| Ultra high pressure is a novel non-thermal processing technology, which could notonly inactivate microorganisms and enzymes effectively and ensure food safety, but alsomaintain maximally food nutrition, color, aroma and taste, as well as improve texture andfunctional properties of food. Litopenaeus vannamei is one of the important aquacultureproducts in our country and is extremely popular with customers because it’s high nutritionalvalues and delicious taste. Shrimp with high moisture content easily cause qualitydeterioration and even spoilage under the action of micro-organisms and enzymes. In the paper,we firstly analyzed the tissue distribution of polyphenol oxidase (PPO) from Litopenaeusvannamei and the relationship between the PPO activity and shrimp melanosis duringstorage period. Secondly, we studied the effect of ultra high pressure on PPO activity andmuscle quality of shrimp. Thirdly, we developed a ready-to-eat peeled shrimp product withgood flavor. The main studied contents and conclusions were showed as follows:(1) Tissue distribution and PPO activity from Litopenaeus vannamei, the effects ofpackage (vacuum or non-vacuum) and storage temperature (-18℃,4℃,25℃) onmelanosis and PPO activity, the relations between shrimp melanosis and PPO activity andstorage temperature, were discussed. The results showed that the content and activity ofPPO from the carapace and head of shrimp was higher, while the content and activity ofPPO from the abdomen muscle and pleopods was lower. The optimal pH value of PPO was6and PPO was more stable and higher activity at pH6~8value. Shrimp melanosis waspositively correlated with storage temperature and catalytic reaction rate of PPO, while therelative activity of PPO was negatively correlated with storage temperature.Vacuum package and lower temperature storage can effectively inhibit shrimp melanosis.(2) As heat treatment for the control, the effects on ultra high pressure on shrimp PPOactivity was studied and the kinetic models of PPO inactivated by ultra high pressure wereestablished. The results showed that PPO activity was significant decreased (p<0.05) withthe increasing temperature by heat treatment. For ultra high pressure treatment, PPO wasactivated when the pressure was lower than300MPa, PPO activity maximally increased by57.61%; when the pressure was above300MPa, PPO activity decreased significantly(p<0.05). PPO was completely inactivated at500MPa for2min. Inactivation of PPO by heat treatment (60~100℃) and ultra high pressure (400~600MPa) followed the first-orderreaction kinetics. Under the same temperature conditions, Ultra high pressure couldeffectively inactivate the crude PPO extracts, but PPO was activated directly treated inshrimp vivo. Therefore, if PPO in shrimp vivo was completely inactivated, higher pressurewould be needed or the pressure would be combined with other cofactors for processing.(3) The effects of ultra high pressure on the muscle qualities (color, water-holdingcapability, protein composition, thermodynamic properties and microstructure, et.) ofpeeled shrimp were investigated. The results showed that ultra high pressure could makeshrimp with boiled flavor. With the increasing pressure at the same exposure time, the L*value, hardness and pH value of peeled shrimp increased significantly (p<0.05), thecontent of sarcoplasmic protein and myofibrillar protein decreased significantly (p<0.05),but weight loss, moisture content and a*value (p>0.05) did not change significantly(p>0.05). With the extending exposure time at the same pressure, the L*value, pH value,weight loss and hardness of peeled shrimp increased significantly (p<0.05), the content ofsarcoplasmic protein and myofibrillar protein decreased significantly (p<0.05), butmoisture content and a*value did not change significantly (p>0.05). Reduction andnon-reduction electrophoresis and DSC indicated that high pressure induced denaturationof protein. When the peeled shrimp was treated by300~500MPa, muscle fibers becomemore compacted, the bright and dark stripes of myofibril were damaged, broken orcollapsed, and surface morphology of muscle fibers became spongy by optical microscopyand electron microscopy.(4) According to the current market situation and the trends of shrimp products, aready-to-eat peeled shrimp was developed by ultra high pressure sterilization treatment anddetermined the shelf life by storage test. The results showed that the peeled shrimp wasmarinated in the flavor seasoning for3h at the room temperature, and then heated for120sby microwave (640W). Peeled shrimp was packaged by vacuum and sterilized by ultrahigh pressure at500MPa for10min. Peeled shrimp could be stored for about50d at4℃.The peeled shrimp product was in accordance with the food safety and hygiene standards.The retail price of ready-to-eat peeled shrimp is between5.69and7.39per bag. |
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