| Summary: | 碩士 === 輔仁大學 === 食品科學系碩士班 === 103 === Milk contains 2.8% proteins which is an important source of nutrition for humans. Milk proteins composed of 80% caseins (αS1-, αS2-, β- and κ-casein) and 20% whey proteins (α-lactalbumin, β-lactoglobulin, and serum albumin). Glucono-δ-lactone (GDL) and propylene glycol alginate (PGA) are widely as food grade additives. The objective of this study was to analyze the GDL and PGA-induced coagulation of milk proteins by proteomic approach. The addition of GDL (0.5 M) to milk caused the milk proteins coagulated after a 1 h incubation period at 30oC. Approximately 90.7% of the milk proteins were coagulated into the milk pellet fraction, and the total protein in the milk decreased from 29.2 ± 1.1 mg mL-1 (control) to 2.7 ± 1.1 mg mL-1. The texture profile analysis showed that cheese-treated products (5.0 ± 0.4 N) by 0.5 M GDL direct acidification were similar with commercial cheese (5.2 ± 0.2 N). SDS-PAGE analysis showed that caseins and a portion of β-LG were coagulated because of GDL. Besides, the addition of PGA (1%) to milk caused the milk proteins coacervated after a 1 h incubation period at 30oC. Approximately 75.8% of the milk proteins were coagulated into the milk pellet fraction, and the total protein in the milk decreased from 29.2 ± 0.6 mg mL-1 to 7.0 ± 0.3 mg mL-1. SDS-PAGE analysis showed that caseins and a portion of serum albumin, α-LA and β-LG were coagulated by hydrophobic association of PGA. Moreover, the scanning electron microscope images indicated that milk protein molecules constructed by fine strands in a dense arrangement with the concentration of GDL or PGA. Two-dimensional electrophoresis analysis indicated that milk proteins were coagulated by increasing GDL or PGA concentrations. In conclusion, the mechanism of individual milk proteins with GDL and PGA is recognized clearly by proteomic approach. Therefore, the proteomic approach could be utilized in food industry to predict the changes of proteins in dairy products in the future.
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