Gelation properties of casein micelles during combined renneting and bacterial fermentation: Effect of concentration by ultrafiltration

The objective of this study was to determine the effect of concentration of milk by ultrafiltration on the development of the gel structure induced by a combination of acidification (with mesophilic cultures) and rennet. As the initial aggregation was driven by rennet, all samples showed a similar initial gelation point and differences were observed after, during further acidification. All samples reached a maximum elastic modulus (G′) value, and then a breakdown of the structure occurred at a pH ranging from 6 to 5.6, depending on protein concentration. At pH ∼5.0 a maximum of tan δ (where δ is the phase angle) was observed, and the pH maximum depended on the concentration level. These differences were due to different rates of calcium release. This study clearly describes the molecular details occurring during mixed coagulation and allows for a better understanding of the processes occurring during making of quark-type cheeses.