Pressure-dependent changes in physicochemical characteristics of whey protein and casein: Structure and function...

As an emerging non-thermal processing technology, Ultra-high-pressure jet (UHPJ) processing has the effect of homogenizing and sterilizing materials concurrently. The UHPJ-treated skimmed milk was employed in this study to reveal the impact of pressure as the primary factor on protein structure and physicochemical properties. The results showed that with the increase of jet pressure, whey protein's endogenous fluorescence intensity increases, and casein's exogenous fluorescence intensity increases. The structure of casein tends to be loose, in contrast to the aggregation tendency of whey protein. After pressure treatment at 100-200 MPa, the thiol content peaked at 0.11 μmol/g. The content of α-helix increased to 17 %. The emulsifying stability of skim milk improved to 18.48 m²/g, and its foaming expansion index and foaming stability index attained values of 27.65 % and 24.9 %, respectively. The digestion rate of milk proteins processed at 200 MPa was the highest in the gastric digestion stage and relatively high in the intestinal digestion stage. At 250 and 300 MPa, the SDS - PAGE electrophoresis results showed that the loose binding of casein and 18 kDa β-Lactoglobulin under high pressure was separated. The instantaneous decompression characteristic of UHPJ tends to destabilize the emulsion system by disrupting the formed interfacial layer, making the 250 and 300 MPa pressure range unfavorable for emulsion stabilization. This study will provide a scientific basis for applying UHPJ in the dairy industry.