Limitations ...... 14
Chapter II: Literature Review ...... 15
History of Kidney Beans ...... 15
Application of Kidney Beans ...... 15
Importance of Dark Red Kidney Beans ...... 16
Nutritional Aspects of Beans ...... 16
Canning of Dry Beans ...... 18
Canning Technique for Preservation of Red Kidney Beans ...... 18
Standard Canning Procedure...... 19
Importance of Canned Beans ...... 20
Sensory Quality of Canned Beans ...... 20
Texture ...... 20
Color ...... 21 5
Visual Appearance ...... 22
Splitting ...... 22
Current Studies on Tempering of Beans ...... 23
Antinutritional Factors of Beans ...... 23
Phytic Acid...... 26
Tannins ...... 29
Chapter III: Methodology ...... 34
Sample Preparation ...... 34
Tempering ...... 34
Soaking ...... 35
Blanching ...... 35
Thermal Processing and Canning ...... 36
Phytic Acid Content ...... 36
Tannin Content...... 37
Splitting of Beans ...... 38
Moisture Content of Beans ...... 38
Statistical Analysis ...... 39
Chapter IV: Results and Discussion ...... 40
Moisture Content of Beans after Tempering and Soaking...... 40
Phytic Acid Content of Canned Beans...... 42
Tannin Content of Canned Beans ...... 48
Splitting of Canned Beans ...... 51
Chapter V: Conclusion ...... 56 6
Recommendations ...... 57
References ...... 59
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List of Tables
Table 1: Ranges in levels of antinutritional factors in dry beans……………...……………….…25
Table 2: Effect of various treatments on the phytic acid content of dark red kidney beans and subsequent reduction (%) in dark red kidney beans …………………………………………...…45
Table 3: Effect of various treatments on the tannin content of dark red kidney beans and subsequent reduction (%) in dark red kidney beans……………………………………………....50
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List of Figures
Figure 1: Structures of Phytic acid………………………………………………………….…..27
Figure 2: An example of hydrolysable tannins and related compounds…………………….….31
Figure 3: An example of a condensed tannin………………………………………………...... 32
Figure 4: Effect of tempering (45°C/95% R.H.) at 6 h, 12 h and 24 h on moisture content of beans soaked for 0, 1, 2, 3, 4 and 5 h, respectively...………………………………..……….…...... 41
Figure 5: Percentage split in canned beans with various treatment conditions ………...... 53
Figure 6: Canned beans obtained from commercial soaking and canning process (left) and canned beans obtained from tempering and canning process …………………………………………...54
Figure 7: Example of split beans after thermal processing due to high water uptake levels…………………………………………..………………………………………………….55
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Chapter I: Introduction
Dry beans are important source of protein throughout the world. Red kidney beans
(Phaseolus vulgaris L.) are one of the most important legumes of nutritional interest in the United
States. Per capita, bean use has been increasing in the USA, which is attributed to the increasing consumption trend in dry bean market due to nutritional awareness and to changes in the traditional American diet. Furthermore, increase in the Hispanic population has also significantly contributed to the increase consumption of beans in the U.S. It is reported that approximately 61% of the total dark red kidney beans are produced in Minnesota and Wisconsin as reported by
USDA, Agricultural Outlook (1999).
It is well recognized that legumes such as common beans, lentils, and kidney beans are the main source of supplemental protein based diets. Kidney beans are fairly good source of nutrients with 22.7% protein, 3.5% mineral matter, 1% fat, 5.1% crude fiber, and 57.7% total carbohydrates ( Khalil et al., 1986). However, the biological utilization (bioavailability) of the nutrients is interfered with various anti-nutritional factors present in legumes. These anti- nutritional factors coupled with indigestible bean proteins impede the absorption of the nutrients like calcium, iron, and zinc in the human gut. The removal of antinutritional factors can be a challenging process and requires treatment methods to reduce or remove the level of antinutrients in beans. Examples of treatment methods to reduce antinutritional factors include fermentation, germination, thermal treatments (Cooking) and soaking procedures (Abd El-Hady& Habiba,
2003; Martin-Cabrejas et al, 2004).
Soaking before canning may be one of the processes for removal of soluble antinutritional compounds, which can be eliminated by discarding the soaking solution. The purpose of soaking before canning is to remove foreign material, facilitate cleaning, aid in can filling through uniform 10 expansion, ensure product tenderness and to improve color (Loggerenberg, 2004). During soaking, dry beans increase 80 % in mass and reach 53 – 57 % final moisture content. Water uptake (caused by diffusion) takes place during soaking, causing the beans to soften and swell
(Wang et al., 1988). Soaking beans before cooking would also accelerate the cooking rate
(Loggerenberg, 2004).
Blanching is the immersion of foods into hot water (80 to 100°C) or steam for several minutes. The main purpose of blanching is the inactivation of enzymes, which might produce off- flavors’, but also to soften the product and remove gases to reduce strain on can seams during retorting (Jones & Beckett, 1995). The blanching process is also responsible for the removal of dry bean flavor and odor (Loggerenberg, 2004).
Another process during canning is thermal processing. De Lange (1999) heat sterilized canned beans in a vertical autoclave at 121.1°C for 50 min. Bolles et al. (1990) sterilized at
121.1°C for 30 min, also using a vertical autoclave. Sterilizing beans at 115.6°C for 35 min or
121°C for 15 min in the presence of CaCl2 and EDTA (Ethylene diamine tetra acetic acid) containing brine resulted in optimal sterilization values, reduction of trypsin inhibiting activity and bean firmness values (Wang &Chang, 1988).
Tannins in beans are any naturally occurring phenolic compounds with molecular mass of
500 to 3,000 that contain 1 or 2 phenolic hydroxyl or other suitable groups per 100 MW, which enables it to form cross-linkages to proteins and other macromolecules (Loggerenberg, 2004).
These heat resistant substances, which are not destroyed by cooking, interfere with the physiology and utilization of nutrients by the animal (Sgarbieri, 1989). This is caused by the cross-linkages of tannins to protein, which leads to low protein digestibility and availability in dry beans
(Loggerenberg, 2004). Tannins may also interfere with the biological utilization of minerals and 11 certain vitamins, but the importance of these reactions has not yet been identified (Sgarbieri,
1989).
Phytic acid is a chelating agent, which might lower the bioavailability of minerals, such as
Zn, Mn, Cu and Fe. Although phytic acid is regarded as an antinutritional factor in beans, the phytic acid phosphorous content of red kidney beans is an indicator of cookability. This is because phytic acid favors a more rapid rate of dissolution of pectic substances in beans during cooking (Loggerenberg, 2004).
One of the major quality attributes in canned beans is splitting. Splitting of cooked beans is one of the factors that determine the intactness of cooked beans, and is often determined subjectively (Hosfield, 1991). Beans that appear intact before canning might also develop large percentages of splits during retort processing, causing the product to be unappealing and may lead to price reductions. In addition, not only would splitting of canned beans result in the exudation of starch into the canning medium, causing graininess of the sauce. Splitting could also lead to clumping of individual beans (Loggerenberg, 2004). Starch material might also be deposited on the bottom of the can and thereby reduce the quality of the canned product (Forney et al., 1990).
Splitting might even lead to a complete breakdown of beans. In small white beans a larger percentage of split beans would be more tolerable than in larger beans, such as kidney and pinto beans (Loggerenberg, 2004).
The objective of this research was to compare the reduction of phytic acid and tannins in canned beans by using a tempering technique with processing treatments including soaking, blanching and thermal processing. Measured canning quality attributes were: splitting, phytic acid, and tannin content. 12
The tempering process was conducted in an environmental chamber at a predetermined relative humidity and temperature. Tempering prior to thermal processing was hypothesized to contribute to reducing the level of anti-nutritional factors. The anti-nutritional factors of dark red kidney beans were determined before and after the canning process using a spectrophotometric method.
Statement of the Problem
A significant number of world populations rely on legumes and cereals as their staple foods.
Legumes are often advocated in Western diets because of their nutritional benefit and are relatively inexpensive compared to other sources of protein (Borade et al., 1984). Red kidney beans (Phaseolus vulgaris L.) are one of the most important legumes of nutritional interest in the United States.
The health-related benefits of beans include their positive effect on lowering the blood cholesterol and glucose levels (Walker, 1982; Leeds, 1982), because of their high dietary fiber content. However, they are under-consumed because of the presence of antinutritional compounds, such as enzyme inhibitors (trypsin, chymotrypsin, α-amylase), phytic acid, flatulence factors, tannins and lectins (Lyimo et al., 1992). In both human and animal nourishment, phytic acid is considered to be an antinutrient because of its negative effect on the absorption of zinc, iron, copper and calcium (Van der Poel, 1990).
Tannins are one of the several anti-nutritional factors present in beans that lower the nutritional quality of beans (Vincent et al., 1981).
Adopting simple processing methods like soaking, blanching and cooking may be able to reduce the anti-nutritional concentration in beans (Yasmin et al., 2008). Soaking is a pretreatment process that requires significant amount of time prior to cooking. Thus, soaking as a pretreatment prolongs the process time in processing of beans. Research done by Thapa, Juliech & Kassama
(2009) observed that a tempering process reduced soaking time by 12h during the pretreatment of 13 beans prior to the canning process. The current research focused on the effect of tempering to minimize the antinutrients prior to cooking.
Purpose of the Study
The quality characteristics and anti-nutritional factors in dry beans has been an area of research relevance. Major quality attributes such as bean splitting during thermal processing may be reduced by a tempering process. Previous preliminary research shows the importance of a tempering process to achieve reduction in bean splitting during canning. Tempering alters bean structure, which may also improve physical appearance of the canned bean by minimizing splitting and increasing firmness. There is a scarcity of research information in the area of canning pretreatments to reduce bean splitting. No research information exists in the literature on the reduction of anti-nutritional factors of kidney beans using a tempering process of 12h and 24h at
45°C and 95% R.H. This study is therefore done to gain research based information to develop bean pretreatments.
Objectives
The main objective of this research was to study the effect of tempering on the antinutrient content and quality (splitting) of canned red kidney beans. These parameters were studied before and after the canning process. The specific objectives were as follows:
Objective-1: Determine the effect of the tempering process on reducing the splitting of thermally processed red kidney beans.
Objective-2: Investigate the effect of the tempering process on tannins and phytic acids in canned dark red kidney beans. 14
Definition of Terms
The following terms are important in understanding this study and will be used commonly throughout this research paper and are defined as follows.
Tempering of Beans. To bring to a desired consistency, state or other physical condition by the application of heat and relative humidity.
Canning. Method of sterilizing food by heat in hermetically sealed (airtight) containers, which allows ready to eat foods that are neither frozen nor dehydrated to remain safe and wholesome during months or even years of storage at room temperature without the use of additives or preservatives.
Anti-nutritional Factors. Natural or synthetic substances found in the human diet or animal feed that have the potential to adversely affect health and growth by preventing the absorption of nutrients from food.
Limitations
In this study only one condition of environmental chamber was used to study the effect of tempering on the canning quality of red kidney beans. Further studies of quality characteristics of canned kidney beans should be done. A comparative study of tempering and soaking process could be carried out to judge the effectiveness of canning process. Also the antinutrients analysis may be done with advanced analytical techniques to enhance accuracy.
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Chapter II: Literature Review
This chapter will include an in-depth discussion on history, applications and the canning techniques for the preservation of red kidney beans, followed by a discussion of canning quality parameters, and tempering of beans.
History of Kidney Beans
Dry beans (Phaseolus spp. L.) are the most important grain legumes for human consumption. Dry beans have been cultivated for thousands of years, and have been played an important role in the traditional diets of many regions throughout the world (Zamindar et al.,
2011). Beans are less significant in western diets compared to most of the developing countries.
The daily per capita consumption of all bean products is 9 g in the United States compared to about 110 g in Asia (Boateng et al., 2008).
The kidney bean, also known as Phaseolus vulgaris L., was cultivated about 7,000 years ago in Southwestern Mexico. Kidney beans gained wide acceptance during the history of
Americas before the appearance of significant European influences on the American continents
(Pre-Columbian period). Early chroniclers indicated that great importance was given to this species in the Aztec and Incan empires. The people of Axocopan used dry beans to pay tributes at the early colonial period in North America (Wu, 2002).
Application of Kidney Beans
Beans play an important role in human diet in Africa, Latin-America and Asian countries, improving the nutritional status of many low income populations (Milan-Carrillo et al., 2007).
Beans contain two or three times more proteins than cereals and offer a more practical way of eradicating protein malnutrition than cereal based diets (Carmona-Garcia et al., 2007). 16
Kidney beans are consumed as cooked dried beans or canned beans (cooked, baked or refried).
Also they are used in the fruit and vegetable processing industry in the production of frozen or canned food. Beans are highly nutritious food able to complete with meat. In the western hemisphere, kidney beans are used in salads, soups and other food products (Kahlon et al., 2005).
Importance of Dark Red Kidney Beans
The dry bean is an important source of protein, dietary fiber, iron, complex carbohydrates, minerals, and vitamins for millions of people in the world. It is one of the basic food categories in the diet of the indigenous populations in South America, Asia and Eastern/Southern Africa. The per capita dry bean consumption has been increasing in the United States in the past 20 years.
Factors contributing to this continuous trend in the dry bean market include the increasing awareness and changes in the traditional American diet, an increase in immigration of Hispanic population, and the increasing interests in ethnic foods featuring dry beans. According to the
Continuing Survey of Food Intakes of Individuals, complied by USDA’s Agriculture Research
Service, about 4% of the population consumes kidney bean on any given day, which is among the highest of any dry bean consumption (Lucier et al., 2000; Belshe et al., 2001).
Nutritional Aspects of Beans
Beans (Phaseolus vulgaris L.), are excellent sources of proteins (20-30%) and carbohydrates (50-60%) and fairly good sources of minerals and vitamins (Rehman & Shah 2004;
Yin et al., 2008). Dry beans are widely known for their fiber, mineral and protein contents. The flour and protein concentrate of red kidney bean exhibited good functional properties (Tang,
2008). About 80% of the total proteins found in dry beans are storage proteins. These proteins supply the young seedling with nitrogenous compounds and amino acids. Dry beans are deficient in sulphur-containing amino acids such as methionine, cysteine and have small deficiencies in 17 valine, leucine, isoleucine and threonine. All dry beans are good sources of lysine, indicating that dry beans could be added to lysine-deficient cereal products (Loggerenberg, 2004).
Resistant starch is important due to its various beneficial health properties mostly mediated by short chain fatty acids produced during its fermentation in the large intestine.
Legumes contain higher amount of resistant starch in comparison to cereals and tubers (Yadav et al., 2010). The merit of dry bean is its high caloric value and protein content. Ramirez-Cardenas et al. (2008) pointed out that low concentrations of phytates and phenolic compounds (which are present in beans) can be protective against cancer and cardiovascular diseases. Also fermentation of oligosaccharides present in beans may result in the production of short chain fatty acids and decrease in intestinal pH (Fernandes, et al., 2010).
Beans are the rich source of B vitamins, folate, riboflavin and valuable mineral substances like potassium, calcium, magnesium, phosphorus and iron salts (Souci, Fachmann, & Kraut,
2000). Thus, they are important components of a healthy diet. However, their nutritional quality is indirectly impacted by the presence of heat labile and heat-stable antinutritional factors (ANF) that exhibit undesirable physiological effects (Pusztai, et al., 2004). The ANFs are structurally different compounds broadly divided into two catergories: proteins (such as lectins and protease inhibitors) and others such as phytate, tannins or proanthocyanidins, oligosaccharides, saponins and alkaloids. In general raw beans contain far higher levels of ANFs than their processed forms hence processing is necessary before the incorporation of these grains into food or animal diets
(Hajos and Osagie, 2004). Few studies about the industrial process of dehydration after soaking and cooking treatments have been carried out in order to investigate the nutritional improvement of beans (Martin-Cabrejas et al., 2006).
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Canning of Dry Beans
Canning is the heat sterilization process in which product is placed in hermetic container, heated at sufficiently high temperature for a sufficient length of time to destroy all microbial and enzyme activity (Loggerenberg, 2004). Properly sealed and heated canned foods should remain stable and indefinitely unspoiled in the absence of refrigeration. The sealing step is critical and heat is applied under pressure for a specific temperature-time combination. The latter is determined by the type of food, pH, container size and consistency or bulkiness of the food, but heating of food for longer than necessary is undesirable, as the nutritional and eating quality of food are affected negatively by prolonged heating (Brock et al., 1994).
Canning Technique for Preservation of Red Kidney Beans
Canning technique was invented by Nicholas Appert, a Frenchman who successfully developed this food preservation technique, for almost two centuries. Nowadays canned foods have become widely accepted in daily lives. Canned foods provide a convenient food style free from food spoilage and natural deterioration with a longer shelf life. The thermal processes greatly enhance the palatability of the edible dry beans, inactivate toxic factors, and increase the nutritional availability and digestibility of different nutrients. The current research also shows that thermal treatment can reduce heat-labile antinutritional factors and increase the digestibility of protein and amino acid in raw edible beans (Phaseolus vulgaris L.) thereby increasing the nutritive value of beans (Wu et al., 1994). However, excessive cooking may introduce reduced protein utilization and increased mineral loss (Wu, 2002)
Standard Canning Procedure
Canning of beans is mainly composed of two processes, namely the soaking /blanching process and thermal processing/heat sterilization. The purpose of soaking before canning is to 19 remove foreign material, facilitate cleaning, aid in can filling through uniform expansion, ensure product tenderness and to improve color (Loggerenberg, 2004).
Industrial canners make use of either a long/cold or short/hot soaking process. With the former, soaking takes place for 6 to 20 h, changing water every 4 to 6 h to prevent bacterial activity. Cold soaking is followed by blanching in continuous rotary water blanchers at approximately 90-95oC for 5 min. The overnight soaking process has the following disadvantages: It is a lengthy process, difficult to control swelling and microbiological stability and germination could take place, resulting in worm-like material in the beans if broken off during further processing. Hot soaking takes place in slowly running continuous blanchers or pipe blanchers, where product heating takes place at 85 – 90 °C for 30 min. The main disadvantage of this process is that the product does not become as tender as in the case of slowly hydrated beans
(Loggerenberg, 2004).
The blanching process is responsible for the increase of bean moisture content to the final
50 – 55 % and the removal of dry bean flavor and odor. Blanching is the immersion of foods into hot water (80 to 100°C) or steam for several minutes whose purpose is the inactivation of enzymes (Loggerenberg, 2004).
In heat sterilization canning process, soaked blanched beans are filled into a can, hot sauce added (95oC), and the can seamed and heat sterilized immediately. Sterilization is done in static retorts, agitating retorts or hydrostatic sterilizers. Rotation increases the rate of heat transfer, thereby reducing processing time and the gelation tendency of the sauce. Canning time varies, depending on the size of the cans and the operational temperature. A No.2 ½ can require 45 minutes at 116°C. High temperature not only kills the microbes, but also completely tenderizes 20 the beans. The canned beans are immediately cooled by water bath to a temperature of 35° to
41°C. They are then ready to be labeled and shipped (Loggerenberg, 2004).
Beans are further hydrated during the thermal process. Equilibration with brine or sauce takes 2-4 weeks after canning. The final moisture content of the canned beans ranges from 65-
70% (Uebersax, Ruengsakulrach & Occena, 1991).
Importance of Canned Beans
Canned products from kidney beans such as refried beans, soups and baked beans, are very commonly available for consumers. Many people look for beans with rapid expansion ability, higher drained weight, ease in cooking, and uniformity after the thermal process. The major characteristics responsible for canning quality of beans are the physical characteristics of the seed, processing and cooking characteristics and chemical composition of beans (Wu, 2002)
Organoleptic properties within the final canned products are considered to be one of the major quality evaluation standards. However, not all the cultivars are blessed with equally acceptable quality. The problems affecting consumer’s preference are often related to the occurrence of bean discoloration, hardness of the beans and breakage of the seed coat after the canning process (Wassimi et al., 1990). When the seed coat splits, it affects more than just the appearance, since this splitting can also result in starchiness and excessive viscosity in the final product. The excessive viscosity is due to the graininess of the sauce and clumping of individual beans which make the canned product unacceptable to consume. The beans must still maintain their individual integrity in the canning medium (Loggerenberg, 2004).
Sensory Quality of Canned Beans
Texture. Texture is used as an indication of the degree of consumer acceptance of canned beans as it affects the perceived stimulus of chewing. Texture, which is measured by a shear 21 press, is an indication of the firmness of beans and is measured as kg force required to shear 100 g of beans. The shear press ignores other kinesthetic perceptions such as viscosity, gumminess and adhesion. The higher maximum peak in height indicates firmer beans. Consumers usually rate texture of beans from “too soft” or “mushy” to “too firm / tough” or “hard” (Loggerenberg, 2004).).
Texture is influenced by bean temperature. Shear values of beans decrease as the temperature of canned beans on evaluation increases. These firmer textures at lower evaluation temperatures could probably be the consequence of gelatinization or retrogradation of bean starch.
Bean firmness after cooking relates to the phytin, calcium, magnesium, and free pectin levels, while the thickness of the palisade layer of the seed coat, as well as the lignin and alpha-cellulose in the seed coat also play a role in firmness. Hence, beans should be softened to certain limit during its processing to maintain its individual integrities that help to increase the product quality
(Loggerenberg, 2004).
Color. Color of food is caused by the absorption of more light at some wavelengths by pigments. Color is one of the properties of beans that consumers have specific preferences about
(Hosfield, 1991). The color of dry and cooked beans is usually measured with a HunterLab color meter (Hunter Associates Laboratory Inc., Reston, VA). The L-value indicates white to black, a- value indicates red to green and b-value indicates yellow to blue (Chung et al., 1995).
Bean which was processed 115.6 °C for 45 min and 121.1 °C for 30 min had no significant influence on the color of processed beans (Bolles et al., 1990). Soaking or cooking times affected the redness (b-values), while storage under unfavorable conditions that would cause hard-to-cook beans reduced the lightness character of beans (Paredes-López et al., 1991).
Beans canned without soaking pre-treatment are significantly darker in color than those that received a soaking treatment (Occena et al., 1992). Generally, the more intact the seed the greater the surface reflection would be, resulting in brighter appearing beans. The same was found by 22
Wang et al. (1988) when EDTA and CaCl2 were added to the brine. EDTA chelates free metal ions that would cause the formation of color complexes. The tannin content is one very important factor, which affects the darkness in color of uncooked dry beans. So it is more likely to have higher tannin content in darker beans (Loggerenberg, 2004).
Visual Appearance (VA). Visual appearance is one of the preferences of consumers of beans, which is determined subjectively (Hosfield, 1991). Visual appearance of canned beans is an evaluation of the general suitability of beans for commercial processing. Beans are evaluated for intactness, splits, free seed coats and brine consistency (Balasubramanian et al., 1999)
Splitting. Splitting of cooked beans is one of the factors that determines the intactness of cooked beans, and is determined subjectively. Beans that appear intact before canning might also develop large percentages of splits during retort processing, causing the product to be unappealing and may lead to price reductions (Loggerenberg, 2004). Not only would splitting of canned beans result in the exudation of starch into canning medium, causing graininess of the sauce, but could also lead to clumping of individual beans (Lu & Chang, 1996).
Splitting is also reduced in canned beans by the addition of calcium to the canning medium. Beans that contain a greater mass, due to greater water uptake levels, have a larger tendency to split (Forney et al., 1990). Van Buren et al. (1986) found that firmer beans would have fewer splits due to swelling that is generally caused by placing bean skins under pressure causing them to rupture. Larger sized beans would take up less water during canning, due to a larger volume-to-surface ratio, with consequential lower split values. The addition of CaCl2 to the brine reduces splitting and clumping of canned navy and pinto beans (Loggerenberg, 2004).
Splits were determined as the actual percentage of split beans found in a sample, as was recommended by industry. Only completely broken beans and loose skins were considered as 23 splits. The actual percentage of splits is determined by canning 100 seeds and calculating the percentage broken seeds after canning (Loggerenberg, 2004).
Current Studies on Tempering of Beans
A very few studies has been conducted on beans using the tempering process. The use of a tempering process is the art of food preparation and more particularly to an improved method for preparing a reconstitutable, dehydrated refried bean product containing whole beans as well as crushed beans (Thapa, Juliech & Kassama, 2009). The process of tempering is significant to achieve the desired condition of beans before canning. The tempering is the process of treatment in high temperature and high humidity. Tempering of beans at 95% relative humidity and at 45°C for 6, 12 and 24 hours in environmental chamber significantly decrease the soaking time (Thapa et al., 2009). High relative humidity tempering of red kidney beans reduces the soaking time to a relatively short time frame and allow for a more environmentally friendly technique by discharging less amount of waste water than the conventional method of soaking (Thapa et al.,
2009). The industrial canner soaks for 6-20 h to get the fully hydrated beans while the conventional method includes overnight soaking at room temperature that has the disadvantages of lengthy process and uncontrolled swelling( Loggerenberg, 2004). Hence, the process developed by Thapa et al. (2009) reduces the soaking time by 12 to 14 h. Based on this optimized process this paper attempts to evaluate the level of antinutrients and splitting percentage in kidney beans before and after the tempering and canning process.
Antinutritional Factors of Beans
Legumes contain toxic substances, such as trypsin inhibitors, phytohaemagglutinins
(substances agglutinating and destroying red blood cells), factors causing lathyrism and favism, cyanogenic factors, goitrogenic factors, saponins and alkaloids. These compounds adversely 24 affect enzyme activity, digestibility, nutrition and health, but many of them could be inactivated or eliminated by particular processing procedures, such as dehulling, pre-soaking and diffusion, sterilization, steaming and cooking (Loggerenberg, 2004). Some important antinutritional factors are tannins, phytic acid, trypsin inhibitors and hemagglutinin which are also listed in the table 1.
According to this table the tannin content in different varieties of Phaseolus vulgaris varies from
0.11 to 28.78 mg catechin equivalent g-1, while the phytic acid varies from 12.37 to 27.60 mg g-1.
Higher the amount of tannins and phytic acid, lower will be the nutritional value in beans. The table 1 also shows that the lower concentrations of trypsin inhibitor and hamegglutinin which also reduce the nutritional quality of dry beans.
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Table 1.
Ranges in levels of antinutritional factors in dry beans
Observations Content
Minimum Maximum
Tannins
Cowpea varieties (mg.g-1) 1.03 1.96
Four Phaseolus vulgaris
varieties (mg catechin
equivalent.g-1) 0.11 28.78
Trypsin-inhibiting activity
(TUI×10-3.g-1 protein) 4.77 27.98
Phytic acid
Four dry bean varieties
(mg.g-1) 12.37 23.60
Soybean, navy and
northern beans (mg.g-1) 10.00 12.00
Hemagglutinin
Four dry bean varieties
(HU×10-3.mg-1) 0.40 6.98
References: (Giami & Okwechime, 1993; Barampana & Simard, 1993; Elkowicz & Sosulski,
1982)
26
Phytic Acid
Phytic acid (PA, myo-inositol hexakisphosphate, IP6) was first identified in 1855 (Figure
1). It is a natural plant compound with a unique structure that is responsible for its characteristic properties. Phytic acid has 12 replaceable protons, allowing it to complex with multivalent cations and positively charged proteins and thus can be found in many forms. Phytate is the calcium salt of PA and phytin is the calcium/magnesium salt of PA. Phytic acid can exist as free acid, phytate, or phytin according to physiological pH and the metal ions present. All of these forms have been used interchangeably in most of the literature linked to phytic acid systems. Complete hydrolysis of phytic acid results in inositol and inorganic phosphates. Phytic acid phosphorus constitutes the major portion of total phosphorus in several seeds and grain. It accounts for 50-80% of the total phosphorus in different cereals and legumes. The phytic acid content is influenced by cultivar, climatic conditions and year. The accumulation site of phytic acid in monocotyledonous seeds is the aleurone layer, particularly the aleurone grain. Aleurone grain contains two types of inclusions: (a) globoids containing high amount of phytates, and (b) protein carbohydrate bodies
(Oatway, 2001).
27
Figure 1: Structure of Phytic acid
The association of phytate with proteins begins in seeds during ripening, when phytate accumulates in the protein-rich aleurone layer of cereals and protein bodies of legumes. Although the fine structure of phytate-rich particles in plants has been intensively studied, the nature of the interaction of proteins in such organelles with phytic acid is practically unknown. The formation of globoid crystals and their size is highly dependent on the presence of inorganic cations. Higher amounts of magnesium and calcium favor the formation of large globoid crystals (Oatway, 2001).
This fact suggests that higher concentrations of divalent cations increase phytate-phytic acid interactions rather than protein-phytic acid interactions. The conditions of processing such as addition of water, heat treatment (baking, autoclaving, extrusion etc), isolation and separation, action of phytate degrading enzymes (e.g.phytates, phosphomonoesters) may cause changes in the intensity and character of interactions. 28
The interaction of phytate with proteins, vitamins, and several minerals is considered to be one of the factors that limit the nutritive value of dry beans. Numerous studies suggest that phytate reduces the biological availability of dietary copper and manganese, iron, magnesium, and zinc. Phytate is also suggested to interfere with protein metabolism and to decrease the utilization of proteins subjected to proteolytic digestion (Loggerenberg, 2004).
Phytic acid has been shown to be bioavailable in cattle and other ruminants. At least 90% of phytate P in concentrates was hydrolyzed in vitro after inoculation with ruminal fluid from a lactating dairy cow. Less than 5% was recovered in excreta (Oatway, 2001). Most of this degradation is due to 3-phytase characteristic of microorganisms and takes place almost entirely in the rumen. Phosphorus of plant origin, mainly phytic acid, is generally considered to be poorly available for utilization by monogastric animals, including pigs, poultry, and fish. It is usually ignored in animal diet formulation as unavailable. Total phosphorus available from a feed ingredient is equivalent to non-phytate-phosphorus plus digestible phytate-phosphorus.
Availability of phosphorus from phytate ranged from 20 to 60%. It is important to determine how much P is available to minimize loss of nutrients to the environment. Excess P and other nutrients are excreted by the animal; 65–75% of the total P in formulated diets with supplemental inorganic
P is excreted in the manure (Oatway, 2001). This creates an environmental problem when the animal waste is left on farmland. A recent water quality assessment showed that P often exceeded water quality guidelines in high and medium intensive agriculture areas (Anderson et al., 1998). It is imperative that phytic acid be degraded in the animal to enhance the mineral and phosphate utilization by the animals and to decrease the pollution of groundwater by P.
The phytate molecule is negatively charged at physiological pH and is reported to bind with essential nutritionally important divalent cations such as Fe2+, Zn2+, Mg2+ and Ca2+…. 29 etc., and forms insoluble complexes, thereby making minerals unavailable for absorption. It also forms complexes with proteins and starch and inhibits their digestion (Oatway et al., 2001). The dephosphorylation of phytate is a prerequisite for improving nutritional value because removal of phosphate groups from the inositol ring decreases the mineral binding strength of phytate. These results increased bioavailability of essential dietary minerals (Sandberg et al., 1999). Overall, a good balance of nutrients is important for both animals and humans.
The total amount of any substance is not as important as the amount that is readily available for utilization. Any deficiency, excess, or imbalance in minerals or other nutrients can have a negative effect on health. PA has been shown to have many beneficial effects and it is tempting to recommend increasing PA intake to reap some of these benefits. However, any use of phytates as a therapeutic agent needs to be carefully considered because of the adverse effects associated with large intakes. Precautions must be taken to avoid mineral and trace element deficiencies (Oatway, 2001).
Tannins
Tannins are ubiquitous in nature and although a lot of attention has been given to their study, the term “tannin” continues to be difficult to define precisely. Indeed, whereas related phenolic compounds such as simple phenolics, neolignans and flavonoids are characterized and classified according to their chemical structure, tannins are a diverse group of compounds that are related primarily in their ability to complex with proteins (Fahey & Jung, 1989). Thus, tannins are usually defined as water-soluble polyphenolic substances that have high molecular weight and that possess the ability to precipitate proteins. Tannins have diverse effects on biological systems because they are potential metal ion chelators, protein precipitating agents, and biological antioxidants. Because tannins can play such varied biological roles and because of the enormous 30 structural variation among tannins, it has been difficult to develop models which allow accurate prediction of the effects of tannins in any system (Loggerenberg, 2004).
Tannins are high molecular weight, phenol-rich polymers that exist in many foods, including dry beans, and some examples are beverages, cereals, fruits, coffee and tea. Tannins are divided into two major types, condensed and hydrolysable. Hydrolysable tannins are polyesters of phenolic acids such as gallic acid, digallic acid (gallotannins) or hexahydroxydiphenic acid
(ellagitannins) and D-glucose or quinic acid, the latter serving as a polyalcohol core shown in
Figure 2. Hydrolysable tannins receive their name because they are readily cleaved by enzymes
(i.e. Penicillium tanninase) as well as by dilute acid to give a sugar such as glucose and a phenolcarboxylic acid such as gallic acid. On the other hand, condensed tannins are composed of flavan-3-ols linked via carbon-carbon bonds that produce anthocyanidins upon treatment with acidic alcohol as in Figure 3 (Rolando, 1999).
Condensed tannin concentration in plant tissue has been shown to vary with many factors.
These include plant species, plant part, plant maturity, growing season and soil fertility. Anuraga et al. (1993) observed that a combination of moisture stress and high temperature can resulted in an increase in the concentration of condensed tannins in plants. A dramatic change in condensed tannin concentration is due to the changes in soil fertility (Rolando, 1999).
31
COOH COOH
OH
Hexahydroxydiphenic acid
G OG
Penta-O-galloyl-/3-D-gluco.se I OG
Hydrolysable tannin
Figure 2. An example of hydrolysable tannins and related compounds; G = gallic acid.
Adapted from (Mangan, 1988) and Mueller-Harvey & McAllan (1992). 32
Figure 3. An example of a condensed tannin. Adapted from Mueller-Harvey & McAllan (1992).
The tannins of different plant species have different physical and chemical properties and therefore they have very diverse biological properties. The high affinity of tannins for proteins lies in the formers’ great number of phenolic groups. These provide many points at which 33 bonding may occur with the carbonyl groups of peptides. The formation of such complexes is specific, both in terms of the tannin and protein involved, the degree of affinity between the participating molecules residing in the chemical characteristics of each (Rolando, 1999). With respect to tannins, the factors promoting the formation of complexes include their relatively high molecular weight and their great structural flexibility (Mueller-Harvey & McAllan, 1992). The proteins that show the most affinity for tannins are relatively large and hydrophobic, have an open, flexible structure and are rich in proline. The complexes formed between tannins and proteins or other compounds are generally unstable. The bonds uniting them continually break and re-form (Mueller-Harvey & McAllan, 1992). The complexes that could come through four types of bond: 1) hydrogen bonds (reversible and dependent on pH) between the hydroxyl radicals of the phenolic groups and the oxygen of the amide groups in the peptide bonds of proteins, 2) by hydrophobic interactions (reversible and dependent of pH) between the aromatic ring of the phenolic compounds and the hydrophobic regions of the protein, 3) by ionic bonds
(reversible) between the phenolate ion and the cationic site of the protein (exclusive to HT), and
4) by covalent bonding (irreversible) through the oxidation of polyphenols to quinones and their subsequent condensation with nucleophilic groups of the protein (Rolando, 1999). For a long time it was believed that the formation of tannin-protein complexes was owed mainly to hydrogen bonds. However, it is now known that hydrophobic interactions are important.
34
Chapter III: Methodology
This chapter includes a discussion on the methods of sample preparation, chemical analysis and data analysis. It also comprises the process of raw material acquisition, instrumentation, and data collection procedure.
The red kidney bean, because of its hard nature, is difficult to cook. Therefore, in the food industry the canning process of red kidney beans requires a long soaking process in order to soften the seeds prior to cooking for enhancement of the bean quality. The advantages of soaking of bean includes increased yield of whole beans, tenderness level improvement, and uniform bean expansion in the can during processing. In an industrial practice, the soaking process takes about
6 to 18 h with intermittent water changing every 4 to 6 h to prevent bacterial activity. This current research utilized the environmental chamber for tempering of beans.
Sample Preparation
Red kidney beans used for the experiment were provided by the Chippewa Valley Bean
Company (Menomonie, Wisconsin). Beans were stored at room temperature (72°F) in cardboard boxes until they were processed for tempering. Beans of the same size were used in this research.
The smallest, largest and broken seeds were further removed manually. Beans were treated with different processes like tempering, soaking, blanching and thermal processing for canning.
Canned beans processed at specific time and treatment condition were prepared at the Department of Food and Nutritional Sciences, University of Wisconsin-Stout.
Tempering. The complete tempering process of red kidney bean was carried out in an
Environmental chamber (EC) (ESPEC model EWPA 647-4WWL, Hudsonville, Michigan).
Kidney beans were tempered in the environmental chamber at 45°C and 95% Relative Humidity
(RH). Three sets of bean sample each 600 g were tempered in EC for 6, 12 and 24 h. At specific 35 length of time in EC, the beans were soaked in water of 24°C for 0, 1, 2, 3, 4 and 5 h. The beans which were tempered only for 6 hours were not porous, and had moisture content of 30-40% after soaking for 4-5h. Therefore, due to the inadequate swelling of beans and low hydration coefficient, the tempered beans for 6 hours were not used for further canning process (Thapa et al., 2009).
Soaking. The beans which tempered for 12 h and 24 h were soaked for 2 h to achieve adequate moisture content (50-65%) required for the canning (Loggerenberg et al., 2004). Some samples were further soaked and blanched to evaluate the overall effect on the quality and anti- nutritional factors. To work on a commercial canning condition, one sample of untempered beans was soaked overnight in distilled water at room temperature. Based on the type of sample, the beans were soaked in small plastic buckets. The mass of the soaked beans were then obtained or further treated for blanching. Blanching was carried out in order to shorten the hydration time of beans.
Blanching. In the blanching process, dry beans samples were cooked in distilled water at
85°C for 8 minutes in electric oven in aluminum pan and then drained for can fillings. Broken or split beans resulting from soaking and blanching were removed while completely hydrated and firmer beans were selected for canning.
The canning medium was made with the following composition; CaCl2 = 0.42 g/L, NaCl =
27.24 g/L and sugar = 74.60 g /L (Van Buren et al., 1986). Calcium chloride was added to increase the firmness of beans. An increase in calcium content in brines also helps to enhance the lightness of canned beans. The NaCl helps to maintain the individual integrity of canned beans, while the EDTA chelates free metal ions that caused the formation of color complexes
(Loggerenberg, 2004). 36
Thermal Processing and Canning. The soaked and blanched beans (soaked beans equivalent to 96 g of dry sample used) were transferred to cans of size # 303, and filled with brine canning medium. The cans were sealed in Dixie automatic can sealer (Dixie Canner Co, Athens,
GA, USA). The sealed cans were then heat sterilized in a vertical autoclave (Loveless manufacturing Co, OK) at 240°F/10 psig for 40 minutes followed by instant cooling. After canning, a storage period of two weeks was allowed for the beans and the moisture in the brine medium to reach equilibrium (De Lange, 1999). Split beans were counted and massed to determine the percentage split in canned beans. After this procedure, the canned beans were dried in an oven (Blue-M/Lindberg MO1430A-1 Mechanical Convection Oven) at 130°C for 1 hour
(Agrawal, 2004) and ground in a standard coffee grinder to produce a flour that was used in the analysis of antinutritional factors (phytic acid and tannins).
Phytic Acid Content
Phytic acid content of raw, treated and untreated canned beans was determined by the method outlined by Wheeler and Ferrel (1971). Two g of flour sample was extracted with 50 mL
3% trichloroacetic acid (TCA) with mechanical shaking (VWR DS 500 orbital shaker) for 45 minutes with occasional swirling by hand. The slurry obtained was centrifuged (Beckman Coulter
Allegra 6KR centrifuge) and 10 mL aliquot of the supernatant was transferred into a 40 mL conical centrifuge tube. Four mL FeCl3 solution was added to the aliquot and heated in a boiling water bath for 45 minutes. One or two drops of 3% sodium sulfate in 3% TCA were added and further heated until the supernatant was not clear. Then the solution was centrifuged and carefully decanted as a clear supernatant.
The precipitate was washed twice by dispersing in 20 to 25 mL 3% TCA followed by heating in boiling water bath for 5 to 10 minutes and then was centrifuged. Again the wash was 37 repeated by using distilled water. The precipitate was then dispersed in few ml of water and added with 3 mL 1.5 N NaOH with mixing. The volume was made up to 30 mL with distilled water and heated in boiling water bath for another 30 min. Then the precipitated solution was quantitatively filtered hot through Whatman No. 2. The precipitate from the paper was again dissolved with the help of 40 mL hot 3.2 N HNO3 into a100 mL volumetric flask. The paper was washed with several portions of distilled water, collecting the washings into the same flask. The cooled flask was diluted to volume of 100 mL with distilled water. Five mL of aliquot was transferred to another 100 mL volumetric flask and diluted to approximately 70 mL. Another addition of 20 mL of 1.5 M KSCN (potassium thiocyanate) was made and diluted to volume and the color was read immediately within 1 min at 480 nm in spectrophotometer (Spectronic 20D+) available at
University of Wisconsin-Stout. Also the reagent blank was analyzed with each set of samples.
The iron content was determined from the previously prepared standard curve and the phytate phosphorus from the iron resulted assuming a 4:6 iron: phosphorus molecular ratio (Wheeler and
Ferrel, 1971).
Tannin Content
Quantitative estimation of tannins was carried out using the Vanillin assay method (Price et al., 1978). A 200 mg sample of bean flour was extracted using 10 mL 1% (v/v) concentrated
HCl in methanol for 20 min in capped rotating test tubes. Vanillin reagent (0.5%, 5 mL) was added to the extracts (1mL) and the HCl solution (4%, 5 mL) was also added to the second set of blank samples. The samples were left in the water bath for exactly 20 min, and were removed and the absorbance was read at 500 nm. A standard curve was prepared expressing the results as catechin equivalents, i.e. amount of catechin (mg mL-1) which gives a color intensity equivalent to 38 that given by tannins after correcting for blank. Then tannin content (%) was calculated according to the equation (Idris et al., 2006):
Catechin equivalent (CE) %
Where C, concentration obtained from the standard curve (mg mL-1).
Splitting of Beans
The extent of splitting in the canned beans was evaluated by separating beans from duplicate cans into two categories: (1) little or no split-beans with no longitudinal splits and with no transverse split longer than 1/5 of the small circumference of the beans; (2) significant split-all beans with greater splitting than for category 1. All beans were evaluated for splitting by the investigator. The % split was obtained as the mass of significant split beans to the mass of total bean samples (Loggerenberg, 2004).
Moisture Content of Beans
Moisture determination was based on ASABE standard procedure 2003. In this method 5 g of the soaked beans were weighted in aluminum drying discs and then placed in a mechanical oven (Lindberg/blue, mo 14505A-1, Asheville, NC) at 103°C for 72 h. After drying, the final weight was calculated and then moisture content was determined. The general formula for moisture content determination is given by the following equation 1.
WdWw Mc 100 Ww
Where: Mc = moisture content (%) of material, Ww = wet weight of the sample and Wd =weight of the sample after drying
39
Statistical Analysis
All work was conducted twice in triplicates and the data presented are means ±standard deviation on the dry weight basis. Duncan’s multiple range tests was used to determine significant differences (p < 0.05).
40
Chapter IV: Results and Discussion
This chapter includes a discussion on the results obtained and compares the findings to those of other researchers. This chapter concludes with the interpretation of data obtained.
The dark red kidney beans were tempered in an environmental chamber (EC) at 45°C and
95% R.H. for 12 h and 24 h, respectively. The tempered beans were then pretreated, which included soaking and blanching followed by canning. The canning process was carried out in a retort canner at 240°F for 40 minutes. The antinutrient content of canned beans was analyzed by determining phytic acid content of beans using Wheeler and Ferrel (1971) method, while the tannin content was determined by Vanillin-assay method (Price et al., 1978). The percentage split of canned beans was determined to evaluate the canning quality of canned beans. The reduction in antinutrients level in kidney beans was compared with the results obtained from various similar studies. Twelve different kinds of treatment conditions were selected to assess the reduction of antinutrients and to evaluate the quality of canned beans by the measurement of its splitting along with moisture content (MC), another key quality attribute in the canning process, which is discussed below.
Moisture Content of Beans after Tempering and Soaking
It has been found that the desired moisture content of beans before canning needs to be 53 to 57% (Hosfield & Uebersax, 1991). The objective of the determination of the moisture content of kidney beans was to estimate the time of tempering and soaking and to achieve the desired moisture content of 53-57% required for canning of beans. Three different tempering times of 6 h,
12 h and 24 h were studied (Thapa et al., 2009) and the aim was to achieve the moisture content between 53-57% in tempered and soaked beans.
The moisture content determination was based on the standard air-oven method (ASAE standards, 2003) and the computed results of the moisture contents are shown in Figure 4 that 41 indicates that tempering beans for 12 and 24 h reduces the time it takes to soak the red kidney beans. Tempering beans had noteworthy implications on their hydration; for example, 12 h tempering followed by subsequent soaking of 2 h increased the moisture content from
14.27±0.01% to 52.40±1.62%.
Figure 4. Effect of tempering (45°C/95% R.H.) at 6 h, 12 h and 24 h on moisture content of beans soaked for 0, 1, 2, 3, 4 and 5 h, respectively.
The beans tempered for 24 h were soaked for 0, 1, 2, 3, 4 and 5 h and it was noted that the moisture content varied after different soaking times from 1 to 5 h from 14.27±0.01% to as much as 60.88±2.65%. However, the desirable moisture content of 54.07% in kidney beans was found after soaking for 2 h which was determined based on the research findings of Hosfield &
Uebersax (1991).
It has been noted that too low of a MC (less than 11%) at the time of processing beans could lead to water imbibition problems during processing (Nordstrom & Sistrunk, 1979) as well as affecting the rate of water uptake (Hosfield & Uebersax, 1979). Another factor that can result in affecting water uptake is that if beans become too dry (M.C < 11%) before soaking they will 42 become water-impermeable. Too low initial MC (less than 11%) of beans lead to brittle seed coats with consequential cracking, thereby delivering a poor quality canned product (Nordstrom
& Sistrunk, 1979). Dry beans (11 – 14 % moisture content) therefore will split more during canning than semi-dry beans (50 – 60 % moisture content) (Gonzalez et al., 1982).
The tempering process of beans in high humidity conditions of 95% R.H. with 45°C decomposes the pectin substances, weakens the cell connections and decreases the shearing strength. Current results showed that tempering red kidney beans in a high humidity environment reduced the soaking times with the attainment of the desired moisture content (53-57%). This was possible because of the vapor pressure difference between the humid environment conditions
(high vapor pressure) and dry bean seed (low vapor pressure,) which caused the formation of a capillary pore as the water vapor migrated into the bean matrix and hence altered the microstructure (Thapa et al., 2009). The desired M.C (53-57%) was achieved from 12 h and 24 h tempering and 2h soaking. This tempering process also helped to reduce antinutrients such as phytic acid and tannins which are discussed below.
Phytic Acid Content of Canned Beans
Phytic acid (PA) in legumes is one of the major concerns in bean consumption.
Dry beans are widely known for their fiber, mineral and protein contents. Thus, they are important components of a healthy diet. On the other hand, phytic acid in the beans chelates mineral cations and interacts with proteins forming insoluble complexes that lead to reduced bio- availability of minerals and reduced digestibility of protein (Reyden & Selvendran, 1993).
Phytates have also been implicated in decreasing protein digestibility by forming complexes and also by interacting with enzymes such as trypsin and pepsin (Reddy & Pierson, 1994). 43
Table 2 summarizes the phytic acid content of raw and canned dark red kidney beans with various treatment conditions. The PA concentration in the raw dark red kidney bean was found to be 23.94 mg/g and this value was comparable with those of a previous report (Abd El-Hady &
Habiba, 2003). A reduction in phytic acid content was observed that depended upon the treatment conditions. For example, in the current study, the phytic acid reduction was found to be significant (p<0.05) for both 12 h and 24 h tempering as compared to raw dry kidney beans as shown in table 2.
Reduction in phytic acid was determined to be 84% as a result of the 24 h tempering- soaking-blanching-canning method; however, this method offers a long processing time. A shorter processing time, 12 h tempering-soaking-blanching-canning, allowed for about 62% reduction in phytate. Approximately more than half of the phytic acid was lost in kidney beans by the combined effect of the tempering, soaking, blanching and canning process. Phytic acid was not significantly different between 24 h tempering-canning method and 12 h tempering- blanching-canning method but in both processes there was a significant reduction of 45-46% of phytic acid when compared to the raw kidney beans as shown in table 2. The reduction by the blanching and canning processes was most likely due to hydrolysis of phytic acid as discussed in other studies (Khatoon & Prakash, 2004; Rehman & Shah, 2005). Also there was no significant difference between 24 h tempering-blanching-canning and 12 h tempering-soaking-blanching- canning method. Higher reduction of phytic acid was noted in 12 h tempering-soaking-blanching- canning method; therefore, it seems that the cumulative effect of tempering, soaking, blanching and canning helped to reduce the levels of phytic acid. Different values in the phytic acid reduction of several legumes attributed to the cooking methods such as cooking at 100°C for 10,
20 and 30 min, and autoclaving at 121°C for 15 min were previously reported (Vijayakumari et 44 al., 1998). When noting the 24 h tempering-soaking-blanching-canning process, it was found that a significant reduction (84%) (p<0.05) of phytic acid in dark red kidney beans resulted. However, this process requires a long treatment time which might be the greater disadvantages to the canning company compared to a commercial soaking process. Therefore, the optimal treatment condition would be the 12 h tempering-soaking-blanching-canning process, which significantly reduced the level of phytic acid and processing time over the commercial 20 h soaking-canning process.
45
Table 2
Effect of various treatments on the phytic acid content of dark red kidney beans and subsequent reduction (%) in dark red kidney beans
Treatment1 Phytic Acid Content2 Reduction (%)
(mg/g)
Raw 23.94±0.35 A
20S+C (Commercial) 13.50±0.35 E 44
12T 21.22±0.12 B 11
12T+C 17.05±0.23 D 29
12T+B+C 13.02±0.12 F 46
12T+S+C 11.45±0.00 G 52
12T+S+B+C 9.19±0.20 H 62
24T 19.30±0.11 C 19
24T+C 13.08±0.00 F 45
24T+B+C 9.27±0.11 H 61
24T+S+C 6.94±0.00 I 71
24T+S+B+C 3.80±0.12 J 84
1 Represents treatment combinations where T= Tempering, B= Blanching, S= Soaking and C=
Canning and 12, 20 and 24 indicates the treatment time in hour.
2 Values are means of three determinations ± standard deviation; values of each column followed by different letters are significantly different (p<0.05). 46
Table 2 showed that tempering help to reduce the level of phytic acid content in comparison to commercial canning process. The tempering process that offers the temperature of
45°C inside the EC for 12 h and 24 h reduced the phytic acid by thermal activity. Thermal degradation of these molecules as well as changes in their chemical reactivity or the formation of insoluble complexes, could explain the significant reduction of antinutrients by thermal processing (Barroga, Laurena & Mendoza, 1985; Kataria Chauhan & Punia, 1989). In the current study, the decrease in phytic acid during tempering might be due to the moisture obtained from high humidity environment that is postulated to weaken the cellular connection in beans and this resulted in increased porosity, which may have aided in the loss of the phytic acid.
A significant reduction (p<0.05) of 44% for phytic acid (13.5 mg/g) was obtained on commercial 20 h soaking-canning method compared to raw kidney beans (23.94 mg/g). It was reported that soaking lowered the phytic acid content, and the extent of reduction increased with an increased soaking period. This reduction may be attributed to leaching out of phytate ions into the soaking water, and the losses of the phytate ions may be due to the increased permeability of seed coat (Duhan et al., 1989). This decrease in phytate could be attributed to the hydrolization by phytases during soaking, and to the formation of insoluble complexes between phytate and other compounds of dry beans (Kataria et al., 1988; Lestienne et al., 2005). Phytic acid reduction was reported as 28% in black gram bean after being soaked for 12 h by Kataria et al. (1988). A significant decrease was previously reported in phytic acid for soaked-cooked beans and the greatest reduction was noted as 47.18% compared with raw beans (Barampama & Simard, 1994).
Additionally, Lestienne et al. (2005) reported that the reduction of the phytic acid content varied from 17 to 28% in different cereals and legumes after being soaked for 24 h at 30°C. 47
It has been reported that cooking beans, particularly after soaking them, will reduce the phytic acid in Phaseolus vulgaris L. (Iyer et al., 1980). However, Akindahunsi (2004) concluded that the phytic acid contents increased by the soaking and cooking processing of African oil beans. Vidal-Valverde et al. (1998) observed that soaking fava beans in either water, acid, or base solutions did not produce significant changes (p<0.05) in phytic acid levels. Boiling of legumes also did not result in a significant breakdown of their phytic acid content (Kumar et al., 1978).
Ologhobo and Fetuga (1984) also could not record a significant reduction in phytic acid of soybeans due to cooking, autoclaving, and soaking. Microwave heating of soybeans caused a 23% phytic acid reduction after 9 min and 46% after 15 min, while gamma irradiation (1 kGy) reduced the phytic acid content of soybean by only 4% (Hafiz et al., 1989).
In contrast, reductions in phytic acid contents of cereals and legume seeds with sprouting have been frequently reported (Ibrahim et al., 2002). These reductions are mainly due to an increase in the phytase activity, leading to a solubilization of phytates once the beans have sprouted (Camacho et al., 1992). The simple and inexpensive technique of sprouting has been therefore recommended for both in home and industrial use. In the current study, tempering for 24 hours is comparable to the effectiveness of sprouting for the reduction of phytic acid and other antinutrients. Previous research conducted in red kidney beans by Yasmin et al. (2008) found that
43% of phytic acid was reduced by sprouting for 96 h. Likewise 19% of reduction of phytic acid was noticed in the current study by a tempering process of 24 h. In earlier studies, sprouting has also been reported to have a diminishing effect on the phytic acid content of various legumes like the moth bean (Khokhar, 1984), rice bean and fava beans (Saharan, 1994) and the pigeon pea
(Duhan et al., 2002). Additionally, Duhan et al. (2002) reported that the cumulative effect of soaking, cooking and dehulling were more pronounced than soaking alone for lowering the phytic 48 acid content in pigeon pea. Similarly, it can be seen in the current study that the combined effect of tempering, soaking, blanching and canning was very effective in the reduction of phytic acid.
Tannin Content of Canned Beans
Generally, tannins found in beans may form insoluble complexes with proteins thus decreasing the digestibility of proteins (Uzoechina, 2007). Tannins may decrease protein quality by decreasing digestibility and palatability, damaging the intestinal tract, and enhancing carcinogenesis (Makkar & Becker, 1996). Furthermore, tannins could impair iron availability
(Svanberg et al., 1993; Udayasakhara-Rao, 1995).
Table 3 shows results for tannin content of dark red kidney beans as a function of processing and it is noted that compared to raw beans, a significant (p<0.05) reduction in tannin levels was observed after 12 h tempering, 24 h tempering and other treatments. There were more than 50% and 29% reduction of tannin content in 24 h and 12 h tempering, respectively. Since tempering is a type of thermal processing method, the decrease in tannin content could be related to the fact that these compounds are heat labile (Rakic et al., 2007) and degrade upon heat treatment. Also the moisture obtained from high humidity environment may have increased the porosity of beans by the vapor pressure difference in the cell connection. Therefore, the exposure of moist beans to high temperature in the environmental chamber might have allowed for degradation of the tannin content.
There was no significant difference between 20 h soaking-canning method and 12 h tempering-blanching-canning method. Treatment of 12 h tempering-soaking-canning caused a
75% reduction in tannin content. The greatest reduction in tannin content by 95% compared to raw beans was caused by 24 h tempering-soaking-blanching-canning method. There was no significant difference between three different treatments: 24 h tempering-blanching-canning 49 method, 12 h tempering-soaking-blanching-canning method and 24 h tempering-soaking-canning method. The reduction of tannins after tempering, soaking, blanching and canning is mainly due to the fact that those compounds are water soluble (Kumar, Reddy & Rao, 1979) and consequently leach into the liquid medium (Vijayakumari, Pugalenthi & Vadivel, 2007). In the current study, the commercial 20 h soaking-canning method also significantly reduced the tannin content by 63% when compared to the raw dark red kidney beans. These losses may have originated from the diffusion of the tannins into the water during soaking, and canning, as well as possible binding of tannins with proteins and other organic substances during blanching (Reddy et al., 1985; Barampama & Simard, 1994).
50
Table 3
Effect of various treatments on the tannin content (mg/g) and subsequent reduction (%) in dark red kidney beans
Treatment 1 Tannin Content 2 (mg/g) Reduction (%)
Raw 21.6±0.99 A
20S+C (Commercial) 8.00±0.99 F 63
12T 15.3±0.12 B 29
12T+C 13.21±0.78 C 39
12T+B+C 7.28±0.45 F 66
12T+S+C 5.40±0.99 G 75
12T+S+B+C 3.96±0.33 H 82
24T 10.6±0.37 D 51
24T+C 9.16±0.75 E 58
24T+B+C 4.23±0.67 H 80
24T+S+C 3.74±0.33 H 83
24T+S+B+C 1.08±0.43 I 95
1 Represents treatment combinations where T= Tempering, B= Blanching, S= Soaking and C=
Canning and 12, 20 and 24 indicates the treatment time in hour.
2 Values are means of three determinations ± standard deviation; values of each column followed by different letters are significantly different (p<0.05).
It can be seen that greater reduction of 82% in shorter processing time was observed in 12 h tempering-soaking-blanching-canning method. Important reductions of 33.1-45.7% in the 51 tannin content of dry beans were also reported in an earlier study, when different cooking methods such as ordinary cooking at 100°C for 10 min and autoclaving at 121°C for 10, 20, 40,
60 and 90 min were applied (Rehman & Shah, 2005). Similarly the thermal processing condition of 115°C for 40 min in an autoclave used in the current study also allowed a reduction of tannins.
The tannin content was found to be significantly reduced (<0.05) in all processes that were thermally processed in an autoclave (canning) (Table 3). These results are consistent with the findings of other studies in which complete elimination of tannins on cooking fava beans
(Sharma & Sehgal, 1992) were observed while autoclaving at 121°C for 25 min. The reduction in tannins in cooked seeds had been recorded by earlier investigations on plant foodstuff (Habiba,
2000; Nithya, Ramachandramurty & Krishnamoorthy, 2007). The reductions noted may be due to the loss of compounds at high temperatures or to degradation or to interaction with other seed components, such as proteins, to form insoluble complexes. Shimelis and Rakshit (2007) found that both soaking and cooking/autoclaving caused a significant reduction of 75% of tannin contents of kidney beans and the combined effect was significantly greater than cooking or soaking alone. The combinations of soaking and cooking/autoclaving were able to eliminate/reduce heat-stable and heat-sensitive antinutrients (Shimelis & Rakshit, 2007). These results compare with the current study’s results in that the combination of 12 h tempering- soaking-blanching-autoclaving significantly reduced (p<0.05) by 82% the tannin content of beans.
Splitting of Dark Red Kidney Beans
The effect of various processing methods on the percentage splits of dark red kidney beans is presented in Figure 5. Among the various processing methods used, the commercial soaking process had the greatest splits of 20.57%, while those tempered for 12 and 24 h and then canned had only between 2-6% splitting. Therefore it can be inferred that the splitting would result from 52 over-water uptake level in beans during soaking and to some extent due to the thermal processing in retort canning and/or tempering. It may be speculated that a cause of transverse splitting was the swelling of the bean during cooking producing stress on the skin and/or the weakening of the skin during cooking so that this stress resulted in loosened skin. It was reported previously that beans that have more mass, due to greater water uptake levels, have a greater tendency to split
(Forney et al., 1990). The beans, which were soaked for a longer time and thermally processed, had greater percentages of splitting. The reason for this could be related to the excessive time allowing for swelling of the beans that placed the skin under pressure, causing it to rupture.
Another reason for the splitting would be the amount of CaCl2 used in the canning medium. In the current study the use of CaCl2 might have decreased the drain weight and increased the firmness of beans. This was similar to the study of Uebersax, (1985) in which it was found that the increased calcium in the soak water or the brine depressed final drained mass and moisture content and increased firmness of pinto and navy beans. Similarly, Van Buren et al. (1986) found that the firmer beans and less drain weight beans would have fewer splits. The observation showed that lower percentage of split was associated with lower drained weight and greater firmness that agrees with those values presented by Davis (1976) and Junek et al. (1980). Size of beans also matters in the overall splitting of beans. Size depends on the different types of dry bean varieties with larger sized having a value of 48.77 g/100 beans would take up less water during canning, due to a larger volume-to-surface ratio, with consequential lower split values (Faris &
Smith, 1964).
53
Figure 5. Percentage split in canned beans with various treatment conditions
1 Represents treatment combinations where T= Tempering, B= Blanching, S= Soaking and C=
Canning and 12, 20 and 24 indicates the treatment time in hour.
2 Values are means of three determinations ± standard deviation; values of each column followed by different letters are significantly different (p<0.05).
A 12 h tempering-soaking-canning method and 12 h tempering-soaking-blanching- canning had the splitting of about 7.86% and 11.00%, respectively. There was no significant difference between the percentage splitting of 24 h tempering method, 24 h tempering-soaking- blanching-canning method, 12 h tempering-canning method and 12 tempering-blanching-canning methods. The tempered beans are firmer and have a lower chance of splitting compared to commercially soaked beans. The greater percentage of splitting (12.54%) was observed in 24 h tempering-soaking-canning process. The beans processed for a longer time with various treatment 54 steps before canning could lead to a breakdown of seed coats resulting in the splits seen during canning. Also excessive bean breakage during cooking would result in starch exudation into the canning medium, with consequential clumping of individual beans. Softening of beans while processing is thus important, but beans must still maintain their individual integrity (Hosfield &
Uebersax, 1980).
Figure 6 shows the color difference in commercial canned beans compared with the tempered canned beans. The discoloration in commercial canned beans was due to the 20 h soaking in water and thermal processing. The long soaking time and the migration of brine into the beans caused the discoloration in commercial canned beans. Similarly the greater percentage of spitting was noticed in commercial canned beans as apparent in Figure 6. The tempered canned beans appeared firmer and darker in color. The long tempering process caused the beans to become darker in color. The beans obtained from tempering and canning process have less split but the overall appearance was altered.
Figure 6: Canned beans obtained from commercial soaking and canning process (left)and canned beans obtained from tempering and canning process (right) 55
Figure 7: Example of split beans after thermal processing due to high water uptake levels
Figure 7 shows that the splitting of kidney beans often occurs after the commercial canning process. This kind of splitting is due to high water uptake and excessive swelling. The high temperature and pressure treatment during the thermal processing also caused the breakdown of seeds. Again, over-processing could have caused splits or high water uptake levels (Forney et al., 1990). The amount of CaCl2 used in the canning medium, type of canning medium, type of legume seeds, type of soaking solution, and effect of treatment condition all several factors reported to be responsible in the final quality of canned beans.
Hence, from the current study, the ideal treatment condition for optimum canning quality of beans would be 12 h tempering-canning processes, however; the most effective method for antinutrient reduction and desired canning quality would be based on 12 h tempering-soaking- blanching-canning method.
56
Chapter V: Conclusion
The purpose of this study was to evaluate the effect of tempering process on antinutrients level by analyzing the phytic acid and tannins and thereby examining the quality of canned dark red kidney beans. Beans were obtained from Chippewa Valley Bean Company Inc. (Menomonie,
WI). The bean samples were tempered, soaked, blanched and thermally processed according to the study design and prepared for further chemical analysis and quality evaluation. The samples were analyzed using a spectrophotometry technique for antinutrients and quality was judged based on percentage splits. Data obtained were compared with the standard curve of individual components to quantify antinutrients.
The tempering process was successfully used in the optimization of canning process of dark red kidney beans. The times of 12 and 24 h tempering with a 2 h soaking time were studied and incorporated in the canning process to shorten the long soaking process of 20 h and to improve the nutritional and overall quality of canned beans. Out of twelve different treatment conditions used in canning process of beans, the 12 h tempering-soaking-blanching-canning process was found to be very effective for the greatest reduction of phytic acid (62%). While, 24 h tempering-soaking-blanching-canning process was found to be the most advantageous in reducing the phytic acid content by as much as 84%. This process was found to be very efficient as compared to a commercial soaking process used in typical canning companies.
This study showed that the tannin content in dark red kidney beans reduced significantly with the treatment process of 12 h tempering-soaking-blanching-canning by 82%. This would be the shortest treatment process that reduced a large percentage of antinutrients. On the other hand, the tannin content reduction was found to be reduced by 95% in 24 h tempering-soaking- 57 blanching-canning process. However, this process has a disadvantage of having a longer canning cycle.
This study also demonstrated that the percentage split in tempered canned beans being lowered more than with the commercial soaking process. The percentage split in 12 h tempering- canning process and 24 h tempering-canning process was found to be 2-3%. However, the process of 12 h tempering-soaking-blanching-canning, which was found to be very efficient process for the reduction of antinutrients discussed earlier, had a splitting value of 11%. Hence the overall nutritional and quality benefits can be achieved in the 12 h tempering-soaking-blanching-canning process.
The research of this finding showed that the application of tempering in the canning process can drastically reduce the antinutritional load of dark red kidney beans with the incorporation of soaking and blanching. Therefore, since kidney beans are proposed as ingredients in the human diet, any of these conducted treatments are strongly advocated to be applied in processing prior to their consumption to ensure their safety and quality based on phytic acid, tannin content, and splitting.
Recommendations
1. Investigate the effect of tempering on the antinutritional levels of other legumes and dry
beans.
2. Investigate the effect of tempering on different types of antinutrients in legumes, cereals,
dry beans and other plant foods.
3. The quality and sensory evaluation of canned beans obtained from the tempering and
canning process can be done. 58
4. Investigate the exact tempering time and soaking time for the optimization of canning
process.
5. Analyze the antinutritional factors of kidney beans with the help of some other
sophisticated instruments like HPLC, GC/MS etc.
6. Investigate the physical, chemical and microbiological parameters of canned beans
prepared from the tempering process.
7. Microbiology study of the soaked water of beans before canning process.
59
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