Comparative evaluation of some physicochemical characteristics of selected brands of refined edible vegetable oils marketed in Rivers State, Nigeria

Abstract

Globally, people have been over the years faced the challenges of consuming sub-standard edible vegetable oils which affects the health of humans. These issues necessitated this work aimed at assessing the compliance of edible vegetable oils to both international and local specifications. The physicochemical properties of two sets of ten refined edible vegetable oils (Active oil, Golden penny oil, Mammador oil, Sunola oil, Kings oil, Jumac oil, Grand oil, Adan oil, Laziz oil and Power oil) purchased from four different supermarkets and open markets in Port Harcourt metropolitan city, Rivers State, were assessed for their compositional quality. The above-listed oil samples were characterized for free fatty acids, acid value, ester value, saponification value, peroxide value, iodine value, flash point, cloud point, pour point, smoke point, refractive index, specific gravity and moisture content using accepted standard operating procedures. The result indicates that some of the oil samples manifested impermissible value when compared with physicochemical parameters stipulated by the Codex Alimentations Commission of FAO/WHO and the specification of NAFDAC standards. Triplicate batches of the samples were purchased from four supermarkets and open markets and the physicochemical parameters were analyzed in the laboratory using both gravimetric and titrimetric methods. The results obtained for physical properties for both categories of oils: flash point, smoke point specific gravity, refractive index, pour point, cloud point and moisture content were 319.7 ^oC and 314.7 ^oC, 251.7 ^oC and 247.7 ^oC, 0.918 and 0.917, 1.465 and 1.464, -12.12 ^oC and -11.70 ^oC, -4.9 ^oC and – 4.4oC, 0.06 and 0.10 respectively for the oils sold in supermarkets and open markets. Results obtained for chemical properties for both categories of oils: acid value, %FFA, iodine value, peroxide value, ester value and saponification value were; 0.26mgKOH/g and 0.27mgKOH/g, 0.13% and 0.13%, 109.9I₂/100g and 108.30g I2/100g, 0.75MeqO₂/g and 1.18MeqO₂/g, 194.03mgKOH/g and 194.76 mgKOH and 194.47 mgKOH/g and 195mgKOH/g. The parameters studied varied significantly depending on the brand of oil, poor storage, distribution, and marketing conditions of the oils which could express their poor quality. To supply consumers with high-grade oils, frequent monitoring and controls must be put in place by stakeholders to educate consumers and middlemen on where the oils should be stored and/ or marketed to avert the rapid oxidation of the oil.