Effect of Pretreatment on the Peeling and Myofibrillar Protein of Pacific White Shrimps

In this study, the effects of different pretreatments (enzymatic treatment, freezing and soaking in ice-salt solution mixture) on the peeling of the Pacific white shrimp Penaeus vannamei and myofibrillar proteins in it were investigated. Shrimp peelability, the texture of peeled shrimps and the physicochemical and structural characteristics of myofibrillar proteins were analyzed after pretreatment. The results showed that compared with the two other pretreatments, enzymatic pretreatment for 3.5 h reduced the work required to peel shrimps and resulted in no significant difference in complete peeling rate (P > 0.05). The enzymatic treatment markedly decreased Ca²⁺-ATPase activity, the contents of total sulfhydryl and active sulfhydryl and intrinsic fluorescence intensity. The contents of total sulfhydryl and active sulfhydryl and intrinsic fluorescence intensity but not Ca²⁺-ATPase activity were decreased less by the enzymatic treatment than by freezing and ice-salt solution treatment. Enzymatically treated shrimps had no significant difference in surface hydrophobicity and protein carbonyl content compared with fresh and ice salt-treated samples, respectively (P > 0.05). Fourier transform infrared (FTIR)spectroscopic analysis showed that the contents of α-helix and β-turn in myofibrillar proteins were not significantly changed after pretreatment (P > 0.05), but the enzymatic and ice-salt treatments resulted in the transformation of β-sheet to random coil. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that freezing and ice-salt treatment changed the conformation but not the SDS-PAGE pattern of myofibrillar proteins. The enzymatic treatment caused the degradation of some macromolecular proteins, but did not cause a significant difference in the texture characteristics of shrimp meat compared with freezing and ice-salt treatment.