Study On Mechanism Of Extensive Hydrolysis Of Low-valued Fish

Autolysis of low-valued fish and the extensive hydrolysis mechanism during the extensive hydrolysis of low-valued fish with complex protease was studied, using nitrogen recovery, degree of hydrolysis, amino acids composition analysis, TCA insoluble nitrogen and gel exclusion chromatography. The biochemical indices, like taste and color of low-valued fish hydrolysate, total basic volatile nitrogen, TMA, TBA value and free fatty acid was monitored for 42 h, with aim for industry utilization.The low-valued fish contained 79.97% of moisture, 16.8% of protein (N×6.25),0.40% of fat and 2.24% of ash. Autolysis of low-valued fish was caused mainly by trypsin, chymotrypsin and carboxypeptidase. The bacteria courts plummeted from 1.4×106 to 200cfu/ml in 12 h and stayed in this level during the rest of hydrolysis. The optimal condition for autolysis of low-valued fish is pH 6~7 at 55℃. Ca2+ activiated endogenous protease, however, Zn2+ and EDTA inhibited slightly the autolysis of low-valued fish. The protein recovery of autolysate of low-valued fish is fairly high, up to 78.51%, however, Degree of Hydrolysis of autolysis of low-valued fish is only 27.4%.The optimal conditions for extensive hydrolysis of low-valued fish were 55℃, pH7.0, 42h, 476U/g Flavourzyme, 447U/g Alaclase and 59.5U/g pancreatin, 0.1% NaSO3 and 0.1% CaCl2,. The condition under this study resulted in 92.96% of protein recovery and 63.68% of degree of hydrolysis.High molecular weight fraction (>10700 Dalton) was disappeared after a 3h of hydrolysis; Molecular weight fraction ranged from 6214 to 8159 Dalton was markedly decreased and Low molecular weight fraction (<2512 Dalton) accumulated gradually during the whole hydrolysis. Obviously, insoluble protein was first broke into amino acids and large soluble fragments which were in turn hydrolysed into smaller peptides and amino acids. The slow down of hydrolysis rate was due to decrease in specific peptide bonds available for enzyme action.The release of soluble peptide is dominant in the first three hours, the amino acid is cleaved from soluble peptide consequently during the rest of hydrolysis. On the contrast, total acid and total carbonhydrate were released in the first three hours and decreaed during the rest of hydrolysis. The change of taste of hydrolysate was caused mainly by amino acids and peptides. Mineral and organic acid also played a part in the taste of low-valued fish hdydrolysate. The increase in total volatile basic nitrogen (TVBN) was caused by endogenous deaminase. Heat treatment after autolysis of 6h, along with addition of exogenous protease could effectively inhibited increase in TVBN without debased nitrogen recovery and degree of hydrolysis. Decrease in pH of hydrolysate from 7.0 to 6.25 was due to release of amino acids and small peptides.Mailard reaction could effectively changed the flavor of low-valued fish hydrolysate with 9.93% lose in amino acids. Ginger, Giant Fennel and garlic could mask fishy odor, with better effect if heated. Using activated carbon to de-fishy odor resulted in 2.77% loss in amino acids, along with decolor of low-valued fish hydrolysate.The pH value of Low-valued fish hydrolysate was adjusted to 5.66 using NaOH. Tyrosine was deposited using following condtions: 0.1% EDTA, 5℃,10rpm stirred for 24h. Lysine, arginine and histidine was adsorped by 732 ion-exchanger resin and eluted using different concentration of ammonia liquor with yield of 58.65%,92.15% and 79.98%, respectively.