APTEFF, 45, 1-283 (2014) UDC: 637.1/.3:[66-97:636.085-7 DOI: 10.2298/APT1445055M BIBLID: 1450-7188 (2014) 45, 55-66 Original scientific paper

STORAGE TEMPERATURE: A FACTOR OF SHELF LIFE OF PRODUCTS

Nurgin R. Memiši1, Slavica M. Vesković Moračanin2, Marija M. Škrinjar3, Mirela D. Iličić3, Mira Đ. Ač3

1 AD Mlekara – , Tolminska 10, 24000 Subotica, 2 Institute for Meat Hygiene and Technology, Kaćanskog 13, 11000 , Serbia, 3 University of Novi Sad, Faculty of Technology Novi Sad, Bulevar cara Lazara 1, 21000 Novi Sad, Serbia,

An experiment was designed to monitor the durability of certain dairy products stored at proper temperatures (8oC) and elevated temperatures (14oC) within their shelf life. Samples of fermented products were tested during 25 days, samples of spread products over 80 days, while soft white cheese samples were analyzed during a storage period of 100 days. In the defined study periods, depending on the type of product, pH and aw value of the product, as well as sensory analysis (odor, taste, color and consis- tency), along with microbiological safety, were investigated. The investigations were performed in accordance with national legislation. The results indicate that the products stored at 14oC showed significant acidity (lower pH value), changed sensory properties, and had an increased number of aerobic bacteria.

KEY WORDS: milk products, shelf life, storage temperature, quality

INTRODUCTION

It is well known that, depending of numerous internal and external factors, the growth of microorganisms during the storage of dairy products results in their sensory changes, i.e. spoilage. This is due to the fact that under the inadequate storage conditions, nutrients in the milk products are a good medium for the growth and development of individual groups of microorganisms. The diverse range of dairy products found on the market to- day is a result of the knowledge and experience acquired over the years. However, the contemporary consumer sets high requirements for the producer, expecting from it to stay abreast of modern trends, related to both high quality and product safety. In other words, the consumer’s primary requirement is that during the estimated time of storage the food remains safe, i.e. without adverse changes (1). The length of shelf life of milk products is primarily influenced by the number and type of microorganisms pre- sent in the as the primary raw material, state of packaging material, hygienic and sanitary conditions during the production cycle (washing and disinfection of the

* Corresponding author: Nurgin R. Memiši, AD Mlekara – Subotica, Tolminska 10, 24000 Subotica, Serbia, e-mail: [email protected] 55 APTEFF, 45, 1-283 (2014) UDC: 637.1/.3:[66-97:636.085-7 DOI: 10.2298/APT1445055M BIBLID: 1450-7188 (2014) 45, 55-66 Original scientific paper equipment, temperature regimes), as well as by the storage temperature of the final product. In most cases, the microorganisms that cause the spoiling of milk and dairy products (2,3) reduce to some extent their quality, which results in significant economic losses. The reduced quality results from different chemical and biochemical bonds which cause change of appearance, smell, texture, taste, and aroma of the products. The appearance of those bonds is conditioned by metabolic degradation of some components of the product, by microorganisms causing the spoilage or by their enzymes (4). is known as a good nutritive medium, with a relatively low pH, favorable for the development of acidophilic microorganisms, as opposed to cheese which is less acidic and contains less water, as well as added salts, resulting in low aw value, thus partially li- miting the growth and multiplication of certain microorganisms. In addition, with its firm consistency, cheese limits in some way the mobility of the microorganisms that cause spoilage (5). Fresh are unripened cheeses, which are manufactured by the coagulation of milk, or whey using acid, a combination of acid and rennet or a combination of acid and heat. Many processing factors (milk pre-heat treatment, rate and temperature of acidification, level of gel-forming protein, pH) influence the coagulum structure and hence the rheological and physico-chemical stability and nutritive value of the fresh cheese (6,7). Starter culture plays an important role in the process of coagulation and governs the flavor, body and texture of the cheese, and helps to suppress the growth of pathogenic and spoilage bacteria (8,9). During the past 30 years, the use of ultrafiltered (UF) milk for cheese making has attracted considerable attention throughout the world (8). Cheeses being successfully made from cow’s milk by the UF process, on an industrial scale, include Camambert, Feta and Mozzarela cheeses, as well as many varieties of soft cheeses from cow’s milk (Cottage cheese, Quarg cheese, Cream cheese, Domiati cheese, etc.). Generally, the ad- vantages of the cheeses made by UF process are higher pH, increased cheese yields, hig- her protein, fat and total solids content (8). The investigated fresh soft white cheese (Domiaty type) made from goat milk using UF process showed 85% reduction in total process time, as well as salt, starter culture, rennet and calcium chloride. The aim of this study was to investigate the effect of the storage temperature on the microbiological characteristics (lactobacilli, number of aerobic bacteria, CFU/g), physi- cochemical characteristics (pH value, aw), and sensory properties of the fermented milk products, cheese spreads and soft white cheese during their storage.

EXPERIMENTAL

The experiment was designed to monitor the durability of certain dairy products (fermented milk products, cheese spreads, and soft white cheese) stored at proper tempe- ratures (8oC) and elevated temperatures (14oC), within their shelf life. Samples were taken from each group of products, in original packaging units, immediately after pro- duction, and kept at predefined temperatures in the refrigerated chambers with automatic temperature control (8 and 14oC). Microbiological, physico-chemical and sensory inves-

56 APTEFF, 45, 1-283 (2014) UDC: 637.1/.3:[66-97:636.085-7 DOI: 10.2298/APT1445055M BIBLID: 1450-7188 (2014) 45, 55-66 Original scientific paper tigations were performed according to a plan which included testing of the finished pro- ducts immediately after manufacture, testing midway through the declared shelf life, and at the end of the shelf life.

Milk products and technological production procedure Fermented milk products

Raw milk standardized to 2.8% milk fat, was pasteurized and homogenized (95oC, 6 sec., P=150 bar). After cooling to the optimal temperature (38oC), homogenized milk was inoculated with yogurt culture -Bulk Set 442 – contains Lactobacillus delbruecki subsp. bulgaricus and Streptococcus thermophilus, (Danisco-Denmark). The fermentation pro- cess was considered completed when the fermented milk product has achieved a specific pH (4.65), then cooled (to 20oC), and the finished product was filled and packaged into PET packaging in a closed manufacturing system with hepa filters and adequate over- pressure.

Cheese spreads

Cheese spreads are products obtained from fermented cream. The cream containing approximately 21% milk fat was mixed with skimmed milk powder. After the heat treat- ment (105oC) and cooling to the optimal temperature (37oC), it was inoculated with a bu- tyric culture - Proba 505 - contains Lactococcus lactis subsp. lactis, Lc. lactis subsp. cremoris, Lc. lactis subsp. lactis biovar. diacetylactis, Leuconostoc mesenteroides subsp. Cremoris, (Danisco-Denmark). The fermentation process was interrupted by cooling, when the optimal pH (4.6) for the product was achieved, The formed byproduct was mixed with and stabilizer according to the manufacturer’s specification, and then heat treated in a thermizer to the optimal temperature (78-82oC). The hot product was fil- led into plastic containers and hermetically sealed with Al lids.

Soft white cheese, 45% milk fat in dry matter

Soft white cheese is a product obtained from pasteurized cow milk standardized to 3.75% milk fat. After ultrafiltration, the obtained retentate was pasteurized at a tempera- ture above 78oC, cooled in a system of coolers, and then transferred to a duplicator, where it was stored. The cheese culture - FRC 75- contains Lactococcus lactis subsp. cre- moris, Lactococcus lactis subsp. lactis, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus, (Danisco-Denmark). and commercial rennet were then si- multaneously added to the semi-finished product. In a closed industrial packaging system with inbuilt hepa filters, the product was filled into plastic containers of various volumes (250 g, 500 g and 1 kg), and then transported to the fermentation chamber. After the fer- mentation time of 20 min, a semipermeable membrane was placed on the surface of the product, over which a required quantity of salt (2%) was added, according to the manu- facturer’s specification. After this, the container was closed with an Al lid, and hermetic sealing was secured by thermal sealing, after which another protective lid was placed on the top. Then, the

57 APTEFF, 45, 1-283 (2014) UDC: 637.1/.3:[66-97:636.085-7 DOI: 10.2298/APT1445055M BIBLID: 1450-7188 (2014) 45, 55-66 Original scientific paper closed product was placed on a plastic palette and transferred to a chamber for additional (final) fermentation (10 h, 30-32oC), until the desired consistency and final pH (4.85) were achieved. After the completion of the fermentation, the product was intensively cooled in the cooler to a temperature of up to 8oC.

Microbiological analysis

Microbiological examination of the dairy products was performed in accordance with the Regulations of General and Special Conditions of Food Hygiene at any Stage of Pro- duction, Processing and Trade (10), according to the Regulation (EC) No 2073/2005 (11), as well as with the elements of self-control prescribed in the HACCP plans. Briefly, 25 g of each sample were transferred to a sterile stomacher bag and 225 mL of saline-peptone water was added and mixed for 30 seconds in the stomacher. Further decimal dilutions with the same diluents were made, and the following analyses were performed on dupli- cate agar plates: total viable count of microorganisms on Plate Count Agar (ISO 4833/2003) (12); mesophilic lactic acid bacteria (LAB) on a double layered MRS agar and incubated at 30oC for 48 h (ISO 15214/1998) (13); Escherichia coli on Violet Red Bile (VRB) agar (ISO 16649-1/2009) (14); Staphylococcus aureus on Baird Parker medi- um with added egg yolk tellurite emulsion (ISO 6888-1/1999) (15); yeast and moulds on Sabouraud-4% Maltose agar containing 2% of chloramphenicol. The dishes were incuba- ted at 25oC during 5 days (16). The detection and enumeration of Listeria monocytogenes and Salmonella spp were carried out following the procedure ISO 11290-1, 2/2004 and ISO 6579/2002, respectively (17, 18).

Physico-chemical analysis

The physico-chemical investigation included the determination of the pH values (pH meter, MA-5730, No 35 398 PAT, Iskra) and water activity (aw), using a hygrometer (Wert-Messer, Durotherm), at a constant temperature of 25ºC.

Sensory analysis

The sensory investigations were performed at three stages of production: finished pro- duct immediately after manufacture, testing midway through the declared shelf life, and at the end of the shelf life. A group of six panelists was formed from the pool of trained panel members for eva- luating sensory characteristics. Sensory characteristics of odor, taste, color and consis- tency were evaluated according to hedonic scale 1 to 3 (3 - “exceptionally acceptable”, 2- “acceptable”, 1- “unacceptable”). The total sensory score for excellent milk products was set as 12.

Statistical analyses

Statistical analysis was used to study the influence of chemical composition and sen- sory evaluation by single-factor analysis of variance (ANOVA). The differences between

58 APTEFF, 45, 1-283 (2014) UDC: 637.1/.3:[66-97:636.085-7 DOI: 10.2298/APT1445055M BIBLID: 1450-7188 (2014) 45, 55-66 Original scientific paper individual means were tested. Significant differences were considered for P<0.05, P<0.01 and P<0.001. Calculations were performed using Statistics for Windows 5.1 Stat Soft (Stat Soft 1996) (19).

RESULTS AND DISCUSSION

The results of physico-chemical investigations of milk products during different sto- rage periods are presented in Table 1. It can be seen that the pH value decreased slightly with storage time at 8oC. On the other hand, the pH value decreased significantly (P< 0.01) with storage time at 14oC. The pH of fermented milk products after 13 days of sto- rage showed the lowest value 3.96±0.04 and after 25 days of storage it was 4.01±0.017. Cheese spread samples were analyzed for the pH and water activity. No significant (P<0.01) changes of the values of these parameters were recorded throughout the 80 days of storage period for the cheese spread samples at 8oC. On the other hand, a very little and non-significant decrease of the pH value and increased water activity value were recorded after 80 days of storage at 14oC.

Table 1. Results of the physico-chemical testing of the products during the storage

Storage Type of product Days of testing temperature Day 1 Day 13 Day 25 Fermented milk pH value (Ā ±SD) products 8oC 4.42±0.014 4.20±0.013 4.26±0.093 14oC 4.43±0.035 3.96±0.040 4.01±0.017 Days of testing Day 1 Day 40 Day 80 pH value (Ā ±SD) 8oC 4.68±0.023 4.65±0.010 4.66±0.014 Cheese spreads 14oC 4.71±0.021 4.61±0.013 4.52±0.007 aw value 8oC 0.962 0.968 0.966 14oC 0.964 0.966 0.973 Days of testing Day 1 Day 50 Day 100 pH value (Ā ±SD) Soft white cheese, 8oC 4.82±0.015 4.73±0.014 4.65±0.018 45% milk fat in 14oC 4.83±0.012 4.15±0.010 3.64±0.007 dry matter aw value 8oC 0.958 0.966 0.968 14oC 0.959 0.977 - Ā – average value; SD − standard deviation; n = 240

59 APTEFF, 45, 1-283 (2014) UDC: 637.1/.3:[66-97:636.085-7 DOI: 10.2298/APT1445055M BIBLID: 1450-7188 (2014) 45, 55-66 Original scientific paper For the soft white cheese, the pH value decreased gradually from 4.82±0.015 and af- ter 100 days of storage at 8oC, it was 4.65±0.018. It was also seen that during the first 50 days the pH value did not decrease significantly (P<0.05), but at the end of the storage period (100 days) this decrease was-significant (P<0.01). For the soft white cheese sam- o ples stored at 8 C, the aw value did not change (approximately 0.96) significantly, while for the same samples stored at a higher temperature, the aw value increased to 0.977 after 50 days of storage and at the end of shelf life it was not measured because the samples showed pronounced signs of spoilage (changed consistency, structure, and sensory pro- perties). The microbiological test results showed that all the tested dairy products samples did not contain L. monocytogenes, E. coli, Salmonella spp, Staphylococcus aureus, and/or yeasts and molds. The finished products, as well as all the stored dairy products were safe for consumption.

Table 2. Results of microbiological testing of the products during the storage

Storage Type of product Day of testing temperature Day 1 Day 13 Day 25 Fermented milk Total number of LAB, CFU/mL (Ā±SD) products 8°C 3.4×108 a 1.7×108 a 2.8×107 a 14°C 3.4×108 a 1.4×108 b 2.3×107 b Days of testing Day 1 Day 40 Day 80 Cheese spreads Total aerobic microbial count, CFU/g (Ā±SD) 8°C <10 a θ a θ a 14°C θ b 60 b 200b Days of testing Soft white cheese, Day 1 Day 50 Day 100 45% milk fat in Total aerobic microbial count , CFU/g (Ā±SD) dry matter 8°C θ θ a θ a 14°C θ 150b 6x 103 b CFU  colony forming units; LAB − lactic acid bacteria; detection limit 10 cfu/g Ā – average value; SD − standard deviation; n = 240 a,b Means within the same column with different superscripts differ significantly (p<0.05)

The population of lactobacilli in the fermented milk products was characteristic for this type of product. However, no significant changes in lactic acid bacteria count were observed throughout the storage period at both investigated temperatures (Table 2). The total aerobic microbial count was below detection limit throughout the storage period at 8oC for both spread cheese and soft white cheese. On the other hand, a gradual increase of the aerobic microbial count was observed at elevated temperature for both products. The aerobic microbial count in soft white cheese was 6.0×103 CFU/g after 100 days of storage at 14oC (P<0.05).

60 APTEFF, 45, 1-283 (2014) UDC: 637.1/.3:[66-97:636.085-7 DOI: 10.2298/APT1445055M BIBLID: 1450-7188 (2014) 45, 55-66 Original scientific paper Table 3. Results of sensory analysis of the milk products during the storage

Storage Day of testing Type of product temperature Day 1 Day 13 Day 25 Consistency 8°C 3.0±0,00NS 3.0±0.00b 2.93±0.25b (Ā±SD) 14°C 3.0±0,00 2.06±0.70a 1.66±0.61a Fermented ° Odor 8 C 3.0±0.00NS 2.86±0.35b 2.93±0.25b milk (Ā±SD) ° a a products 14 C 3.0±0.00 1.93±0.70 1.86±0.74 Taste 8°C 3.0±0.00NS 3.0±0.00b 2.86±0.35b (Ā±SD) 14°C 2.93±0.25 2.0±0.37a 1.73±0.59a Appearance 8°C 3.0±0.00NS 3.0±0.00b 3.0±0.00b

(Ā±SD) 14°C 3.0±0.00 2.2±0.67a 2.00±0.37a ° 8 C 12.0±0.00NS 11.86±0.07b 11.72±0.05b Total 14°C 11.93±0.035 8.19±0.11a 7.25±0.15a Day of testing

Day 1 Day 40 Day 80 Consistency 8°C 3.0±0,00NS 3.0±0.00b 2.83±0.41b (Ā±SD) 14°C 3.0±0,00 1.46±0.64a 1.26±0.45a Odor 8°C 3.0±0.00NS 3.0±0.00b 3.0±0.00b Cheese (Ā±SD) 14°C 3.0±0.00 1.66±0.62a 1.33±0.48a spreads Taste 8°C 3.0±0.00NS 2.93±0.25b 2.86±0.35b (Ā±SD) 14°C 3.0±0.00 1.4±0.50a 1.0±0.00a Appearance 8°C 3.0±0.00NS 3.0±0.00b 3.0±0.00b (Ā±SD) 14°C 3.0±0.00 1.86±0.74a 1.33±0.48a ° 8 C 12.0±0.00NS 11.93±0.035b 11.69±0.09b Total 14°C 12.0±0.00 6.38±0.20a 4.92±0.16a Day of testing

Day 1 Day 40 Day 80 Consistency 8°C 3.0±0,00NS 2.83±0.41b 2.8±0.56b (Ā±SD) 14°C 3.0±0,00 1.0±0.00a 1.0±0.00a Soft white Odor 8°C 3.0±0.00NS 3.0±0.00b 3.0±0.00b cheese, (Ā±SD) 14°C 3.0±0.00 1.0±0.0a 1.0±0.00a 45% milk 8°C NS b b fat in dry Taste 3.0±0.00 2.86±0.35 2.80±0.41 ° a a matter (Ā±SD) 14 C 3.0±0.00 1.0±0.0 1.0±0.00 Appearance 8°C 3.0±0.00NS 2.93±0.25b 2.73±0.45b (Ā±SD) 14°C 3.0±0.00 1.16±0.41a 1.0±0.00a 8°C NS b b Total 12.0±0.00 11.62±0.07 11.33±0.12 14°C 12.0±0.00 4.16±0.008a 4.0±0.00a Ā - average value; SD − standard deviation NS - no significant difference (p>0.05) a,b - Means within the same column with different superscripts differ significantly (p<0.05)

61 APTEFF, 45, 1-283 (2014) UDC: 637.1/.3:[66-97:636.085-7 DOI: 10.2298/APT1445055M BIBLID: 1450-7188 (2014) 45, 55-66 Original scientific paper On the day 1 of the postproduction, all investigated products (Table 3) had uniform sensory properties, characteristic for each type of product (P>0.05). At the storage tem- peratures of up to 14oC, the most pronounced changes were found for the soft white chee- ses, as well as cheese spreads. In the soft white cheeses, already midway through the shelf life (day 50) there were considerable changes (overall grade 4.16±0.008), of all sen- sory characteristics (onset of bitterness, changed structure, unpleasant odor), and the ob- served differences were statistically significant (P<0.05). The effect of various storage temperatures is directly linked to the lipolytic and proteolytic processes taking place in the product itself, with the intensity directly dependent on the external temperature. This is corroborated by the results of (20), stating that the intensity of proteolysis was more pronounced in the samples of Mozzarella cheese stored at higher temperatures (the expe- riment was done at 4 and 12oC). The mini cheeses stored at 18oC for 12 weeks had alte- red sensory properties compared to cheeses stored at 7oC for 24 weeks (21). In the inves- tigation of Kamleh et al. (22) it was found that the nominal shelf life of Halloumi cheese stored at 5oC was 79.6 days and dropped to 37.8 days at 15oC, suggesting the conformity of the quality changes in the product to the Q10 value of 2. However, the dramatic drop in the shelf life of the product stored at 25oC to 2.6 days was caused by detrimental chan- ges in the cheese appearance. In addition, the same regularity for the change of the sensory characteristics during the storage period was also noticed in the group of cheese spreads. Already midway through the shelf life (day 40), a rancid taste and changed structure appeared, with sta- tistically significant differences (P<0.05). In the fermented products stored at 14oC, a mild increase of the acidity, as well as of the intensity of syneresis were observed, with statistical differences between product samples stored at different temperatures at the P<0.05 level. Hruškar et al., (23) showed that during the storage of probiotic yogurt at the tempera- tures of 4 and 20oC there was a change of the quality of the stored products, and that the changes were more pronounced at higher storage temperatures. The decrease in the pro- duct quality was linked to the increase in the contents of lactic and citric acids. The inves- tigations of the microbiological processes in butter during the storage period and cooling temperatures (24) indicated that the increase of the total microorganism and lipolytic bacteria counts was intensive after the day 15, and that on the day 30 at 4oC the counts in- creased by up to 10 times. The same author stated that the change in the lipolytic bacteria count was directly proportionate to the increase in the total microorganism count. In a study of the effect of various storage temperatures (-12, 2, 8 and 12oC), as well as the presence of salt on the microbiological changes in five different types of thermo-pro- cessed products (25), it was stated that lower storage temperatures and the presence of salt had a significant effect on reducing the total number of microorganisms, coliform bacteria and yeasts, compared to their counts found in the products stored at higher tem- peratures. The UHT milk samples, taken in the spring and fall from five different distri- buted in different regions of France (north, north-west, south-west and central France), were stored at various temperatures (4, 20 and 40oC), and analyzed after 21, 42, 62, 90, 110 and 180 days, and it was established that higher temperatures (40oC) had a pronoun- ced effect on the pH decrease and increase in non-casein (26). The temperature of storage

62 APTEFF, 45, 1-283 (2014) UDC: 637.1/.3:[66-97:636.085-7 DOI: 10.2298/APT1445055M BIBLID: 1450-7188 (2014) 45, 55-66 Original scientific paper markedly influenced the time of gelation of UHT-sterilized milk. In general, gelation occurs more readily at room temperatures (20 to 25oC) than at low (4oC) and high (35 to 40oC) temperatures (27). Burdova et al. (28) have demonstrated that the storage temperature of 10oC reduces the shelf life of pasteurized milk to one third in comparison with the storage at 4oC. The average shelf life of the full cream pasteurized milk reached 31 days at 4oC, the average shelf life of skimmed pasteurized milk was 32.57 days. At 10oC, the average shelf life was 11 days for the whole and 10.71 days for skimmed pasteurized milk. The evaluation of proteolytic and lipolytic enzyme activities produced by psychrotrophic microorga- nisms at different storage temperature showed an increased activity of the psychrotrophic microorganisms after 2 - 3 d at 10oC. The storage at 4oC did not allow the production of comparable amounts of these enzymes for a three times longer interval.

CONCLUSIONS

Results of this research enable the following conclusions: The investigated dairy products: fermented milk products, cheese spreads, and soft white cheese, stored at 8oC showed no significant pH decrease, as opposed to the pro- o ducts stored at higher temperature (14 C). On the other hand, the established aw values for cheese spreads and UF cheeses showed no variation during the shelf life. The test results for sensory properties of the fermented milk products stored at 14oC demonstrated a ten- dency toward the increase in the acidity during the investigation period, and for the cheese spread samples a rancid taste was also established. For the cheese samples stored at 14oC, in the mid of storage period (day 50), a bitter taste, altered structure, as well as a certain unpleasant odor, were established, with a significantly reduced pH. The results for the microbiological status showed that during the shelf life, the investi- gated products were microbiologically adequate. No presence of pathogenic microorga- nisms was established. On the other hand, elevated storage temperatures caused an in- crease in the total bacteria count, mainly accompanied by a change of sensory properties, as well as by a decrease in the pH value.

Acknowledgement

The results presented in this paper are part of Project III, No 46009: “Improvement and development of hygienic and technological procedures in production of foodstuffs of animal origin with the aim of producing high-quality and safe products competitive on the global market” funded by the Ministry of Education, Science and Technological Development of the Republic of Serbia.

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TЕМПЕРАТУРА СКЛАДИШТЕЊА: ФАКТОР РОКА ТРАЈАЊА МЛЕЧНИХ ПРОИЗВОДА

Нургин Р. Мемиши1, Славица M. Весковић Морачанин2, Mарија М. Шкрињар3, Mирела Д. Иличић3 и Мира Ђ. Ач3

1 AД Млекара – Суботица, Tолминска 10, 24000 Суботица, Србија 2 Институт за хигијену и технологију меса, Качанског 13, 11000 Београд, Србија, 3 Универзитет у Новом Саду, Технолошки факултет, Булевар цара Лазара 1, 21000 Нови Сад, Србија.

У оквиру ових истраживања праћена је одрживост појединих група млечних производа, током њиховог рока трајања, складиштених како на адекватним темпе- ратурама чувања (8oC) такође, паралелно и на повишеним температурама скла-

65 APTEFF, 45, 1-283 (2014) UDC: 637.1/.3:[66-97:636.085-7 DOI: 10.2298/APT1445055M BIBLID: 1450-7188 (2014) 45, 55-66 Original scientific paper диштења (на 14oC). Након завршетка производње из сваке производне шарже про- извода код којих је праћена њихова одрживост, током рока трајања на различитим температурама чувања, узимани су узорци у оригиналним амбалажним паковањима који су смештени у расхладне уређаје са подешеним температурама чувања и скла- диштења (8 и 14oC). Узорци ферментисаних млечних производа су анализирани током 25 дана, сир- них намаза током 80 дана, док су узорци меких белих сирева анализирани током периода складиштења од 100 дана. Планом предвиђених контрола (почетак, сре- дина и истек рока трајања), у зависности од врсте производа, код узорака су вршена физичко-хемијска испитивања (pH вредност и aw воде код сирева), затим сензорна оцена (мирис, укус, боја и коензистенција) и микробиолошка контрола. Сва ис- питивања су урађена у складу са законском регулативом. На основу резултата ових испитивања констатовано је да је чувањем производа на неадекватним темпера- турама складиштења (14oC) дошло до повећања укупног броја аеробних бактерија, промене сензорних својстава производа као и смањења њихове pH вредности (повећања киселости).

Кључне речи: производи од млека, рок трајања, температуре чувања, квалитет

Received: 5 May 2014. Accepted: 8 September 2014.

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