Dried Fish Process Optimization And Its Quality Changes In The Course Of Processing

Seawater fish is rich in protein, vitamins and trace elements and it is one of the important sources of nutrients. There are a variety of products in the fish processing, but the current commercially available dried fish products have the high salt content, hard texture, flavor deficiencies of defects though they have a long shelf life. For developing low salt, good taste and rich flavor of fish products, we chose puffers as experimental material at first. Using eight kinds of process scheme to process the puffer fish, then we studied the sensory characteristics of the product, regularity of moisture migration in the dried process and the changes of proteolysis index, amino acids, fatty acids and flavor components. Through the studies above, we obtained the best dried processing technology of puffer fish. Then we selected the optimum processing technic to process other fishes (hairtail, leading fish, Basa, etc.), and to study the quality changes. At the finally, using sardines as the research object, the quality changes of marine dried fish processed by the ultra high pressure, PAP and the high temperature and high pressure sterilization methods were explored. The research results are as follows:1. Using puffer fish as the research object, we designed eight different pickling, seasoning and drying process. Program 1:70±2? high temperature dried after curing, then added seasoning oil; scheme 2-5: two cured formula, dried at 45±2?, added different seasoning oil respectively; scheme 6-8:three cured formula, dried at 17-29?, relative humidity was 60%-80%. The puffer fish dry sensory evaluation was carried out. The results showed that the sensory scores of dried products at the low temperature and medium temperature were significantly better than that dried at high temperature.2. The puffer fishes were processed with two kinds of curing formula, respectively. We used two kinds of temperature (scheme 1 and 2 as the temperature in the medium drying,3 and 4 for the scheme of low temperature drying), with water activity fell to 0.88 in which the experimental effect was best. The nutritional composition, TVB-N value, TBARS value, water dynamic changes and final product flavor components were determined and the test results showed that:(1) with the course of processing, the moisture content and water activity decreased gradually, the content of protein and ash increased. Due to the seasoning oil added in the product processing, the fat content significantly increased; (2) TVB-N value increased gradually in the course of process and TVB-N value in dried puffer product reached 70 mg/100 g. There were no significant differences among the four schemes; (3) TBARS value showed increasing at first and then decreasing and reached 2.4-2.9 mg/kg at the end; (4) water both inside and outside in scheme 3 and 4 distributed uniformly and could achieve good drying effect than scheme 1 and 2; (5) the kinds and contents of flavor components processed at low-temperature drying were higher than those in medium temperature conditions, indicated that the low temperature drying process is more conducive to the formation of flavor substances; (6) two curing formula had no significant effect on nutrients, TVB-N and TBARS and water migration of died puffer fish, but the relative types and contents of flavor components had some different. Through the above results, we concluded that puffer dry product quality processed in low temperature was relatively higher.3. In this part, we selected puffer fish processed in low temperature drying and studied the changes of proteolysis indices, free amino acid, fatty acid and flavor indexes. The results showed that with the air drying process, the protein hydrolysis index, free amino acid content and fatty acid content of puffer fish were significantly increased (P< 0.05). Comparison of the two dried puffer fish with different curing processing formula, we found that proteolysis index, amino acid and fatty acid types were not obvious. Some amino acid and fatty acid content had significant differences and this lead to the flavor differences. The volatile compounds in dried puffer fish mainly were alcohols, aldehydes, ketones, esters, hydrocarbons. Other substances, such as sulfur compounds and furan compounds, the relative content was low.4. Puffer fish processing technology (low temperature drying under the two curing scheme) was also applied to improve the taste and flavor of other fishes (Harpodon nehereus, Basa, Trichiurus haumela). Due to various volatile substances in different kinds of fishes, the flavor substance contents of the three fishes had significant differences. The flavor of dried sea fish was significantly improved compared to fresh sea fish. There are some differences between the kinds and contents of flavor substances produced after air drying because effects of their volatile precursors produced by different kinds of fish.5. Using the optimum conditions above to process dried sardines, at the end of drying, we packed the products in a vacuum. Then we conducted the heat preservation storage (37 ?) experiments by ultra high pressure sterilization (300 MPa,30 min), pasteurized (in the bath after a rapid cooling sterilization for 30 min, followed by 30 min of sterilization), high temperature and high pressure sterilization (121 DEG C,20 min). At the same time, the fishes no sterilization was adopted as blank control. The results showed that: (1)During the storage process, order of TVB-N value(from low to high), TBARS value(from low to high) and Sensory evaluation (from high to low) in 4 groups of sardines fish at the same time was high temperature and high pressure group, high pressure group, pasteurization group, blank group. (2)the total number of microorganisms (CFU/g) was used as the standard to evaluate the microbial shelf life of air dried. Microbial shelf life of each group was:blank group(36 d), high pressure group(45d), pasteurization group(52d), high temperature and high pressure group(60d). In conclusion, high temperature and high pressure is a good disinfectant from the economic and shelf life considerations, pasteurization is suitable for use in the direction of the development of meat products.