Heat-induced changes in the calcium sensitivity of caseins

Abstract

Abstract The calcium sensitivity of Na caseinate prepared from a serum protein-free casein micelle dispersion in synthetic milk ultrafiltrate, containing 4.8%, w/v, lactose and 5 mmol L −1 urea and heated at 130°C for 0–25 min decreased with heating. It is proposed that an increase in the net negative charge of the caseinates, due to heat-induced degradation of lysine and arginine, is responsible for the enhanced calcium stability of heated caseins. The Maillard reaction and urea–protein interactions appear to play an important role in the increased stability of heated caseinate towards calcium. The effect of protein charge on the heat stability of milk protein systems (Na caseinate 2.5%, w/v, protein in milk ultrafiltrate) at 140°C was investigated by chemical modification of the caseinate prior to assessment of heat stability. Heat stability increased with the modification of lysine, arginine and carboxyl residues. The increased heat stability of Na caseinate with modified lysine and arginine residues may be due to an increase in the net negative charge on the caseinate, while the increased stability of caseinate with modified carboxyl residues may be related to a reduction in heat-induced crosslinking of protein.