Influence of transglutaminase treatment of skim milk on the formation of ε-(γ-glutamyl)lysine and the susceptibility of individual proteins towards crosslinking

Physicochemical and nitrogen solubility properties of Bacillus proteinase hydrolysates of sodium caseinate incubated with transglutaminase pre- and post-hydrolysis

Sodium caseinate (NaCN), hydrolyzed with Protamex, a Bacillus proteinase preparation, to 0.5, 1.3, and 17.5% degrees of hydrolysis, was incubated with transglutaminase (TGase) for 3, 42, and 290 min at enzyme/substrate ratios of 1, 1, and 10% (w/w), respectively, pre- and post-hydrolysis. The electrophoretic, reversed-phase high-performance liquid chromatography (RP-HPLC) and nitrogen solubility profiles of the modified products were investigated. Combinations of hydrolysis and incubation with TGase generated products displaying novel physicochemical and nitrogen solubility properties. Significant changes in sodium dodecyl sulfate (SDS) and urea polyacrylamide gel electrophoresis profiles were apparent in the modified caseinate samples. Extensive TGase cross-linking resulted in polymers that were unable to enter the resolving gel during SDS polyacrylamide gradient gel electrophoresis. Extensive combined enzymatic modification resulted in peptides eluting earlier on RP-HPLC than limited combined enzymatic modification or limited hydrolysis. Combination of enzymatic treatments resulted in significantly (P < 0.005) improved solubility around pH 4.6, compared to incubation with TGase or hydrolysis of NaCN alone.