Heat-induced changes in the nutritional properties of sodium caseinate

The effects of heating 5% (w/v) Na caseinate solutions in the temperature r ange 120-140 degrees C for 30 or 60 min at pH 7.0 on the nutritional proper ties of the protein were investigated. Protein efficiency ratio (PER) was s lightly but significantly (P < 0.05) reduced by both heat treatments from 2 .8 for the control (unheated Na caseinate) to 2.6 (120 degrees C treatment) and 2.4 (132 degrees C treatment). The digestibility in vivo in rats of th e sample heated at 132 degrees C (94.0%) was slightly lower than that of th e control (95.3%), but there was no significant difference between the cont rol and the sample heated at 120 degrees C (94.7%). Digestibility in vitro by trypsin plus chymotrypsin was lower for both heated samples than for the control. Available lysine and methionine contents were reduced slightly in the heated samples. The results suggest that the decrease in PER of Na cas einate on heating may be due mainly to loss of available methionine. The re activity of caseinate to TNBS was increased on heating, which indicates tha t some proteolysis occurred. SDS-polyacrylamide gel electrophoretograms of treated samples showed that several peptides were formed due to the heat-in duced proteolysis. (C) 1999 Elsevier Science Ltd. All rights reserved.