Comparative studies on the effect of gamma irradiation on decontamination and nutrient quality of smoked dry shrimp from different water sources in Ghana

Dry and smoked shrimp constitute important nutrient supplement for the populace in Ghana. Shrimp continues to represent one of the safest forms of muscle protein consumed in the world. However, the attending microbial load from the environment during drying requires concerted efforts to curtail contaminating microbes (fungi, bacteria) and other biodeterio agents (such as insects). In this study, microbiological quality (with particular reference to fungi) was studied before and after gamma irradiation (0, 4, 8 and 10 kGy), with the view of identifying potential mycotoxine-producing fungal species resident in shrimp taken from three different water sources (lagoon, sea, river) which may endanger the health of consumers. Consumer acceptance (preference) tests were performed using conventional sensory evaluation parameters (colour, taste, texture, aroma) on the samples. A structured questionnaire was employed to ascertain biodata, educational background, storage and packaging practices of the traders. The storage stability of the shrimp was determined by sorption isotherms using glycerol: water mixtures to stimulate Environmental Relative Humidity (20, 55, 65, 75, 85 and 95% Eh) for 20 days. Population of fungi was ascertained on two media (Ogee, D RBC) using the conventional decimal serial dilution technique up to 1:104; Total Aerobic Bacteria was determined on Pca at 32 degrees Celsius for 48 hours. Insects in the samples were determined by the Hidden Identification technique; Crude protein was estimated by the Kjeldhal method and total ash was determined using the Carbolite furnace. Percentage fat and moisture contents were determined concurrently using the Miniature Bench Top Nuclear Magnetic Resonance (BTNMR); Elemental composition was estimated by Atomic Absorption Spectrometry (AAS). The Flame Photometer was used in the determination of sodium and potassium contents of samples. Minolta Chroma Meter was used to measure the colour L*a*b value scale. Twenty-six (26) different fungi species were isolated from the shrimp from the different water sources. Fourteen (14) species belonging to 7 genera were isolated from the sea shrimp. Seventeen (17) species belonging to 6 genera were isolated from the riverine shrimp and 12 fungal species belonging to 5 genera contaminated the lagoon shrimp. In all instances, Aspergillus predominated over the other species, followed by Penicillium and Cladosporium. Toxigenic species encountered included A. flavus, (Aflatoxins), A. alutaceus (ochratoxins), P. expansum (Patutin), and F. verticilliodes (fumonisins). The contaminating bacteria were Bacillus cereus and Staphylococcus aureus. Insect infesting the shrimp were Necrobia rufipes, Dermestes maculatus and a mite Lardoglyphus sp. which collectively decreased weight by 43% after incubation for 8 weeks. A dose of 8-10 kGy could kill insects, reduced (by 2-3 log cycles) or eliminated fungi and bacteria load significantly (p≤ 0.05). There were clear differences in the concentration of crude protein, ash, fat, moisture, colour (L*a*b) values, heavy metals and other elements (Mg, K, Na, Zn etc.) due to influence of the type of water body they dwelt. Untrained panelists found no statistical differences (p≥ 0.05) in colour and taste up to 10kGy in the sea shrimp but found differences in aroma and texture. Irradiation up to 10kGy did not affect colour, aroma, texture and taste of the lagoon shrimp. Statistical analysis showed that overall; panelists preferred irradiated shrimp to non-irradiated ones. [au]