Heat-induced and Transparent Gel Prepared from Hen Egg Ovalbumin in the Presence of Salt by a Two-step Heating Method

Abstract

Heat-induced transparent gels from ovalbumin solution can be prepared, but only at low ionic strength, which limits their practical uses. We describe here their preparation at different salt concentrations. Ovalbumin solution (5% w/v) was heated at 80°C, pH 7.0, for 1 hr without salt to give a transparent solution. This solution was cooled and reheated with 0.2 m NaCl, which converted it to a transparent gel. At higher NaCl concentrations, the gel was harder and slightly turbid. We examined the change in the ovalbumin molecule when heated without salt. Gel filtration showed that with heating, the amount of ovalbumin monomers decreased and another peak appeared. After 30 min of heating, there was only one peak. This was a soluble aggregate. SDS- HPLC showed that this soluble aggregate was composed of monomers and oligomers connected by a disulfide bridge or bridges. A conformational change was detected with the difference spectrum. The number of sulfhydryl residues decreased slightly.