In general, the decrease in the digestibility of sodium
caseinate caused by severe heating was probably due to
heat-induced protein}protein interactions or cross-links,
as evidenced by the smearing of major bands in the
SDS-gel electrophoretograms (Fig. 1: slots 2 and 3) and
changes in protein structure which prevent easy access of
proteolytic enzymes to casein by steric hindrance and
slow down or even prevent proteolytic attack. The damage
to protein quality (reduction of PER) of Na caseinate
was probably due to destruction of methionine and other
sulphur-containing amino acids, e.g. by oxidation, alkylation
or other interactions during heating.
Fig. 1. SDS-PAGE of sodium caseinate (slot 1) and sodium caseinate
heated at 120 (slot 2) or 1323C (slot 3) for 60 min. Proteins loads: 120 lg.