Incorporation of soy protein isolate and egg-white protein to improve nutritional value and hardness of gelatin gels for the elderly

Abstract

This study aimed to determine the effects of globular proteins (soy protein isolate and egg-white protein) incorporation on the physicochemical properties of gelatin gels for the elderly. Stepwise gelation was considered through primarily heat-induced gelation of the globular proteins and following cold-set gelation of gelatin during cooling. Control gelatin gel was prepared with porcine skin gelatin at 6% (w/v) concentration. For mixed gelatin gels (treatment), two different mixing ratios (gelatin:globular protein) were considered as 1:1 and 1:2, respectively, by replacing the portion of porcine skin gelatin powder with the two globular proteins. Similar processing yield was found (p>0.05), but there was the small numerical difference in protein content (6.21–6.47 g/100 g) between treatments (p<0.05). At 1:2 mixing ratio, the content of essential amino acids was significantly higher than that of control. Moreover, incorporating soy protein isolate and egg-white protein at the 1:2 mixing ratio could noticeably reduce the hardness of gelatin gels (p<0.05). Results for the thermal properties, X-ray diffraction, and microstructure indicated that gelatin might be predominantly contributed to forming the microstructure of mixed gelatin gels. Taken together, the mixed gelatin gels at 1:2 mixing ratio could achieve the both protein content (over 6 g/100 g) and hardness (gums intake level, below 20,000 N/m2) criteria of the Korean Industrial Standard for elderly foods. Therefore, the stepwise incorporation technique of globular proteins could be useful to manufacture a gelatin gel with high-essential amino acids and a soft texture for the elderly.