| China has the richest freshwater fish resources around the world, more than700species, including40-50commercially species. Bighead carp (Aristichthys nobilis), distributed in South and East China, is one of the most commonly commercially produced fresh water fish in China. The fish meat and skin are used for human food, leaving almost50-70%wastes such as bone and scale. With the rapid expansion of the fish food process industry in Southeast China, the wastes disposal poses a big environmental challenge. The extraction of gelatin or other bio-materials from these production wastes might be a promising solution in terms of both reducing environment pollution and increasing the economic efficiency of the industry.Nutritional components of bighead carp scale were analyzed with protein60.19%. ash25%, and moisture13.40%. Considering the difficulty to extract the collagen together with the existence of hydroxyapatite in ash. decalcification process was necessary before extraction.17.56%of Calcium was decalcified with the optimal extraction conditions of0.4mol/l EDTA-2Na,30:1ratio of solution to sample and8h.Optimal collagen extracting processes using acetic acid and pepsin were also analyzed during the study. The results showed that extraction rate for collagen reached1.31%±0.31%under the condition of acetic acid concentration of1250U/g, liquid to solid ratio of30:1and extraction time of2hours and pepsin concentration of0.5%. liquid to solid ratio of30:1and extraction time of2hours for the optimized conditions for pepsin extraction method with the highest extraction rate of1.79±0.28%.Primary and secondary structures of acid-soluble collagen and pepsin-solubilized collagen were analyzed in the study. The amino acid composition analysis showed that the content of Glycine is over24%which is the most abundant component, and poline, glutamic acid, alanine, arginine are of significant proportions. Structure of a helix was determined by using infrared scan. Denatured temperature of protein was32.5℃which was higher than the other kinds of collagen of fish species.Gelatin can be gained after hydrolyzing the denatured collagen. The process conditions for gelatin extraction from scale are identified by using Response surface experiments. Under the conditions of extraction temperature of46.98℃,2h, pH4.00and enzyme concentration of547U/g, the maximum gel strength can reach318±7g (p<0.01) comparing to (216±3g, p<0.01) using hot water method.The comparison study of gelatin from scale and pigskin indicates high significant composition differences of threonine, isoleucine, methionine and phenylalanine and lysine and significant differences of hydroxyproline, glycine, alanine. Bighead carp scale gelatin showed lower imino acid (Proline and Hydroxyproline) content (20.75±0.82%) than pig skin gelatin (24.01±0.70%). Assessment on dynamic viscoelastic properties indicated that bighead carp scale gelatin had better gelling ability and lower thermo-stability than pig skin gelatin.Using papain and pepsin, we got the bighead carp scale gelatin hydrolysate which can inhibite the activity of angiotensin converting enzyme (ACE), with ICsoof864μg/ml. After ultrafiltration, we got the fraction of molecular mass lower than5KD with IC50of331μg/ml. Then the fraction of molecular mass lower than5KD was isolated by Sephadex G25to afford one part with IC50of107μg/ml.We studied the technology of improving the flavor of bighead carp hydrolysate by Maillard reaction. The optimal conditions for sensory evaluation are9.5for reaction pH,120℃for reaction temperature,3.75%for the glucose, and100min for the time of reaction. Amino acid analysis shows that the main amino acids changed much during the reaction are:arginine (reduced74.44%), lysine (reduced65.50%), and tyrosine (reduced42.50%), which may be the key amino acids taking part in the maillard reaction. |
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