| Summary: | 碩士 === 輔仁大學 === 食品科學系碩士班 === 107 === Milk proteins are composed of 80% caseins (αS1-, αS2-, β- and κ-casein) and 20% whey proteins (α-lactalbumin, β-lactoglobulin, and bovine serum albumin). Transglutaminase (TGase) and chymosin are widely used food grade additives. TGase is an enzyme that catalyzes the acyl transfer reaction between lysine residues and glutamine residues, which causes ε-(γ-glutamyl)lysine covalent bonds with intra-and inter-molecular cross-linking to form in milk proteins. Chymosin is the principal protease used for cheese making because it has highly specific milk-clotting activity relative to its proteolytic activity. Ultrasound transmits high intensity and frequency sound waves, which results in violent collision between particles in liquid. Thus, the objective of this report was to analyze the influence of transglutaminase and chymosin treatment on the coagulation of individual milk protein. The addition of TGase (6.0 unit/mL) caused the individual milk protein to polymerize and the components with higher molecular weights were observed after 0, 10, 20, 40 and 60 min incubation at 30°C with ultrasound. This ultrasound treatment has an operating frequency of 20,000 Hz, power of 400 W and amplitude 20%. Furthermore, the particle aggregation of proteins were observed by using nanoparticle analyzer and transmission electron microscopy. SDS-PAGE analysis showed that the intensities of α-casein, β-casein and κ-casein noticeably decreased to 5.6 ± 0.3, 3.9 ± 0.0 and 26.0 ± 1.1%, respectively, when both of ultrasound and TGase were used in combination. Besides, it could observe the individual milk proteins aggregated so that the particle size increased after ultrasound treatment. Otherwise, the milk sample and individual milk protein with/without chymosin (0.03 units/mL) were incubated at 30 °C for 0, 1, 2, and 3 hr. The sample were observed by using nanoparticle analyzer and matrix assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI-TOF MS). MALDI-TOF MS analysis showed the molecular weights of αs1-casein was 23.5 kDa and a portion of 20.8 kDa and β-casein were mostly decreased to 22 kDa incubated with chymosin for 3 hr. These results demonstrate that the combination of TGase and ultrasound induced the polymerization of milk protein faster than that of only TGase used. Not only κ-casein but also α-casein and β-casein both are hydrolyzed by chymosin.
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