Application Of Super-chilling, Modified Atmosphere Packaging And Fresh-keeping Agents On Preservation Of Pacific White Shrimp

In order to inhibit melanosis of Pacific white shrimp(Litopenaeus vannamei) and prolong their shelf-life, Pacific white shrimp(Litopenaeus vannamei)cultivated in Nanhui District, Shanghai were selected and they were treated respectively with super-chilling, modified atmosphere packaging, preservative and differet combinations of these methods. Polyphenol oxidase (PPO) activity, sensory evaluation,total bacterial count and other physical indexs were determined to evaluate the effects of the different preservation methods on shrimps. The research datas can provide some theoretical and technical support for processing of pacific white shrimp. The results were gotten as follows:1,Effects of super-chilling on preservation of pacific white Shrimp were studied. Based on the freezing experiments, the ice point of Pacific white shrimp was -2.2℃, Magnitude of changes of sensory evaluation score, PPO actives, melanosis, TVB-N, pH, TBC of the treated were rather less than those of the controlled. The shelf-life of the treatment was 8 days, while the shelf-life of the controlled was only 4 days. The super-chilling technolgy which was a safe physical preservation method with out preservative which can prolong the shelf-life and delay the quality losses of Pacific white shrimp obciously, It was valuable to extensively popularize the super-chilling method on preservation of Pacific White Shrimp in the light of its safeties and effects.2,The techniques and freshness keeping effect of modified atmosphere packaging (MAP) of the different combinations proportion of CO₂, O₂ and N₂ on Pacific white shrimp were studied. Shrimps were modified atmosphere packaged with the K-PET/PE bags of the high-barrier compound packaging materials, then all groups were preserved at 4℃. The sensory evaluation, L* value, b* value, pH, total bacterial count (TBC) and total volatile basic nitrogen (TVB-N) were examined to assess freshness-keeping effects of all groups. The results showed that the freshness keeping effects of 85% CO₂/5% O₂/10% N₂ and 40% CO₂/30% O₂/30% N₂ were the best of all, they obviously extended the shelf-life of Pacific white shrimp at the cold storage to 12 days.3,Melanosis inhibition of 0.002% 4-HR with 1% chitosan (Group A), 0.01% 4-HR with 1% chitosan (Group B) and 0.05% 4-HR with 1% chitosan (Group C) on Pacific white shrimp were examined under cold store. The changes of sensory evaluation of melanosi(sMSE), polyphenol oxidase (PPO), total bacterial count (TBC) and total volatile basic nitrogen (TVB-N) of shrimp were determined, the residual levels of 4-hexylresorcinol(RLOHR)was also detected. The results showed that the values of PPO and MSE of Group C were the lowest compared with the others throughout the storage process, but the RLOHR of Group C had exceeded 1 mg / kg on on the 4^th day, The PPO and MSE of Group A and Group B were no significant difference (P>0.05) on the 4^th day, but the time of RLOHR of two groups exceeded 1 mg / kg was the 4^th and 6^th day, respectively. According to TBC and TVB-N values, the shelf life of A, B and C were 6 days, 6 days and 8 days, respectively. The shelf life of the controlled was only 4 days. A certain concentration of 4-HR combined with chitosan can not only delay the melanosis safely and effectively, but also extend the shelf-life.4,Effects of super-chilling combined with preservatives on melanosis and qualities of Pacific white shrimps were examed. The results showed that the temperature of super-chilling ranged from 0 to -2.2℃, and the temperature fluctuation of a common refrigerator met the requirements of super-chilling. The formulation was optimized using orthogonal array design. A blend containing 0.01% 4-hexylresorcinol, 1.5% citric acid and 1% ascorbic acid provided an optimal inhibitory effect against the darkening of Pacific white shrimps and could effectively inactivate PPO activity. Super-chilling could make the growth of TVBN,pH and TBC slow down significantly. The combination of super-chilling with the optimized blend gave a mutual complement between them, presented a more significant inhibitory effect against the darkening of Pacific white shrimps and the growth of PPO activity, TVB-N, pH and TBC, and resulted in a 2-fold prolongation of shelf-life when compared with cold storage at (4±1)℃. These results showed that super-chilling provides a promising technique for delaying the darkening and prolonging the shelf-life of Pacific white shrimp.5,Effects of film-forming combined with modified atmosphere packaging on qualities of Pacific white shrimp were studied. 1% chitosan was combined with a kind of mixed anti-melanosis component (M) to prevent corrosion of Pacific white shrimp under modified atmosphere packaging (MAP) of two gas mixtures (40% CO₂ /30% O₂ /30% N₂ (Ⅰ) and 85% CO₂ /5% O₂ /10% N₂ (Ⅱ) )with high-barrier packaging bag (K-PET/PE) at (4±1)℃. The mixed anti-melanosis component (M) were optimized by orthogonal experiment, the optimal combination was as follows, 0.01% 4-hexylresorcinol+1.5% citric acid+1% ascorbic acid, the Group (Chitosan+Ⅰ), (Chitosan+M+Ⅰ), (Chitosan+Ⅱ) and (Chitosan+M+Ⅱ) began to generate melanosis dramatically at 6th, 8th, 12th and 14th day, respectively; all treatment groups, compared with the control, could slow down the increase of TBC, TVB-N, PPO activity and the pH significantly during the whole storage period. The fresh-keeping effect of Group (Chitosan + M +Ⅱ) was the best in all groups, extending the shelf-life of Pacific white shrimp more than two times compared with that of the control when stored at (4±1)℃. Film-forming combined with modified atmosphere packaging is an effective preservation method for Pacific white shrimp, which has application values.6,The effects of modified atmosphere packaging (MPA) combined with Super-chilling on pacific white shrimp were studied. The shrimps were treated with modified atmosphere packaged (85%CO₂/5%O₂/10% N₂) and were preserved at the super-chilling temperature (confirmed by the freezing experiment and temperature fluctuation of refrigerator). The shelf-life of the control, the group MAP, the group super-chilling and the group MAP plus super-chilling was respectively 4days, 8days, 12days and 16days.MAP and super-chilling have a extraordinarily collaborative effects, MAP plus super-chilling can strikingly delay the melanosis and extend shelf-life of Pacific White Shrimp.