Study On The Preservation Of White Shrimp (Litopenaeus Vannamei) Under Controlled Freezing-point Storage And Modified Atmosphere Packaging

Based on the disadvantage of fresh-keeping logistics, in the paper, the main problems including quick drop of the freshness, short shelf life and small radius of logistics system were investigated. The final object of the study was to provide the theory and essential technique for the preservation and modified atmosphere packaging system of white shrimp (Litopenaeus vannamei) under controlled freezing-point storage.This study includes five parts of content as follows:1. Evaluation on quality of white shrimp (Litopenaeus vannamei) under controlled freezing-point storageNutritional components and descriptive analysis were integrated to investigate quality changes of white shrimp samples by the way of secondary instrumental measurement and biochemical analysis methods under controlled freezing-point storage, then the shrimp quality determination system was set up by factor analysis and distances correlation analysis of data. Results indicated that there were significant difference(P<0.05) in the nutritional components, trained panel assessment, texture, color and biochemical measurement, respectively. Moreover, nine factors were obtained by distances correlation analysis, it was concluded that most of factors, such as nutrition components factor, color factor, biochemical factor and so on, had significant correlations(P<0.05), whereas indistinctive correlations were found among descriptive factor, texture factor and color factor(P>0.05). Consequently, descriptive analysis could not replace the instrumental measurement methods. On the contrary, the three ones should be integrated to reflect the changes of quality in white shrimp (Litopenaeus vannamei) during controlled freezing-point storage.2. Thermophysical properties evolution of white shrimp (Litopenaeus vannamei) meat during phase transitionIn order to provide available thermophysical property parameters and obtain optimum freezing-point regulators for fresh-keeping of marine shrimp, initial freezing point(Tf), the unfreezable water mass fraction(a), apparent specific heat(Capp), enthalpy(H) of white shrimp (Litopenaeus vannamei) and effects of GLY, NaCl and Sorbitol content on thermophysical properties of white shrimp (Litopenaeus vannamei) during phase transition were studied by differential scanning calorimetry (DSC) and D-saturated optimum design. Results indicated that the effect of compound regulators on four response factors(Tf, a, Capp and H) was as follows:Tf, Sorbitol>GLY>NaCl(P < 0.01);α,GLY>NaCl(P<0.01)>Sorbitol(P<0.05); Capp, NaCl(P<0.01)>GLY >Sorbitol (P<0.05); H, GLY>NaCl>Sorbitol(P<0.01). As the content of compound regulators increased, the thawing phase transition range of white shrimp meat shifted to the lower temperature range, and the content,of unfreezable water increased, while the initial freezing point decreased linearly, and both of latent heat and the peak value of apparent specific heat decreased. The initial freezing point, the content of unfreezable water, the latent heat and the peak value of apparent specific heat were-17.4402℃,17.2223%,41.0379J/g and 155.9419J/(g℃) under the ratio of 0.8.761% for GLY,2.2938% for NaCl and 0.5887% for Sorbitol, respectively.3. Study on the optimized modified atmosphere for packaging of white shrimp (Litopenaeus vannamei) by mixture designThe optimal initial gas composition to maintain quality of modified atmosphere (MA) packaged white shrimp (Litopenaeus vannamei) under controlled freezing-point storage was determined through microbiological analyses, sensory evaluation of raw odour and appearance, exudates, pH and TVB-N analyses. White shrimp packaged under gas to product ratio of 3:1 and gas mixtures according to a simplex centroid mixture design spanning the whole area from 0 to 100mL/100mL and in between mixes of all the three major packaging gases, CO2, O2 and N2 were analysed after 2,4 and 6 days of storage, moreover the correlation among all variables was analyzed by partial least squares (PLS-2) regression. Mesophilic and psychrotrophic plate count decreased and amount of exudates increased with increasing CO2 concentration, while mesophilic, psychrotrophic plate count and values of total volatile basic nitrogen (TVB-N) increased with elevating N2 levels. Odour and appearance decreased in the white shrimp with decreasing CO2 and O2 levels. However, high O2 concentration could accelerate the browning of white shrimp. On the contrary, suitable O2 was beneficial to maintain the odour of white shrimp. The weighted optimum gas mixture for MA packaging of white shrimp was determined to be 74.2mL/100mL CO2,9.7 mL/100mL O2 and 16.1mL/100mL N2.4. Effects of various packaging conditions on microbiological, biochemical and sensory attributes of white shrimp (Litopenaeus vannamei) during controlled freezing-point storageEffects of vacuum and modified atmosphere packaging (MAP) on bacterial flora, pH, total volatile basic nitrogen (TVB-N), exudates and sensory attributes in white shrimp (Litopenaeus vannamei) during controlled freezing-point storage were investigated. The results indicated vacuum, MAP1 (40%CO2/30%O2/30%N2) and MAP2 (75%CO2/10%O2/15%N2) samples were more effective for inhibiting growth of total mesophilic bacteria, Aeromonas spp. and psychrotrophic bacteria compared to air package (AP) (P<0.05). During the storage period, Pseudomonas spp. dominated final spoilage organisms of white shrimp in AP, VP and MAP1, and Lactic acid bacteria (LAB) and Enterobacteriaceae became also dominated spoilage organisms stored under VP and MAP2, respectively. The pH value of various packaging samples showed the similar changes during storage. However, pH values of AP samples were significantly (P<0.05) higher than those of VP and MAP package. The TVB-N content of the samples stored under AP exceeded the upper threshold of 30mg N/100g shrimp muscle on the 5th day after storage. VP, MAP1 and MAP2 treatment significantly inhibited the increase of TVB-N (P<0.05). Formation of exudates (EX) under AP, VP, MAP1 and MAP2 increased during the storage, and the value was higher with the increase of CO2 levels in the packaging (MAP1 and MAP2). Sensory analyses (odor and appearance attributes) indicated that a shelf-life of ca.4 days for AP,7 days for VP, 9 days for MAP1 and 11-12 days for the optimum MA-packaged white shrimp samples stored at controlled freezing-point temperature, respectively.5. Study on the preliminary screening and optimization of inhibitors for white shrimp (Litopenaeus vannamei)Based on the preliminary screening of inhibitors and bacteriostatic ring, the optimal proportion of inhibitors to prolong the shelf life of white shrimp (Litopenaeus vannamei) under controlled freezing-point storage was determined through microbiological analyses. Microbiological changes of white shrimp in the putrefactive time and different proportion of inhibitors according to a quadratic general rotary design were analyzed. Results demonstrated that tea polyphenol (TP), nisin(NI), chitosan(CHI) and lysozyme(LY) could notably inhibited the growth of spoilage organisms, Furthermore, TP and CHI had significant inhibition on Pseudomonas spp., Aeromonas spp., Lactic acid bacteria and Enterobacteriaceae, while LY and NI had no effect on other spoilage organisms but Lactic acid bacteria. Secondary relationship under three factors (X1—TP, X2—CHI, X3—NI) quadratic general rotary design was figured to be Y=97.59591-11.05664X1-16.78799X2-7.22909X3-4.69267X12-6.46044X22-3.63201X32+4.12500X1X2+3.37500X1X3+3.87500X2X3,There were obvious interactions between X1 and X2, X2 and X3 (P<0.05), but no obvious interactions between X1 and X3(P>0.05). The effect on inhibiting microbiology was X2>X1>X3. By means of frequency response analysis, the optimal proportion of inhibitors was determined to be 0.30g/L for X1, 1.00g/L for X2 and 0.60g/L for X3.