| Whitefish(Topmouth culter)is rich in nutrition, containing a variety of minerals and other nutrients. With the tender and not greasy texture, it is in the top grade of fish. Taihu whitefish is known as one of the "three treasures of Taihu Lake", along with Taihu whitefish and white shrimp. Because the muscle is very easy to spoilage, whitefishes are mainly consumed freshly, resulting in the limited marketing area. At present, processing products for whitefish is mainly focused on the traditional air-dried whitefish with high salt content and low moisture content, which lose original delicious flavor. Up to date, there is no research reports about the manufacturing of semi-dry and low-salt fish products, the aim of this paper is to carry out the study on microbial, lipid oxidation and endogenous enzyme control during the processing of whitefish, in order to develop a whitefish product with high water content, low water activity, long shelf life, and the natural flavor to satisfy the market demand. The main research results and conclusions are given as follows:(1) 11 bacteria were isolated from the naturally corrupted whitefish, including Morganella sp.S-1,Morganella sp.S-2, Proteus sp.S-3, Proteus sp.S-4, Proteus sp.S-5, Vitreoscilla sp.S-6; Vagococcus sp. S-7, Vagococcus sp.S-8; Terribacillus sp.S-9, lysinibacillus sp.S-10; Staphylococcus sp.S-11.(2) The inhibitory effect of antimicrobial agents in pH 4adjusted by acetic acid was significantly greater than that in lactic acid(P < 0.05). Among all antibacterial agents, butyl paraben showed inhibitory effect on all tested spoilage bacteria, wih the widest antibacterical spectrum and the most greatest antibacterial activity. The optimal inhibitory formula is 5.00%garlic,0.05%butyl paraben and pH=4.4.(3) The effect of different pH, temperature, salt content, rice wine, enzyme inhibitor on endogenous enzyme activity were studied.pH4.5,departuring the optimum pH, for endogenous enzyme, had a good protective effect on the degradation of myofibrillar protein. Residual activity of cathepsin B, L and calpain at 20℃ were the lowest,and myosin heavy chain were not degrade, residual activity of cathepsin B, L, D with the addition of 0.75% salt were 41.02%,41.76%,49.08%respectively,significantly lower than those with lower salt concentration(P < 0.05).Five-year-old rice wine had greater inhibitory activity against,cathepsin B, L, D and calpain than other types of rice wine,with the residual enzyme activity of 43.12%, 44.20%, 43.11%, 4.66% respectively.With the concentration of 1%, inhibitor 1 inhibited the degradation of myosin heavy chain. The optimal conditions for the inhibition of endogenous enzymes were: pH=4.5, 20℃,0.75% salt additions, Five-year-old rice wine, and 1% inhibitor 1.(4) 4% propylene glycol effectively could reduce water activity in whitefish to 0.746. It could also significantly reduce the content of MDA and the lipase activity.(5) Through Placket-Burman experiment, BHT and tea polyphenol were chosen as effective antioxidants(P<0.05).At 40℃ in light for 24 h,the inhibition against lipase of 0.15% tea polyphenol combined with 0.05% citric acid and BHT were 46.00% and 9.29%, while inhibition efficiency against lipoxygenase 85.90% and 43.04%. The inhibition on MDA and POV was 59.03% and 32.78% respectively. The synergic effect of tea polyphenols and citric was better than that of BHT.(6)6 types of different whitefishes were prepared using different methods. After the 8 days of storage at 30℃,sample 2 has the moisture content of 38.80%,water activity of 0.833,aerobic bacterial count of 3.97 Log CFU/g, TVB-N of 25.2mg/100 g,MDA content of 1.48mgMDA/g, putrescine of 350.75μg/g and histamine of 116.78μg/g, as well as the lower lipase and lipoxygenase activity compared to other samples. Whitefish sample 2 had the best sensory quality with firm and elastic texture, fresh and enjoyable odor, and moderate salty taste. The formula and method established in this paper could be successfully used for the factory production of the whitefish. |
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