The gel strength and viscosity of pure gelatin powder are important indicators to measure the quality of gelatin, and its flavor directly affects the development and application of gelatin.
Gel strength is a measure of the hardness, stiffness, strength and compressibility of gelatin at a specific temperature, which are all affected by the concentration and molecular weight of the gelatin. The gel strength of fish gelatin is positively correlated with the content of α chain in fish skin gelatin, that is, the more α chain content, the higher the gel strength. The gelatin strength of the gelatin extracted from abalone skin was between 243 and 256g, and they found that the more peptide chains in the skin, the weaker the gel strength. The gel strength of the gelatin extracted from grass carp was 267 g, and the other ones were 180.76 g, 263 g, and 229 g, respectively. In contrast, gelatin extracted from tropical fish yellowfin, tuna and fin skins had higher gel strengths of 426g and 460g, respectively. The researchers noted that using glutaraldehyde and cross-linking fish gelatin greatly improved its gel strength. Related studies have also shown that the gel strength of fish gelatin can be improved by adding plasticizers.
The viscosity of gelatine fish powder is affected by temperature, concentration, pH, etc., while the concentration and type of acid have a significant effect on the viscosity of gelatin solution. With the increase of acid concentration, the viscosity of gelatin first increases and then decreases. When the acid concentration is too high, it may lead to an increase in the content of small molecular weight proteins in fish gelatin powder, thereby reducing its viscosity. The effect of hydrogen peroxide addition and its concentration, extraction temperature, extraction time and other factors on the viscosity of tilapia skin gelatin, and the viscosity of 6.67% tilapia skin gelatin was measured to be 6.14mPa·s when the extraction temperature was 60℃. In addition, the viscosity of fish gelatin solutions can be increased by adding polysaccharides such as carrageenan.
Almost all studies on the extraction and properties of pure gelatin powder have shown that compared with terrestrial mammalian gelatin, fish gelatine powder has a more or less fishy odor, which limits its application to some extent. After research, it was found that fish gelatin can be denatured by modification, thereby reducing or eliminating its fishy smell. For example, the Japanese patent is to chemically modify fish gelatin derivatives to retain the excellent properties of fish gelatin for moisturizing and lubricating the skin, while eliminating the fishy smell of fish. By studying the effect of melting temperature on the sensory properties of fish skin gelatin, it was found that fish skin gelatin released the desired flavor and aroma more easily than pig skin gelatin. Since fish skin gelatin can release volatile aroma well, it can be used for the development of new products.