Characteristics of Heated Mixed Soy Protein Isolate and Sodium Caseinate

Abstract

This study investigated the influences of protein concentration (10-15% w/v), protein ratio, pH (3.0-5.4), salt types and concentrations (Na lactate 0-250 mM or Ca lactate 0-60 mM) on the characteristics of heated mixed soy protein isolate (SPI) and sodium caseinate (SCN). Heat treatment at
80°C for 30 min did not alter the MW profiles of the SCN or SPI-SCN mixture. However, further addition of Na lactate and Ca lactate to the heated protein suspensions resulted in a high degree of aggregation observed as turbidity results, particularly in the suspensions containing a high ratio of SCN at pH 3.0 (p<0.05). Salt-mediated sulfhydryl-disulfide interchange was involved in the aggregation of heated mixed protein even with an acidic pH. The second stage heat treatment (at 80°C for 30 min) of the salt-induced aggregates, at a protein concentration below the minimum concentration required to form gel (10% w/v), resulted in the formation of a stable suspension, sedimentation, a viscous suspension or gelation depending on the protein ratio, pH and salt concentration. Such two-stage heating process applied to the SPI-SCN mixture could be used to achieve both functional properties and nutritional qualities, which are desirable characteristics of high protein diets.