الملخص الإنجليزي
Moisture sorption isotherm and mechanical characteristics of gelatin gels extracted from grouper skin, and commercial bovine and porcine. The gelatin yield obtained from grouper fish skin was 26.4% as expressed in grams of dry gelatin per 100 g of dry solids in skin. The gelling and water sorption properties of gelatin extracted from grouper skin were measured and compared with gelatin from mammalian sources (bovine and porcine). The mechanical characteristics (hardness, firmness, toughness, and modulus) of 10% gels of gelatin from fish skin, determined from one cycle compression, were significantly lower compared to the other sources of gelatin gels. Bovine and porcine gels did not show any significant difference in their mechanical characteristics. In one cycle, 80% compression was used in order to fracture the samples. A compression of 40% was used in two compression-decompression cycles in ordered to avoid gel fracture. Hardness of fish and mammalian gelatin increased significantly as the concentrations of gels increased. The hardness of bovine gelatin gel was highest (harder) followed by porcine then fish gelatin gels. Cohesiveness of 20% bovine and 10% fish skin gelatin gels were the highest and lowest, respectively and in the cases of other samples at different concentrations there were no significant differences. Adhesiveness of bovine gelatin gels decreased significantly as the concentration of gels was increased. Adhesiveness of porcine gels showed no significant differences for different concentrations. The fish skin gelatin gels at 10% concentration showed significantly lower adhesive properties compared to the 20 and 30% concentrations. Fish skin gelatin gels at 10% showed the lowest springiness value compared to all other samples. In the cases of other samples there were no significant differences in the springiness of different types of gels with varying concentration. In the case of bovine and fish gels at 10%, resilience was significantly increased compared to the 20 and 30% concentration gels. Bovine and porcine gelatin gels showed higher gumminess and chewiness compared to fish gelatin gels at the same level of concentration. The gels prepared from different sources did not show any generic trends when all mechanical attributes were considered. Dynamic Vapor Sorption (DVS) showed a hysteresis between adsorption and desorption for bovine gelatin, which started from water activity of 0.7 and below, whereas hysteresis in fish skin gelatin started at water activity of 0.6.
The values of BET-monolayer water content of gelatin from bovine, porcine and fish skin were
8.00, 8.88 and 6.11 g/100 g solids, respectively.
