Postharvest management and spoilage of tropical shrimps (Penaeus notialis)

Abstract

Traditional shrimp processing sites and marketing centres were surveyed to evaluate the effectiveness of traditional methods of processing and storage. Smoking and sun-drying were found to be the only methods used in shrimp processing in Ghana. The most common marine shrimp species, Penaeus notialis, was smoked in traditional ovens using mainly Paspalum vaginatum, Aristida sp. and Philoxerus vermicularis plants which impart an orange glossy colour to the smoked shrimps. Drying involved spreading the shrimps in the open sun on mats, sea sand or bare ground. Improper and unhygienic management (including personal body cleanliness, unclean equipment and environment), handling, storage and marketing procedures were found to lead to massive economic and financial loss to the processors and retailers alike as a result of high levels of contamination of the shrimps. A beetle, Dermestes frischii and its larvae were found to infest the shrimps in large numbers resulting in considerable quantitative and qualitative losses. Packaging is done by loading the fish in sacks and paper-lined baskets in large quantities such that stacking during transportation leads to fragmentation and spoilage. Micro-organisms isolated in processed shrimps include Enterobacter, Aeromonas, Pseudomonas, Acinetobacter, Micrococcus, Corynebacterium, Bacillus, Monilia, Aspergillus and Mucor. However, no pathogen of public health significance was isolated. Quantitative aerobic bacterial load recorded for fresh shrimps was high (2.4x 10⁸ bact/g). For the sundried and smoked marine samples, counts were comparatively low. Smoked lagoon samples recorded 7.8x I0⁴ org/g. Negligible levels of mould and yeast counts were recorded especially for the smoked marine shrimps (<10 cfu/g) while sun-dried marine and smoked lagoon shrimps recorded 1.4xl0¹ and 1.8xlO¹ cfu/g respectively. With storage, bacterial count increased to between 8.7xl0³ and 2.4x10⁵ org/g for market samples as compared to negligible increase in values of samples stored in the laboratory over 4 month period. Mould count for market samples also increased to between 2.3x 10¹ and 4.6x 10³ cfu/g over the same period. Increase in microbial count correlated with decrease in sensory quality. Moisture content of marine smoked and sun-dried shrimps ranged from 14-18%, protein 50-58.7%, fat 2.4-4.1%, free fatty acid (FFA) content 22-43% (as oleic), with sun-dried samples having higher FFA content than smoked samples. Smoked lagoon shrimps from markets had moisture content of 14%, protein 68%, fat 3%, FFA 22% (as oleic) while those from processing sites had moisture 17.6%, protein 57.6% and fat 4.6%. The process of sun-drying exposed shrimps more to deterioration due to oxidation, with resultant increase in FFA than the smoking process