Asian Journal of Microbiology, Biotechnology & Environmental Sciences Paper

QUALITY CHANGES IN FRESHWATER PRAWN MACROBRACHIUM MALCOLMSONII (H. MILNE EDWARDS) DURING STORAGE

S. SELVAKUMAR, V. BINDHUMOL AND P. GERALDINE

Abstract

Live prawns of Macrobrachium malcolmsonii procured from local fishermen were used for storage studies. The whole prawns were subjected to different storage conditions, such as in the crushed ice, in the frozen state at-20'C, and at room temperature (30±1C) for 48 hr. The changes in sensory, biochemical and bacteriological characteristics in the muscle of these prawns at the end of 48 hr were compared to those occurring in fresh prawns. A yellow-orange discoloration, with black spots in the region of overlapping shell segments, that was noticed in the M. malcolmsonii maintained at room temperature, was more intense than in prawns maintained in ice. The concentrations of total protein, carbohydrate and lipid were lower in muscle of prawns maintained in crushed ice and at room temperature than in fresh prawns; this was most pronounced in prawns stored at room temperature. However, there was essentially no difference in the concentration of these components between the muscle of prawns maintained in frozen and that in the fresh prawns. Qualitative analysis of muscle protein by SDS-PAGE revealed severe degradation in prawns maintained at room temperature, as evidenced by a reduction in the number and staining intensity of polypeptides. However, the patterns of major polypeptide bands were essentially similar in prawns maintained in ice, in the frozen state and in fresh prawns. Bacteriological studies indicated bacterial growth in the muscle of prawns kept at room temperature; the mean total viable bacterial count was found to be 2x103 cfu/g. No bacterial growth was evident in the muscle tissue of fresh prawns or in those that had been maintained frozen or in crushed ice. The results suggest that storage of prawns at room temperature may predispose to bacterial growth, ultimately leading to a deterioration in the quality of the prawn. Although icing curtails bacterial growth, a decline in muscle quality is evident within 48 hr, and this may be due to leaching. Hence, in order to ensure that there is no deterioration in the quality of the prawn even when stored for 48 hr, M. malcolmsonii should be kept frozen at -20°C.