Proteomic analysis of chymosin and microbial transglutaminase-induced coagulation of milk proteins

• Main Authors: Pan, Peihsin, 潘姵妡
• Other Authors: Hsieh, Jungfeng
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/86999530404144195071

碩士 === 輔仁大學 === 食品科學系 === 99 === Milk, which contains 3.3% proteins, is a valuable nutrient source for humans. Milk proteins are classified into two groups, 80% of caseins (αS1-, αS2-, β-, and κ-caseins) and 20% whey proteins (β-lactoglobulin, α-lactalbumin and bovine serum albumin). The objective of this study was to analyze the effects of milk proteins affected by chymosin and microbial-transglutaminase by proteomic approach. The addition of chymosin (0.006 units/mL) to milk caused the milk proteins coagulated after a 3 h incubation period at 30oC. Approximately 90% of the milk proteins were coagulated into the milk pellet fraction, and the total protein in the milk decreased from 29.8 mg/mL to 3.4 mg/mL. SDS-PAGE analysis showed that all milk caseins were the major substrate for chymosin. Two-dimensional electrophoresis analysis indicated that casein isomers and a fraction of the β-lactoglobulin and bovine serum albumin were coagulated following incubation with chymosin. These results suggested that caseins were coagulated by chymosin, and a fraction of the β-lactoglobulin and bovine serum albumin were co-coagulated by the caseins. Besides, the addition of varying amount of microbial-transglutaminase (0.25-2.0 units/mL) to milk caused the milk proteins polymerized after a 3-h incubation period. SDS-PAGE analysis showed that inter- and/or intramolecular crosslinking occurred in the caseins of microbial-transglutaminase-containing milk and components with higher molecular weights were observed, and the content of these higher molecular weights proteins increased with time. Two-dimensional electrophoresis analysis indicated that isomers of β-, κ-caseins, a fraction of bovine serum albumin, αs1- and αs2-caseins, β-lactoglobulin and α-lactalbumin in milk were polymerized by microbial-transglutaminase. In addition, microbial-transglutaminase-induced polymerization of β- and κ-casein isomers occurred earlier than for other milk proteins. In conclusion, the mechanism of individual milk proteins with chymosin and microbial-transglutaminase is recognized clearly by proteomic approach. Therefore, the proteomic approach could be utilized in dairy industry to monitor the changes of proteins in dairy products and maintain product quality in the future.