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The method of enzymatic hydrolysis was used to make fish protein hydrolysate by using scraps of low value freshwater fish, such as head, skin and bones as raw materials in this paper. Fishbone was immersed in organic acid, and the solution riched in organic acid calcium was prepared, which was added to the fish protein hydrolysate, then mixed and processed into fish protein hydrolysate related products that had high calcium content, rich nutrition and good flavor.The method of enzymatic hydrolysis was given to prepare protein hydrolysate for the low value freshwater fish in this article. As hydrolysis degree an index, enzymatic hydrolysis temperature, pH value, substrate concentration, add enzyme dosage, etc factors were investigated for the effect on hydrolysis degree of silver carp protein. The enzymatic hydrolysis temperature, pH value and enzyme dosage were optimized using central composite combination design test basis on the single-factor experiments, taken amino nitrogen as an index, the optimal enzymatic hydrolysis time was determined. The results showed that:the enzymatic hydrolysis pH9.37, temperature48.33℃, enzyme dosage93.87AU/kg, enzymatic hydrolysis time6h, protein concentration was3.62%. On this condition, the hydrolysis degree was39.54%, amino nitrogen content was2.30g/L, total nitrogen recovery rate was93.55%.Protein hydrolysate decoloring process using the method of active carbon absorption was investigated. As decolouring rate and nitrogen recovery indexes, different decoloring agents, active carbon dosage, pH value, temperature and time were researched for the effect on decoloring rate and nitrogen recovery of fish protein hydrolysate. The results showed the decoloring effect of silver carp protein hydrolysate using powdered active carbon was good, through single-factor and orthogonal test, the optimal decoloring technology was determined:activated carbon content1.5%, PH5.0, temperature50℃, time40min. Under these conditions, the decolored rate of powdered activated carbon for the silver carp protein hydrolysate was77.9%, the nitrogen recovery rate was82.3%.To the rest of fishbone after hydrolysis for silver carp as raw material, through cleaning, drying and smashing, the solution containing organic acid calcium was prepared using organic acids. As calcium extraction an index, the effect of factors such as acid selection, acid dosage, reaction time, temperature and substrate concentration for the extraction of organic acid calcium was investigated. By single-factors and orthogonal test, the best process conditions of extracting organic acid calcium were gained:choosing lactic acid as extracted acid, it was extracted for3h at temperature40℃, material liquid ratio1:30, lactic acid dosage29%, which organic acid calcium extraction rate was as high as75%.The research on nutrients and pHysicochemical properties of the fish protein powder showed that the fish powder made by enzymatic hydrolysis after vacuum freeze-drying was rich in protein which contained higher essential amino acid and had very good nutritional value. Product has good solubility and its solubility are over95%at the range of pH2.0to10.0, low viscosity that will not affect on food fluid properties, and has good foaming ability and foam stability. Therefore, it can be used widely as a protein fortifier to the food industry and it has a good application prospect.Taken protein powder made by enzymatic hydrolysis for low value freshwater fish as base makings, using the orthogonal experiment design, the optimal seasoning formula of low value freshwater fish was obtained that:ginger and garlic powder1%, low value freshwater fish protein powder10%, salt20%, sugar6%. By sensory evaluation, low value freshwater fish condiment has natural, pure fish smell, delicious taste and nutritional value.
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