Fortification of milk protein content with different dairy protein powders alters its compositional, rennet gelation, heat stability and ethanol stability characteristics

Skim milk (SM) was fortified from 3.3 to 4.1% protein using different milk protein powders: skim milk powder (SMP), native phosphocasein (NPC), calcium-reduced phosphocasein (CaRPC), sodium caseinate (NaCas) or calcium caseinate (CaCas). Compared with SMP or NPC, fortification with NaCas and CaRPC, and to a lesser extent CaCas, resulted in milk samples having higher proportions of non-sedimentable casein and calcium, and lower- and higher-levels of κ- and αS1-casein, respectively, as a proportion of non-sedimentable casein. These changes coincided in milk samples fortified with NaCas, CaRPC or CaCas failing to undergo rennet-induced gelation, and having higher heat stability in the region 6.7–7.2 and ethanol stability at pH 6.4. The study demonstrates that the aggregation behaviour of protein-fortified milk samples is strongly influenced by the degree of mineralisation of the protein powder used in fortification, which affects the partitioning of casein and calcium in the sedimentable and non-sedimentable phases.