Abstract
This study has been carried out to determine the post-harvest quality changes in two main important crustaceans species (Macrobrachium rosenbergii and Penaeus monodon) of Bangladesh during low temperature preservation. A detailed information on post-harvest handling, transportation, storage, distribution and marketing chains of shrimp using a pre-tested questionnaire was collected from some selected shrimp farms, landing points, receiving centers/depots and shrimp industries of Khulna and Cox's Bazar area through interviews with a number of cross section of people. The volume of post-harvest losses as reported was in the range of 5-8% in traditinal farms of Khulna area. On the other hand, the volume of post-harvest losses was estimated around 5% in improved traditional farms of same locations in the shrimp depots of the region. The volume of post-harvest losses ranged from 1-14%, due to lack of sufficient ice, improper handling and lack of suitable transport facilities. Studies on the quality changes in freshwater prawn (M. rosenbergii) and brackishwater tiger shrimp (P. monodon) indicated that the shelf-life of freshwater prawn was 5-6 days in ice, while tiger shrimp for 8-9 days. Expressible moisture increased and the breaking strength of muscle decreased in both samples during storage. The muscle pH and TVB-N increased considerably during storage, while there was a large fall of Ca2+-ATPase activity in both samples during 10 days of ice storage. Upon proximate composition analysis, moisture and protein contents decreased in both samples but there has been little or no changes in lipid and ash contents during 10 days of ice storage. Some changes occur in protein fraction in M.rosenbergii and P.monodon samples where sarcoplasmic protein fraction decreased considerably in both samples but there was little or no changes occurred in myofibrillar and alkali soluble protein during 10 days of ice storage. Aerobic plate count (APC) in both samples increased during the ice storage but coliform count decreased or eliminated/absent at the end of the storage period. During ice storage Coryneforms and Bacillus were always dominant in M.rosenbergii, while Micrococcus and Achromobacter were dominat in P. monodon. The delay of icing of M. rosenbergii for 4,8 and 12 hr shortened the shelf-life 3, 2 and 1 day respectively, while delay in icing of P. monodon during the same periods shortened the shelf-life to 7, 6 and 5 days, respectively. Muscle pH, TVB-N value, peroxide value and APC increased rapidly, while ATPase activity and solubility decreased considerably in both samples delayed prior to icing. Shrimp samples iced at 4,8 and 12 hr delay dominated mostly by Micrococcus with 60%, 57.14% and 46.66%, respectively. Vibrio and Enterobacteriaceae in the samples of M.rosenbergii were not detected in the initial sample but they were detected in some samples during subsequent storage. Remaining myofibrillar ATPase activities of M. rosenbergii and P. monodon declined during 120 days of frozen storage at -20°C. The influence of pH on the changes in isolated myofibrillar ATPase activities for both the species after storage at -20°C for 2 days, 0°C for 2 days and 35°C for 30 minutes showed that both Ca2+-and Mg2+-ATPase activities were lower in acidic and alkaline pH regions and the activity remains relatively high at neutral pH regions. The study on the solubility under various pH during ice and frozen storage also indicated the higher solubility at neutral pH region and poor solubility at acidic and alkaline pH region. The inactivation rate constant (Kd) value for both species was also lower in neutral pH region while the rate was quite high at acidic and alkaline pH region at incubation temperature of 30° and 35°C respectively.