Functional properties of Bacillus proteinase hydrolysates of sodium caseinate incubated with transglutaminase pre- and post-hydrolysis

The effects of hydrolysis with Protamex (a Bacillus proteinase), cross-linking with microbial transglutaminase, and combinations of these treatments on the functional properties of sodium caseinate (NaCN) were investigated. Higher (P < 0.005) emulsifying activity index (EAI) values were observed between pH 4.0 and 10.0 on hydrolysis of transglutaminase cross-linked NaCN to 0.5% degree of hydrolysis (DH) compared to either the 0.5% DH hydrolysate, the cross-linked NaCN or unmodified NaCN control. Reversing the order of modification (cross-linking after hydrolysis to 0.5% DH) generated a product which displayed 1433% foam expansion (FE) at pH 6.0, compared to 735% FE for the control. Cross-linking with transglutaminase after hydrolysis to 1.3% DH resulted in significant improvements (P < 0.005) in EAI at low pH, compared to control. In addition, the latter sample exhibited greater FE than the control between pH 3.0 and 10.0 (P < 0.005). Extensive transglutaminase-catalysed cross-linking of NaCN per se resulted in increased viscosity (P < 0.005) at alkaline pH.