Physicochemical Properties of Refined Palm Cooking Oil and Used Palm Cooking Oil

Abstract

Abstract In public restaurants, food frying is conducted in the same oil and recycled for the same usage for several days. However, during household frying, the cooking oil is changed after several usage. Obviously, the conditions of the cooking oil changed depend on frying styles and the types of material fried. In this study, three different cooking oils; refined palm cooking oil purchased from local market (CO), used palm cooking oil collected from household (UCO-H) and from restaurants (UCO-R) were selected to examine the colour, acid value (AV), saponification value (SV), ester value (EV), molecular weight (MW), percentage of free fatty acid (% FFA), density, water and impurities contents. Colour was observed by naked eyes, AV and SV were analyzed based on PORIM Test Method (1995). EV was calculated according to The United States Pharmacopeia USP 29 NF 24, while MW was calculated from SV and AV results. Density was measured at 20 °C, percentage of water content was analyzed by heating and weighing while impurities content was studied by filtering and weighing. The results showed that as frequency of frying increased, the colour of cooking oil become darker from the CO. The AV was always depend on % FFA. The % FFA of UCO-H and UCO-R were differed by 0.35 % and 2.15 % respectively compared to CO (2.20 %). Meanwhile, the density, water content and impurities content were also increased slightly compared to CO. The SV was found increased slightly for both UCO-H (207.41 mg of KOH/g) and UCO-R (204.74 mg of KOH/g) as compared to CO (200.59 mg of KOH/g). The value of ester was remained constant for UCO-R with value 196.04 mg of KOH/g in comparison with the EV of CO which is 196.19 mg of KOH/g. While for UCO-H sample, the EV increased to 202.32 mg of KOH/g. In conclusion, according to the physicochemical characteristics, the colour became darker while AV, % FFA, density, water content and impurities content increased with frying period. However, the SV and EV were not depending on frying period but they changed according to the type of reaction occurred during frying; among the components inside the oil or between oil components with the food contents.