Storage Stability of Refined Oil From Lake Victoria Nile Perch (Lates Niliticus) Viscera

Abstract

Nile perch (Lates niloticus) viscera oil was extracted by wet rendering method and refined by neutralization, deodorization and winterization. After winterization, the oil was decanted and separated by filtration into a low melting point fraction (LMPF) and a high melting point fraction (HMPF). The two fractions were used to carry out storage stability study. Each fraction was stored at room temperature (19 – 23oC) for a period of 20 weeks in transparent and amber colored glass containers. The oil fractions were subjected to quality tests to assess their storage stability. The effects of package color and storage duration were assessed by analyzing for the content of free fatty acids (FFA) as oleic acid and the peroxide value (PV) at the beginning of storage and at intervals of two weeks during storage. The resulting data were subjected to statistical analysis (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. 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 LMPF in clear package, 0.26 – 0.43% for LMPF in red package, 0.22 – 0.85% for HMPF in clear package, and 0.22 – 0.69% for HMPF in red package. PV increased from 0.50 mEq O2/kg oil to 11.65 mEq O2/kg oil for LMPF in clear package, from 0.5058 mEq O2/kg oil to 10.58 mEq O2/kg oil for LMPF in red package, from 1.01 mEq O2/kg oil to 9.94 mEq O2/kg oil for HMPF in clear package, after 20 weeks, and from 1.01 mEq O2/kg oil – 6.86 mEq O2/kg oil for HMPF in red package after 14 weeks. The levels of FFA and PV of LMPF in colored package remained within the CODEX limits of 0.3% and 5 mEq O2/kg oil respectively for refined fish oils up to 18 weeks. The FFA of HMPF surpassed the limit after 6 and 10 weeks for transparent and colored packages respectively. The FFA of LMPF 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. Results showed that colored package is more suitable for both oil fractions studied. In terms of FFA and PV, HMPF and LMPF can retain good quality at ambient temperatures for 10 and 18 weeks respectively.