Increasing the consumption of essential long chain fatty acids through fortification of yoghurt with Omega-3 pufa from Nile perch oil
Increased incidence of Non communicable diseases (NCD) such as cardiovascular diseases, diabetes and cancer has been associated with decreased consumption of polyunsaturated fatty acids (PUFAs) of the omega-3 series, especially very long chain eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These fatty acids are majorly found in fish and their by-products. Nile perch (Lates niloticus) is one of the fish that dominates the commercial fish market in Eastern Africa and its processing results in generation of large amounts of by-products which are of high nutritional content. This study aimed to develop functional yoghurts; YFH (yoghurt fortified with Omega-3 rich Nile perch fish oil and honey) and YFL (yoghurt fortified with Omega-3 rich Nile perch fish oil and lemon juice) and to evaluate their shelf life properties. Liberation of fish oil from Nile perch fat pads was done using a food grade enzyme Alcalase and in the absence of an exogenous enzyme. Characterization of the fish oil was done by thin layer chromatography and the quality parameters; PV (peroxide value), AV (anisidine value), TOTOX (total oxidation) and FFA (free fatty acids content) determined. Three honey samples and three citrus fruits were analyzed for their antioxidant activity and in both cases; the honey and citrus fruit with the highest antioxidant activity were used in development of the functional yoghurt. Four batches of yoghurt were produced, YFH, YFL, PY (plain yoghurt) and YF (yoghurt fortified with Omega-3 rich Nile perch fish oil only) where the latter two (PY and YF) were used as controls. Yoghurt samples were evaluated for sensory characteristics by a random panel of students. Quality parameters, pH, total acidity and ascorbic acid content were analyzed over one month storage period at one week’s interval. Triplicate experiments were conducted and data analyzed using SPSS software. Hydrolysis of the fish fat pads in the absence of an exogenous enzyme gave a better yield (60.67% wet weight) compared to Alcalase enzyme hydrolysis (48.33% wet weight). The quality parameters of the omega-3 rich fish oil were; Pv (meq/kg) = 4.83 ± 1.75, Av =16.50 ± 2.14, Totox= 26.16 ± 1.09 and FFA (%) =2.16 ± 0.22. A commercial honey sample (Green forest) and lemon juice which had the highest Total Antioxidant content (AEAC) of 312± 2.34 and 197± 3.65 mg/L respectively were used for fortification. The sensory evaluation tests showed that the fortified yoghurt was acceptable to the tasting panel with the best two most preferred flavors being the strawberry plus honey and strawberry plus lemon juice samples with ranks of 4.80 and 4.825 respectively in a five point hedonic scale. During the last week of the one-month storage, the yoghurt honey sample gave the most reduced peroxide values (9.78± 2.65) followed by lemon juice (11.54± 2.59) and the sample without antioxidant giving the highest Pv values (15.54± 0.56). The Av values showed a similar trend. The pH decreased slightly over time in all the samples. The lemon juice fortified sample had the highest ascorbic acid content of 28 mg/100g, all the other samples had much reduced ascorbic acid values below 1 mg/100g. The study indicates that enough fish oil can be obtained from Nile perch fish pads by hydrolysis without the need of using an enzyme since enzymatic hydrolysis decreases oil yield due to the formation of an emulsion. All the quality parameters of the omega-3 rich fish oil were in the acceptable range of 3-20 meq/kg for Pv and 4-60 for Av over the one month storage period. In addition, omega-3 rich fish oil–enriched yoghurt was highly stable to oxidation, with the addition of natural antioxidants such as honey and vitamin C evident by the low Pv and Av values in these samples over the one-month storage period. In conclusion, fortification of yoghurt with the omega-3 rich Nile perch fish oils is therefore a practical approach towards ensuring a constant intake of EPA and DHA which is limited due to the low consumption of fish among many communities in Kenya as well as the high cost of ɷ-3 supplements present in the market.