CC BY
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Marek Sady, Jacek Domagala, Tadeusz Grega, Dorota Najgebauer-Lejko, Maria Walczycka, Dorota Kalicka ©
Department of Animal Product Technology, Food Technology Faculty, University of Agriculture in Krakow, Poland
EFFECT OF WHEY PROTEIN CONCRNTRATE ADDITION ON
PROPERTIES OF KEFIR PRODUCED FROM SKIMMED MILK
Abstract
The aim of the study was investigation of quality of fat-free, set-type kefir made at 11% (w/w) solid-non-fat level with addition of skim milk powder (SMP) and/or whey protein concentrate (WPC) blends. The ratio SMP/WPC in used blends was: 1/0; 1/1; 0/1. On 1st, 7th and 21st day of refrigerated storage kefir was analysed for sensory properties, titrable acidity, pH, free fatty acids (FFA), acetaldehyde, and diacethyl. Experimental kefirs were characterized by high sensory quality. The use of WPC slightly decreased sensory properties of kefirs. Fortification of milk for kefirs with skim milk powder and/or whey protein concentrate caused growth of titratable acidity with stable level of pH value as well. During storage time significant increase of acidity was stated. The storage time significantly decreased level of both analyzed volatile compound: diacethyl and acetaldehyde. Significantly higher level of this compound was characterized by kefir fortified with mixture of skim milk powder and whey protein concentrate. Increasing of contribution of WPC in milk for kefir caused the rise of FFA level in product. During storage period systematically growth concentration of FFA in all type of kefir.
Key words: kefir, whey protein concentrate, skim milk
Introduction
Kefir has been manufactured for hundreds of years in homes in the Caucasus Mountains. Microflora of kefir contains different species of lactic acid bacteria and yeasts. The production of kefir is unique in that it involves a mixed lactic acid/alcoholic fermentation of lactose. Although the major metabolite of fermentation is usually lactic acid, kefir can be defined as a self-carbonated milk beverage containing variable amounts of alcohol (Stepaniak and Fetlinski, 2003).
Cow's milk for the industrial production of kefir is usually not fortified. Kefir can be produced from full-fat, low-fat or skimmed milk.
During fermented milk production, the fortification of bulk milk with solids is used as it positively affects the sensory quality of final products. This process refers especially to non-fat fermented milk production. Skim milk is a raw material devoid of the component which is responsible for formation of positive sensory properties of dairy products.
The most popular way of milk fortification in milk solids is the addition of skim milk powder or other milk powders to liquid milk. Nowadays, due to milk
© Marek Sady, Jacek Domagala, Tadeusz Grega, Dorota Najgebauer-Lejko, Maria Walczycka, Dorota Kalicka, 2008
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fortification whey protein concentrate is often used besides skim milk powder. Whey protein ingredients are added to foods for nutritional and functional reasons. Whey proteins have a higher proportion of essential amino acids than casein and are judged to be the milk proteins with the highest value. Their biological value exceeds even that of whole egg protein (Sienkiewicz and Riedel, 1990). Each of whey protein fraction has been proven or implied to have unique functional, nutritional or nutraceutical properties. Some putative nutraceutical activities are digestive function (P-Lactoglobulin and glycomacropeptide), anticarcinogenic (a-Lactoalbumin), antimicrobal (lactoferin and lactoperoxidase) and passive immunity (immunoglobulins). It is known that a-lactoalbumin binds minerals (calcium, magnesium, zinc and cobalt) which are more readily delivered for adsorption in the human body (Foegeding and Luck, 2003).
The use of whey proteins in foodstuffs results not only in improved properties related to the physiology of nutrition in the final product, but also increases in particular utilization values. The protein preparations should not only stabilize disperse systems such as gels and foams, but also demonstrate good hydrophilic properties (solubility, water-binding and water retention capacity) as well as lipophilic properties (emulsion formation and stability, fat-binding and fat-retention capacity) (Sienkiewicz and Riedel, 1990). Practical employment of whey protein results from its positive influence on textural and rheological properties without of negative effect on taste and flavour.
Task, the aim of the article
The aim of the study was investigation of quality of fat-free, set-type yoghurt made at 11% (w/w) solid-non-fat level with addition of skim milk powder (SMP) and/or whey protein concentrate (WPC) blends.
Material and methods
For the preparation of kefir the bulk milk obtained from local farm was used. The experiment was performed during pasture feeding of cows. The starter culture Kefir DC for direct vat inoculation was supplied by Danisco (Denmark). Skim milk powder (SMP) obtained from the local market and whey protein concentrate (WPC) A235 (Lacma, Poland) were used to prepare formulations. Both products contain 34% protein and 95% of solid non fat.
For the kefir production whole milk was heated to 45 °C and centrifuged. Next, skim milk was standardized to content of 11% of solid non fat. The fortification process was carried out by adding blends of skim milk powder and whey protein concentrate. The ratio SMP/WPC in used blends was: 1/0; 1/1; 0/1. The kefir without supplementation (0/0) was a control group. Prepared kefir formulations were then heated to 65°C, twice homogenized at a pressure of 7 MPa. Afterwards the mixtures were pasteurised at 90°C for 10 minutes, cooled to incubation temperature and inoculated with starter culture in a quantity suggested by starter producer. After mixing of milk, the sterilized containers were filled and incubated at 21 °C until the mixtures gelled and pH reached 4.6. Then, prepared kefirs were cooled to 5°C and stored at this temperature until analysed. On 1st, 7th and 21st day of refrigerated storage the following determinations were carried out: pH (CP-215, Electron pH
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meter), titrable acidity (AOAC, 1995), free fatty acids (extraction-titrable Dole method by Deeth et al., 1976), diacethyl (spectrophotometry method by Pien, 1974) and acetaldehyde content (spectrofotometric method by Lees & Jago, 1965). The experiment was carried out in four independent replicates and obtained data was analysed statistically with the two-factor ANOVA and differences between means were assessed with the Duncan test.
Results and discussion Obtained results are presented in table 1-2. The data showed in table 1 present the parameters of analyzed kefir during 21 days of storage. The results of statistical analysis are presented in table 2.
The sensory characteristics of analyzed kefir ranged from 4,01 to 4,47 points. The best sensory quality revealed kefir fortified with SMP, it was similar to non fortified products - control group (0). The addition of mixture SMP/WPC or only WPC slightly decreased sensory properties of kefir. During the storage period all kinds of kefir decreased their sensory quality. Statistically significant differences were observed at 21st day of storage period (table 2). But during all storage time analyzed kefir got high score - over 4 points. Obtained results of sensory analysis showed that supplementation of milk by the whey protein concentrate positively influenced on consistency but decreased taste and flavour of kefir.
Similar results were done by Mleko (1996). He showed negative effect of WPC addition on sensory properties of yoghurts such as taste, but at the same time product with whey protein got higher score for consistency. According to Szczepaniak and Gorecka (2002) the consistency is the most important trait which is affected overall sensory characteristics. They proved that consumers prefer products with adequate thickness and firmness.
The phenomenon of getting worse of sensory characteristics of fermented milks during storage is commonly known and confirmed by many authors (Tamime & Robinson, 1999). It's mainly due to acidity growth, decomposition and evaporation of aroma substances, releasing of some proteolysis and lipolysis products, which influence negatively the taste and aroma, and shrinking of curd with whey release and getting worse of consistency.
However Bonczar et al. (1997) proved that sensory properties of kefir produced from ewe's milk did not significantly decreased during storage period. This fact was probably due to the relatively short time (14 days) they have done investigation.
The titratable acidity of investigated products ranged between 0,82 to 1,08%. Milk supplementation and storage time statistically influenced on this parameter. Kefir without solids addition (0) was characterized by significantly lower titratable acidity opposite to other products. The reason of this is that the level of titratable acidity depends on concentration of acids which were created during fermentation but also on the level of protein and acid carbonates and hydroxide. It was shown that during storage, acidity of all kinds of kefirs was growing up in concern of pH level and lactic acid concentration and reached the highest value at 21st day of storage. Statistically significant increase of this parameter was stated after 7th and 21st day of
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storage. That phenomenon is commonly known and it is a result of acidifying microflora activity (Tamime and Robinson, 1999).
Table 1.
Quality parameter of kefir during storage period
Parameter Kefir 0 Kefir SMP Kefir SMP/WPC Kefir WPC
1 day 7 day 21day 1 day 7 day 21day 1 day 7 day 21day 1 day 7 day 21day
Sensory 4,43 4,35 4,22 4,46 4,37 4,22 4,41 4,30 4,01 4,36 4,11 4,10
evaluation ± ± ± ± ± ± ± ± ± ± ± ±
[points] 0,15 0,17 0,06 0,09 0,05 0,22 0,14 0,07 0,17 0,16 0,13 0,06
4,39 4,43 4,61 4,43 4,45 4,68 4,45 4,47 4,69 4,42 4,46 4,68
pH ± ± ± ± ± ± ± ± ± ± ± ±
0,05 0,17 0,17 0,07 0,15 0,17 0,07 0,15 0,16 0,06 0,13 0,16
Lactic acid [%] 0,82 ± 0,07 0,91 ± 0,03 0,96 ± 0,03 0,91 ± 0,07 1,03 ± 0,04 1,08 ± 0,02 0,94 ± 0,11 1,04 ± 0,05 1,09 ± 0,01 0,98 ± 0,03 1,01 ± 0,02 1,07 ± 0,02
Acetaldehyde [mg/dm3] 1,16 ± 0,24 0,46 ± 0,10 0,76 ± 0,02 2,16 ± 0,46 0,72 ± 0,19 0,32 ± 0,12 2,12 ± 0,25 2,32 ± 0,29 0,56 ± 0,10 0,68 ± 0,21 1,00 ± 0,25 0,60 ± 0,13
Diacethyl [mg/dm3] 1,70 ± 0,18 0,86 ± 0,11 0,62 ± 0,06 1,20 ± 0,05 0,79 ± 0,02 0,65 ± 0,02 0,93 ± 0,09 1,07 ± 0,02 0,91 ± 0,03 1,22 ± 0,10 1,35 ± 0,09 0,88 ± 0,04
FFA [mEq/dm3] 5,30 ± 0,40 5,82 ± 0,31 5,94 ± 0,35 5,28 ± 0,29 5,70 ± 0,42 6,07 ± 0,39 6,03 ± 0,50 6,50 ± 0,44 7,21 ± 0,57 7,00 ± 0,39 7,25 ± 0,60 7,92 ± 0,64
"WW
determined by drainage method, determined
by centrifugal method
The pH of kefir was not affected by type of supplement used, so the pH value of all yoghurts was similar. It was due to the fermentation process was carried out until pH fixed at 4.6. During storage time pH of analysed kefir decreased. Statistically significant difference was noted after 21 day of storage. The typical pH value of fermented milks varies between 4,0 and 4,5. This scope of pH allows obtaining a proper consistency of products. The overflow this limits increased tendency to curd syneresis and result in to high level of curd firmness (Lucey, 1997, Chojnowski et al., 1997).
According to Polish Standard (PN-A-86061: 1983) the titratable acidity of kefir should be 0,8-1 %. Pijanowski (1984) investigated the acidity of kefir during time of maturation. He claimed that acidy of 1-day kefir is 0,8%, 2-day - 0,9%; 3-day - 1.01%. One of the most important factor affecting the growth of acidity of products is the composition of microflora of starter culture used (Jasinska et al 2001; Bonczar et al. 2002; Dankow et al. 2000).
The storage time statistically significantly influenced on level of both analysed volatile compound: diacethyl and acetaldehyde. The significance of reduction of concentration of both compounds was stated between 1st and 21st day of
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storage. Furthermore, the amount of acetaldehyde depended on type of kefir. Significantly higher level of this compound was characterized by kefir fortified with mixture of skim milk powder and whey protein concentrate.
Table 2.
Mean of the smallest squares from variance analysis concerning effect of kind of
Parameter Type of kefir Storage time (day)
0 SMP SMP/WPC WPC 1 7 21
Sensory evaluation [points] 4,30 4,35 4,24 4,19 4,42 A 4,27 4,12 A
pH 4,47 4,52 4,53 4,52 4,43 a 4,45 b 4,66 ab
Lactic acid [%] 0,73 ABC 1,01 A 1,02 B 1,02 C 0,79 a 0,99 A 1,05aA
Acetaldehyde [mg/dm3] 0,51 a 1,07 1,67 ab 0,79 b 1,34 A 1,13 0,56 A
Diacethyl [mg/dm3] 0,51 0,88 0,97 1,15 0,85 A 1,02 0,76 A
FFA [mEq/dm3] 5,69 a 5,68 b 6,58 ab 7,39 ab 5,90 A 6,32 6,97 A
A-F - statistical y highly significant differences between means (p < 0,01) marked by
the same letter in the rows
a-b - statistically significant differences between means (p < 0,05) marked by the same letter in the rows.
During kefir fermentation the concentration of diacethyl growing up until citrate are accessible in the medium. After the concentration of diacethyl reach the maximum, start process of its reduction to acetonin, which odourless. This reaction was catalysed by enzyme produced by lactic acid bacteria (Libudzisz, 1990). Results obtained by Pijanowski (1984) suggest that level of main volatile compounds in set type kefir is: 0,48 mg/L for diacethyl and 1,35 mg/L for acetaldehyde. According to Molska [1988] product is characterized adequate aroma when the concentration of diacethyl is about 2-3 mg per litre. If the level of this compound is below 1 mg/L, flavour of product is not enough sensible.
The substrate for acetaldehyde synthesis is citrate, pyruvate, lactose, aminoacids and nucleic acids (Libudzisz, 1990). Researches done by Jasinska et al. (2001) confirm that presence of yeast in kefir culture affect on higher level of acetaldehyde in product. Kefir produced with culture containing yeast was characterized by higher amount of acetaldehyde than products manufactured with culture without yeast in its microflora composition. The same authors observed that concentration of acetaldehyde significantly decreased after 2-weeks storage period. The level of reduction was varied between 21 and 37%. Similar results was obtained by Bonczar et al. (2002) and Molska (1988).
Composition of milk for kefir production significantly influence on free fatty acids level. Increasing of contribution of WPC in milk for kefir caused the rise of
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FFA level in product. Statistically significant differences were observed between control kefir (0/0) and kefir with SMP (1/0) opposite kefir with mix of SMP/WPC (1/1) and kefir with WPC (0/1).
After 21 day of storage amount of FFA significantly increased. Usually the growth of FFA level is affected by lipolysis but according to Beshkova et al. (2003) the source of FFA could be also the amino acids, converted to them by deamination process. This fact could explain relatively high level of FFA in analyzed kefirs, products with remnant amount of fat.
Conclusions
6. Experimental kefirs were characterized by high sensory quality. The best note received kefirs without addition of milk solid and products fortified with skim milk powder. The use of WPC slightly decreased sensory properties of kefirs.
7. Fortification of milk for kefirs with skim milk powder and/or whey protein concentrate caused growth of titratable acidity with stable level of pH value as well. During storage time significance increase of acidity was stated.
8. The storage time significantly decreased level of both analysed volatile compound: diacethyl and acetaldehyde. Significantly higher level of this compound was characterized by kefir fortified with mixture of skim milk powder and whey protein concentrate.
9. Increasing of contribution of WPC in milk for kefir caused the rise of FFA level in product. During storage concentration of FFA in all kefir systematically growth.
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Summary
The aim of the study was investigation of quality of fat-free, set-type kefir made at 11% (w/w) solid-non-fat level with addition of skim milk powder (SMP) and/or whey protein concentrate (WPC) blends. The ratio SMP/WPC in used blends was: 1/0; 1/1; 0/1. On 1st, 7th and 21st day of refrigerated storage kefir was analysed for sensory properties, titrable acidity, pH, free fatty acids (FFA), acetaldehyde, and diacethyl. Experimental kefirs were characterized by high sensory quality. The use of WPC slightly decreased sensory properties of kefirs. Fortification of milk for kefirs with skim milk powder and/or whey protein concentrate caused growth of titratable acidity with stable level of pH value as well. During storage time significant increase of acidity was stated. The storage time significantly decreased level of both analyzed volatile compound: diacethyl and acetaldehyde. Significantly higher level of this compound was characterized by kefir fortified with mixture of skim milk powder and whey protein concentrate. Increasing of contribution of WPC in milk for kefir caused the rise of FFA level in product. During storage period systematically growth concentration of FFA in all type of kefir.
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