| dc.description.abstract | Oil was extracted from Nile perch viscera by varying the wet acid rendering method, then the oil characterized for yields and quality. Viscera were obtained from a local fish filleting plant in Nairobi. Temperature of the oil extraction was maintained at approximately 93oC. The acid concentration varied from 0 – 10% and the heating time from 5 – 25 minutes. The oil was evaluated for yield, free fatty acids, oxidative and color qualities to compare the effect of acid concentration and heating time. Statistical analysis (p 0.05) was done using GenStat 13th edition software. There was significant difference in yield, with interaction between acid concentration and heating time, the yield generally declining after 15 minutes. The yield generally increased from 56.0 ± 4.7% at 5 minutes heating without acid to 77.4 ± 1.0% after 15 minutes heating in 2% acid solution, but again generally declining after 15 minutes heating in all acid concentrations. The yield generally declined as acid concentration increased. Heating for 15 minutes produced the highest yield, with no significant difference at 0% and 2% acid concentrations. There was significant difference in free fatty acids (%FFA), with interaction between acid concentration and heating time, the values generally increasing with increase in acid concentration and heating time from 0.46 ± 0.08% for 5 minutes without acid to 0.92 ± 0.08% for 25 minutes heating in 6% acid solution. Heating times of 5 and 15 minutes produced the lowest %FFA at 0% acid concentration, 0.60 ± 0.05% for 15 minutes being significantly higher than 0.46 ± 0.08% for 5 minutes. There was significant difference in peroxide value (PV) with interaction between acid concentration and heating time, magnitude decreasing from 5.51 ± 0.40 to 1.63 ± 0.37mEq O2/kg oil as acid concentration increased. There was significant difference in color intensity, with acid concentrations. Heating time did not produce a significant difference, and so was the interaction between acid concentration and heating time. There was significant difference in color intensity between 0% and subsequent acid concentrations, with a general increase as acid concentration increased. Based on oil yield and quality, 0% acid and 15
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minutes heating is the most suitable combination for mass production of crude oil from Nile perch viscera.
Bulk oil was extracted from the viscera at 93oC for 15 minutes by 0% acid wet rendering. The oil was neutralized, deodorized and winterized to obtain refined (low melting point - LMP) and the high melting point (HMP) fractions for analysis. The oil fractions were analyzed for omega – 3 fatty acids (eicosapentaenoic acid – EPA and docosahexaenoic – DHA), vitamin A, vitamin E, iodine value (IV), saponification value (SV), density, melting point (MP), and smoke point (SP). The crude fish oil was used as control. Statistical analysis (p 0.05) was done in GenStat 13th edition software. The yield of winterized oil (low melting point fraction) was 45.6 ± 0.5% of deodorized, 39.8 ± 0.5% of crude and 19.6 ± 0.5% of raw material weight. There were no significant differences in density and vitamin E (tocopherol) content of the three fractions of oil. There were significant differences in the slip MP, SP, SV, IV and vitamin A (retinol) content of the three fractions of oil. There were significant differences in EPA and DHA contents of the crude, low melting point (LMP) and the high melting point (HMP) fractions of the oil. EPA and DHA values for the LMP fraction (7.02 ± 0.58 and 33.76 ± 4.04% w/w of total fatty acids ) were highest, followed by crude (2.76 ± 0.31 and 9.5 ± 0.16% w/w of total fatty acids) and HMP having lowest (1.2 ± 0.39 and 4.07 ± 0.54). High vitamins A and E as well as omega – 3 polyunsaturated fatty acids (PUFA) contents and high SP make the crude and HMP fractions suitable for cooking. The high amount of LMP fraction has high content of omega – 3 PUFA, making it suitable for use in food, feed and nutraceutics.
The two fractions were studied for storage stability. Each fraction was stored at room temperature (19 – 23oC) for 20 weeks in transparent and amber colored glass containers. They were analyzed for %FFA and PV at the beginning of storage and an interval of a fortnight thereafter, to assess the effect of package color and storage duration. Statistical analysis of data was done at p ≤ 0.05 using GenStat software, 13th edition. There was a general increase in FFA and PV, with significant differences between oil fractions and package color over storage time.
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For FFA, there was no interaction between the oil fraction and package color while for PV there was significant interaction between the oil fraction and package color. FFA increased from 0.26% to 0.59% for LMP fraction in clear package, 0.26 – 0.43% for LMP in red package, 0.22 – 0.85% for HMP in clear package, and 0.22 – 0.69% for HMP in red package. PV increased from 0.50mEq O2/kg oil to 11.65mEq O2/kg oil for LMP fraction in clear package, 0.50 – 10.58mEq O2/kg oil for LMP in red package, 1.01 – 9.94mEq O2/kg oil for HMP in clear package, after 20 weeks; and 1.01 – 6.86mEq O2/kg oil for HMP in red package after 14 weeks. The levels of FFA and PV of low melting point fraction in colored package remained within the CODEX limits of 0.3% and 5mEq O2/kg oil respectively for refined fish oils up to 18 weeks. The FFA of high melting point fraction surpassed the limit after 6 and 10 weeks for transparent and colored packages respectively. The FFA of low melting point fraction in transparent package surpassed the limit after 8 weeks. Only low melting point oil fraction in transparent pack had PV above limit at 18 weeks. Therefore, colored package is the most suitable for both oil fractions studied. In terms of FFA and PV, both high and low melting point fractions can retain good quality at ambient temperatures for 10 and 18 weeks respectively | en_US |
