The inhibitory roles of native whey protein on the rennet gelation of bovine milk

- The effect of native whey protein on rennet gelation was investigated.
- A wide range of whey protein:casein ratios were tested using microfiltration powders.
- Native whey protein inhibited the chymosin enzyme in rennet, delaying the gelation.
- Native whey protein also presents a physical barrier that slowed subsequent gelation.

Rennet gelation is used to produce many types of cheese. The effect of native whey protein on rennet gelation kinetics was investigated. Milks with a wide range of whey protein:casein (WP:CN) ratios (with standardised casein concentrations) were made from powders produced by microfiltration. Measurements of casein macro peptide release showed that native whey protein inhibited the enzymatic action of chymosin, which delayed the onset and reduced the subsequent rate of gelation. Experiments in which increased chymosin concentrations compensated for the inhibition, demonstrated that other factors also contributed to the reduced gelation rate. Neither an increase in viscosity nor a reduction in soluble calcium was responsible, leading to the conclusion that in addition to inhibiting chymosin, native whey proteins present a physical barrier to para-casein aggregation. This study demonstrates and explains how casein-enriched retentates from microfiltration gel faster than regular cheese milk that contains higher amounts of native whey protein.