A Comparative Analysis of the Quantity and Quality of Oil Extracted from Five Commercially Important Freshwater Fish Species in Kenya

Abstract

Fish is an important source of relatively cheap protein. The Kenyan fisheries and aquaculture sector contributes about 0.8% of the Gross Domestic Product (GDP) and this has created direct employment opportunities to over 500,000 people.Generally, there is a huge fish procesing industry that generate huge amount of solid waste and by-product.Some of the solid waste and by-products can be a valuable source for extraction of health promoting fish oil which is rich in polyunsaturated fatty acids (PUFA), especially omega-3 (n-3) fatty acids. Therefore, this study aimed at increasing avenues for value addition of fish products and byproducts through oil exploitation, thus reducing fish waste in landing sites and increasing the overall percentage contribution of fisheries to the Country’s GDP. This study compared the quantitative yields and quality (oxidative stability) of oil extracted from five inland freshwater fish species namely: Nile perch Lates niloticus, Common carp Cyprinus carpio, African catfish Clarias gariepinus, Marbled lungfish Protopterus aethiopicus, and the Nile tilapia Oreochromis niloticus. Basic biological attributes (feeding habits and condition factor) of the five selected species were also assessed prior to the commencement of oil extraction. Fish oil from the various body parts (head, frame, fillet, tail and body cavity) in all the five fish species was extracted using the conventional method of cooking, pressing and centrifugation to determine quantitative yield. The extracted oil was subjected to a composition test (iodine value) and quality tests which included both a hydrolytic degradation test (acid value) and oxidative stability tests (peroxide value and p-anisidine value). Iodine value, acid value, and peroxided value tests were done using titrimetric methods and p-anisidine value test performed using colorimetric method. The results of biological attributes indicated that the exponent ‘b’ (slope) of all the fives species was significantly less than three (b<3, P<0.05) therefore exhibiting negative allometric growth patterns. Relative condition factor ‘Kn’ was greater than one and did not differ significantly between species (Kruskal-Wallis test, p>0.05) indicating that all species were in good condition in their natural habitats. Results of fish oil yields showed that in all the species the body cavity had the highest yield except for P. aethiopicus which yielded more oil from the tail. The quality test results were significantly within their respective set limits, except for C. gariepinus acid value that was higher than the set limit of 7–8 mg KOH/g. This study concluded that three fish species; L. niloticus, C. gariepinus and C. carpio have the potential for oil exploitation from their body cavities while P. aethiopicus commercially viable oil from both the body cavity and tail.