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 degrees C and 150 or 200 MPa. The amphiphilic, growth-limiting character of kappa-casein was altered in the pressure-disintegrated state of the casein micelle. With increasing amounts of kappa-casein being hydrolysed, less micellar surface can be covered with intact kappa-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 kappa-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. (C) 2011 Elsevier Ltd. All rights reserved.