Effect of kappa-casein dissociation on rennet-induced gelation in high-heated milk protein
2024
Ono, W. | Asada, Y. | Oka, D. | Tsujii, Y. | Noguchi, T.
The first steps of cheese making involves the coagulation of caw [raw] milk using the coagulating enzyme rennet, resulting in gel formation. However, it is known that when high-temperature sterilized milk, such as at 130 deg C for a few seconds, is used as the raw material of cheese making, the denaturation of milk proteins becomes a significant factor, leading to poor rennet-induced gelation. Therefore, traditional cheese making has relied on the use of raw milk or low-temperature pasteurized milk. In the interest of safety, the authors of this study are conducting research aimed at developing a technique for cheese production from high-temperature sterilized milk. In this study, authors investigated the impact of heat-induced denaturation of milk proteins, specifically the dissociation of kappa-casein from the casein micelles caused by disulfide bonds between kappa-casein and whey proteins, on the rennet-induced gelation. Fresh raw milk was defatted and centrifuged to obtain undenatured casein micelles. Whey protein isolate solution (protein was included to 0-0.78%) was then added to the casein micelles, followed by heating at 80 deg C for 30 minutes to induce protein denaturation. The denatured casein micelles were subsequently isolated through centrifugation of the suspension and dispersed in a buffer solution mimicking the mineral composition of milk. The rennet gel was prepared by addition of 0.018 IMCU/mL of rennet to casein micelle dispersions and incubated at 32 C for 0-180 minutes. The gel properties were evaluated using a creep meter. The results demonstrated that the degree of kappa-casein dissociation increased with increasing whey protein concentration, and a higher degree of kappa-casein dissociation corresponded to poorer rennet-induced gelation.
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