Effect of transglutaminase and acidification temperature on the gelation of reconstituted skim milk

Effects of transglutaminase (TG), acidification temperature and total milk solids level on the acid gelation of skim milk were investigated. Despite similar acidification kinetics, TG-treated milk acidified at ≥35 °C showed differences in elastic modulus (Gʹ) with acidification time, particularly by inhibiting the formation of the peculiar shoulder (Gʹ _shoulder ) observed at an early stage of gelation in the control milk. Regardless of the milk solids content, the G’ _shoulder was absent in both types of milk at 30 °C. However, control milk above 2.5% (w/w) milk solids showed the G’ _shoulder at 45 °C. G’ _shoulder is proposed as the transition from the first increase in Gʹ, due to aggregation of soluble protein complexes at the early stage of acidification, to the second, due to further aggregation of casein micelles (and aggregated soluble complexes) as acidification progresses. The G’ _shoulder was absent in acidified TG-treated milk due to the lack of soluble protein complexes containing caseins.