| Currently, there are less products of oysters in the market, such as raw, dried,retort pouch, oyster sauce, and functional products. The new rise of ultra high pressure processing technology(Ultra high pressure, UHP) in the static high pressure(greater than 100MPa) treatment under conditions for some time, causing food ingredients, non-covalent bond formation damage or make food proteins, enzymes,starch, and biopolymer materials were denatured, inactivation and pasting, while killing bacteria and other microorganisms in food, and thus achieve the purpose of sterilization of food preservation and processing. Thus, ultra high pressure processing technology is one of the most promising non-thermal processing technologies.In this paper, we firstly optimized the ultra high pressure sterilization process conditions from Crassostrea hongkongensis. Secondly, we studied the effect of ultra high pressure on the quality of oyster. Thirdly, we developed a ready-to eat UHP process oyster product and forecast the shelf life of the product. The main studied contents and conclusions were showed as follows:1.The study used Box-Behnken design to establish data set. With the total bacteria(lg(cfu/g)) as the reference standard, the neural network model simulated ultrahigh pressure sterilization of oyster was established with the help of JMP7.0software platform. The results showed that the best process condition was the pressure was 350 MPa for 20 min and the temperature was 30℃, the oyster meat total bacteria after pressure treatment in this condition decreased from 3.2718 to 2.44342lg(cfu/g)(The sterilization rate was 85.13%), and Coliforms decreased from 7 to 0(MPN/100g). The microbial indicators in line with Shellfish health standards, and little change on appearance and quality with the naked eye observation differ with fresh oysters. Validation test results showed that the established neural network model has better prediction ability which can accurately predict the sterilization effect, and the relative error of predicted values and experimental values is small(0.201%).2.Compared with fresh oysters, ultra high pressure on oyster quality have different degree of change, high pressure make the oyster moisture content increased by 2.47%, protein and ash content decreased by 1.48% and 0.76% respectively, crude fat and total sugar content, hydrolytic amino acids and fatty acids composition wasnot changed significantly. Compared with the heat treatment, ultra high pressure processing is more conducive to retain the oyster original nutrients.3.Compared with fresh oysters, UHP treatment can make the protein in slight degeneration, pH increased0.14, protease hydrolysis activity and Ca2+-ATP enzyme activity decreased by 34.26% and 7.81% respectively; Significant increase in hardness and chewiness of muscle, hardness, flexibility and chewiness of tissue significantly reduced; UHP treatment made L value increased significantly, a, b value are decreased significantly, and muscle color change is the most serious; While DSC and optical microscope and SEM results also showed that UHP treatment cause protein denaturation, and make the structure more closely. Compared with heat treatment, the oyster protein after heat treatment severe serious degeneration.4.Compared with fresh oysters, UHP make free amino acids and nucleotides and related compounds(except IMP) significantly, the amount of organic and inorganic ions decreased significantly, betaine did not change significantly. Changes in heat treatment is more obvious than changes in UHP treatment.5.Compared with fresh oysters, aldehydes, which is the odor of the biggest factors affecting oysters, is slightly increased, TBA value increased 50.30% also confirmed aldehydes have accumulated after UHP treatment, ketone is slightly decrease. But after heat treatment, the content of aldehydes and alcohols content increased by 22.92% and decreased by 22.56% respectively, so the heat treatment weakened oyster original fishy smell and strengthened meaty.6.Oysters during storage at 4 ℃, the moisture content of oyster after UHP treatment tended to decrease; pH value decreases after the first big change; The abdominal and back muscles a value, b value increases, that is yellow, green; Muscle chewiness increases, the hardness, springiness, chewiness of tissue were decrease trend. Changes in the control group was more significantly than the UHP group.7.Oyster meat in the cold storage treat total bacterial count as an indicator, build first-order kinetic model: SL=0.00127·exp(2673.5/T) can be predicted in the cryopreservation of oyster meat shelf life. treat total bacterial count as an indicator,the temperature is 0, 4, 8, 25℃, UHP processing oyster meat shelf life was 22 d, 19 d,17d and 10 d. |
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