ABSTRACT
This study examines the effects of microwave on the nutritional value, acceptability and shelf life of Clarias gariepinus and Scomber scombrus. A total of twenty four (24) pieces of fish, twelve pieces each of Clarias gariepinus and Scomber scombrus of same size and weight were purchased from selected markets in Benin city, Edo state. All the fish were processed using microwave oven. Six fish samples were evaluated using Association of Official Analytical Chemist (AOAC, 2000) method to determine the bi-weekly proximate composition for 4 weeks. Organoleptic assessment was also carried out using a 10 point hedonic scale in assessing the taste, aroma, texture, color/appearance by a 15-man panel. The microbial qualities were evaluated using Standard Analytical Techniques to access the bacterial and fungal counts and isolates. The result of the proximate analysis for fresh samples shows C. gariepinus had the highest moisture content (71.00±0.10%), while S. scombrus had the least moisture content (61.07±0.13%), C. gariepinus had the highest crude protein (19.63±0.12%), while S. scombrus had the least crude protein (19.53±0.12%), ash content was highest in S. scombrus (3.43±0.06%), C. gariepinus showed the least ash content value (1.27±0.06%), S. scombrus had the highest lipid content (13.43±0.12%), while the least lipid content was seen in C. gariepinus (7.20±0.10%), S. scombrus had the highest fibre (0.02±0.01%), the least fibre was seen in C. gariepinus (0.01±0.01%), NFE was highest in S. scombrus (1.70±0.10%), while C. gariepinus had the least NFE (0.87±0.06%). Microwave dried sample of S. scombrus had the highest crude protein (64.40±0.10%), fat (23.57±0.06%), ash (7.10±0.10%) and NFE (3.50±0.10%) values immediately after microwave drying. Moisture content (16.17±0.21%) was highest in C. gariepinus. After 4 weeks, S. scombrus had the highest crude protein (60.87±0.15%), while C. gariepinus had the highest moisture content (22.67±0.15%). The organoleptic assessment for microwave dried samples showed that C. gariepinus had the highest points for all the parameters such as appearance (8.47), aroma (8.00), texture (8.67) and taste (8.90). This study shows that microwave drying has positive influence on the nutrition and acceptability of microwave dried C. gariepinus and S. scombrus. The total variable counts (TVCs) of the fish samples increased across the week, this was as a result of some factors that can be controlled or not controlled. The bacterial and fungal load counts was highest (4.2×104, 7.8×103) in fresh C. gariepinus, while fresh S.scombrus had the least bacterial and fungal load counts (3.2×104, 7.0×103). After 4 weeks, bacterial and fungal load counts were highest in C. gariepinus (1.4×104, 1.4×103) and the least bacterial and fungal load counts was seen in S.scombrus (9.5×103, 9.5×102 ). The microbial loads obtained under the duration of this study were below the range of specified microbiological limits recommended by International Commission on Microbiological Specification for Food (ICMSF, 1986), ICMSF (19886) for fish and fishery products, the maximum recommended bacterial counts for good quality products is 5 x 105 (5.7 log10 cfu/g). The bacterial isolates found were Bacillus sp, Streptococcus sp, Proteus sp, Pseudomonas sp, Enterobacter aerogenes, Staphylococcus sp, Klebsiella sp, Escherichia coli and Micrococcus sp. The fungal isolates were Rhizopus stolonifera, Aspergilus niger, Aspergillus flavus, Saccharomyces sp, Candida sp., Fusarium sp, Mucor piriformis and Penicillium sp. This study therefore recommends microwave drying because it has positive influence on the shelf life as a result of a reduction in the bacteria and fungi load counts when stored under ambient storage.
