Effect of Methanol and Water Extract of African Lettuce (Lactuca taraxacifolia) on Stability of Refined Palm Kernel Oil

Abstract

African Lettuce extract was evaluated for parameters related to its antioxidant activity during twelve months storage of Refined Palm Kernel Oil (RPKO) in white transparent plastic bottles at room temperature (27oC – 33oC). Extracts of Wild Lettuce were prepared by separately soaking dried, ground and sieved African Lettuce into methanol and water in ratio 1:10 for 72 h. The Methanol African Lettuce Extract (MALE) and Water African Lettuce Extract (WALE) were separately added at varying concentrations (200 ppm to 1000 ppm) to RPKO. Another set of RPKO
which contained no additive (0 ppm [control]) and 200 ppm BHT was set up. The colour units and refractive indices of oil samples were immediately determined while Free Fatty Acid (FFA), Acid Value (AV) and Peroxide Value (PV) of RPKO samples were monitored monthly using standard methods for a period of twelve months. The colour of RPKO containing MALE (12.0 – 15.0 units) was higher than RPKO containing WALE (10.5 – 12.0 units) while the colour of RPKO sample containing no additive (0 ppm) was 10.0 units and 11.5 units for RPKO containing 200 ppm BHT. The refractive index of RPKO containing MALE and WALE ranged between 1.454 and 1.455 while that of RPKO containing no additive (0 ppm) and 200 ppm BHT was 1.455. The FFA, AV and PV of RPKO containing MALE and WALE were lower than RPKO containing 200 ppm BHT. The results showed that WALE (Water African Lettuce Extract) is more effective in stabilizing RPKO ( hydrolytically and oxidatively) than MALE.

Keywords: African Lettuce, Refined Palm Kernel Oil, Stability, Quality Assessment Test and Methanol.