Study of chymosin hydrolysis of casein micelles under ultra high pressure: Effect on re-association upon pressure release

The re-association of disintegrated casein micelles was investigated using a combined high pressure and enzymatic treatment with chymosin at 20 °C and 150 or 200 MPa. The amphiphilic, growth-limiting character of κ-casein was altered in the pressure-disintegrated state of the casein micelle. With increasing amounts of κ-casein being hydrolysed, less micellar surface can be covered with intact κ-casein after high pressure treatment. Therefore, larger particles with shifted surface-to-volume ratio were expected to occur with increasing degree of hydrolysis (DH) of κ-casein. Higher DH values led to larger reformed casein micelles. As compared with a control sample, the relative particle diameter showed a strong correlation to DH. This could be attributed to the re-association of caseins or micellar fragments forming micelles similar in structure as compared with native ones. Gelling similar to that in standard renneting, only occurred at DH levels above 0.80.