Physical and biochemical changes in the moscle of giant fress water-prawn, Macrobrachium rosenbergii, during frozen storage and freeze-thaw cycles

Abstract

The effects of cold storage at 4°C, -18°C, and freeze-thaw cycles on the quality changes of prawn muscle were investigated. The biochemical changes during storage of 14 days were determined along with the techniques of light microscope and electron microscope. During the storage at 4°C for 14 days, the texture of prawn became softer and was not accepted after 6 days of storage. The softness of prawn may be due to the weakening of muscle structure resulted from hydrolytic enzymes degradation from prawn and microorganism. The Z-line distortion and l-band extension in myofibrillar proteins were observed. It was found that the solubility of actomyosin increased from 138.82 to 193.02 mg/g during 14 days of storage and changes of actomyosin pattern were observed when analyzed with SDS-PAGE. When prawns were stored at -18 °C, the texture became tougher with increasing time (O-6 months). It was found that the solubility of actomyosin was reduced from 150.50 to 121.90 mg/g during 6 months of storage. The amount of Ca2+ ATPase and the water holding capacity of proteins were also reduced. The changes of hydrolytic degradation products were found to be lower than the prawn stored at 4 °C. The changes in texture during frozen storage were probably due to the physical damage which resulted from the growing of the ice crystals size from 30.36 to 4O.87 μm in diameter and the increasing of the distance between muscle bundle from 9.61 to 13.96 μm during 0-6 months of storage. For the freeze-thaw of prawn muscle at 5 cycles, the changes in biochemical properties of protein were similar with the prawn storage at -18 “C for 6 months. However, the increase of the solubility of actomyosin, and the degree of myofibrillar protein deterioration were higher than the prawn stored at -18 °C, and furthermore, the texture of the prawn became softer as the freeze-thaw cycle of the prawn increased.