Crosslinking of whey protein by transglutaminase.

Guinea pig liver transglutaminase (EC 2.3.2.13) was used to enzymically crosslink the whey protein alpha-lactalbumin, beta-lactoglobulin, blends of these protein fractions, whey proteins in powdered whey, and whey proteins in modified powdered whey. Transglutaminase actively crosslinked whey proteins over a wide pH range (6.5 to 8.0). Crosslinking gradually increased with increased incubation time to 4 h. Crosslinking was negligible with transglutaminase after 4 h of incubation. Reconstituted commercial whey and modified whey powders contained sufficient Ca2+ for crosslinking by .92 units transglutaminase/ml of reconstituted whey powder (2% protein) and modified whey powder solutions (1 to 5% protein). Reconstituted whey and modified whey powder (35% protein) served as protein sources for crosslinking by transglutaminase without further adjustment of pH or Ca2+. Dithiothreitol was required to crosslink the whey protein.