Effects Of Dense Phase Carbon Dioxide On Pasteurization, Enzyme Inactivation And Quality Of Litopenaeus Vannamei

Dense phase carbon dioxide （DPCD） is a non-thermal pasteurization method thataffects microorganisms and enzymes through molecular effects of CO₂underpressures below50MPa and temperature below60℃. DPCD process is operatedunder moderate conditions with energy conservation. CO₂is inexpensive, non-toxic,non-flammable, and physiologically safe, with a low critical temperature. Therefore,DPCD sterilization technique could be one of the most promising techniques withoutexposing foods to adverse effects of heat and retaining their freshlike physical,nutritional, and sensory qualities.In the paper, the effects on microorganisms, polyphenol oxidase （PPO） andquality of Litopenaeus vannamei by DPCD treatment were investigated in order toexplore the feasibility of shrimp by DPCD process. The results were as follows:The inactivation of polyphenol oxidase （PPO） from Litopenaeus vannameiexposed to DPCD treatment was investigated. PPO activity showed a dramatic lossat4-25MPa and37℃. At the lower pressure （4-15MPa）, the experimental data ofinactivation followed the first-order reaction kinetic model. At the higher pressure（20and25MPa）, the experimental data of inactivation followed to biexponentialkinetic model. After DPCD treatment, the loss activity of PPO had no restorationstoring for6days at4℃. The results of SDS-PAGE and activity staining alsoshowed that DPCD treatment had the obvious inhibitory effect on PPO. The PPOactivity in vivo was easier to be inactivated than that in crude PPO extracts under thesame DPCD treatment conditions.Aerobic plate counts inactivation of Litopenaeus vannamei by dense phasecarbon dioxide （DPCD） treatment was investigated and neural network was used tooptimize the process parameters of microbial inactivation. A3×5×2three-layerneural network model was established. Moderate temperature55℃with15MPa for26min treatment time achieved a3.5-log reduction of total aerobic plate counts （TPC）, namely the residual bacterial count in shrimp was less than300CFU/g,which achieved desired level of microbial inactivation required by hygienicrequiremnet for cooked aquntic products.DPCD treatment had a remarkable bactericidal effect on Chryseobacterium sp.LV1, the inactivation effect was enhanced with pressure, temperature and exposuretime increasing. Supercritical CO₂was more effective in inactivating microbial cellsthan CO₂under subcritical conditions. DPCD induced leakage loss of the proteinsand DNA of Chryseobacterium sp. LV1. With regard to the proteins, the resultsshowed that a substantial amount of the total soluble proteins had converted intoinsoluble protein. In addition, DPCD selectively inactivated bacterial enzymes ofChryseobacterium sp. LV1, alkaline phosphatase was not affected by DPCDtreatment.DPCD treatment could retain their nutritional quality, there were no significantdifference （p>0.05） of the protein content between untreated and DPCD treatedshrimp. The appearance of Litopenaeus vannamei was nearly same to that treated byboiling water. DPCD could lead to cooking loss of shrimp muscle, but pH of shrimpmuscle was not changed. Protein denaturation was observed by DPCD treatment, thewater hold capacity （WHC） of shrimp muscle significantly decreased. There were nosignificant difference （p>0.05） of shrimp muscle hardness between untreated andDPCD treated shrimp. However, the spring of shrimp muscle significantly decreased.Of the taste-active components in the muscle of shrimp, no significant differenceswere found in taste-active components except betaine, PO43-and Cl-between DPCDtreated and untreated shrimp. With regard to the traditional cooking method ofboiling water, however, the treatment leaded to significantly loss of the taste-activecomponents in shrimp muscle.The results showed that DPCD could inactivate the PPO activity andmicroorganism of Litopenaeus vannamei. Compare with the traditional cookingmethod in boiling water, DPCD treatment could retain the nutritional qualities ofLitopenaeus vannamei and have little effect on taste-active components. Therefore,it’s feasible for shrimp processing by DPCD treatment. The results also providesome information for DPCD treatment in the application of aquatic products.