Tianjin Key Laboratory of Food Biotechnology, College of Biotechnology and Food Science, Tianjin University of Commerce, Tianjin 300134, China.
Mengniu Hi-Tech Dairy (Beijing) Co., Ltd., Beijing 101107, China.
Molecules. 2023 Mar 6;28(5):2396. doi: 10.3390/molecules28052396.
Ultra-high-pressure jet processing (UHPJ) is a new non-thermal processing technique that can be employed for the homogenization and the sterilization of dairy products. However, the effects on dairy products are unknown when using UHPJ for homogenization and sterilization. Thus, this study aimed to investigate the effects of UHPJ on the sensory and curdling properties of skimmed milk and the casein structure in skimmed milk. Skimmed bovine milk was treated with UHPJ using different pressures (100, 150, 200, 250, 300 MPa) and casein was extracted by isoelectric precipitation. Subsequently, the average particle size, Zeta potential, contents of free sulfhydryl and disulfide bonds, secondary structure, and surface micromorphology were all used as evaluation indicators to explore the effects of UHPJ on the structure of casein. The results showed that with an increase of pressure, the free sulfhydryl group content changed irregularly, while the disulfide bond content increased from 1.085 to 3.0944 μmol/g. The content of α-helix and random coil in the casein decreased, while the β-sheet content increased at 100, 150, 200 MPa pressure. However, treatment with higher pressures of 250 and 300 MPa had the opposite effect. The average particle size of the casein micelles first decreased to 167.47 nm and then increased up to 174.63 nm; the absolute value of Zeta potential decreased from 28.33 to 23.77 mV. Scanning electron microscopy analysis revealed that the casein micelles had fractured into flat, loose, porous structures under pressure instead of into large clusters. After being ultra-high-pressure jet-processed, the sensory properties of skimmed milk and its fermented curd were analyzed concurrently. The results demonstrated that UHPJ could alter the viscosity and color of skimmed milk, shortening curdling time from 4.5 h to 2.67 h, and that the texture of the curd fermented with this skimmed milk could be improved to varying degrees by changing the structure of casein. Thus, UHPJ has a promising application in the manufacture of fermented milk due to its ability to enhance the curdling efficiency of skimmed milk and improve the texture of fermented milk.
超高压射流处理（UHPJ）是一种新的非热加工技术，可用于乳制品的均化和灭菌。然而，当 UHPJ 用于均化和灭菌时，对乳制品的影响尚不清楚。因此，本研究旨在研究 UHPJ 对脱脂牛奶的感官和凝乳特性以及脱脂牛奶中酪蛋白结构的影响。使用不同压力（100、150、200、250、300 MPa）对脱脂牛乳进行 UHPJ 处理，然后通过等电沉淀提取酪蛋白。随后，平均粒径、Zeta 电位、游离巯基和二硫键含量、二级结构和表面微观形态均用作评估指标，以探讨 UHPJ 对酪蛋白结构的影响。结果表明，随着压力的增加，游离巯基含量呈不规则变化，而二硫键含量从 1.085 增加到 3.0944 μmol/g。酪蛋白中的α-螺旋和无规卷曲含量减少，而β-折叠含量在 100、150、200 MPa 压力下增加。然而，在 250 和 300 MPa 更高压力下处理则有相反的效果。酪蛋白胶束的平均粒径先减小到 167.47nm，然后增加到 174.63nm；Zeta 电位的绝对值从 28.33 降低到 23.77mV。扫描电子显微镜分析表明，在压力下，酪蛋白胶束断裂成扁平、松散、多孔的结构，而不是形成大的聚集体。超高压射流处理后，同时分析了脱脂牛奶及其发酵凝乳的感官特性。结果表明，UHPJ 可以改变脱脂牛奶的粘度和颜色，将凝乳时间从 4.5h 缩短至 2.67h，并且通过改变酪蛋白的结构，可以在不同程度上改善用这种脱脂牛奶发酵的凝乳的质地。因此，由于 UHPJ 能够提高脱脂牛奶的凝乳效率并改善发酵牛奶的质地，因此在发酵牛奶的制造中具有广阔的应用前景。
