Abstract
The characteristics of soaps prepared from waste edible oil (oils before desgarding used frying oils at home or school refectory) or soybean and rapeseed oils with different degrees of thermal oxidation were investigated. Thermal oxidation oils were prepared by heating in a fryer (National NF-F 100) at 180°C for 20 and 40 h. Waste edible oil collected from home and school was combined. Preparation method of soap, method I. Soaps from fresh and thermal oxidation oils were prepared by heating at 90°C for 3 h with mixtures of 100 g fresh or thermal oxidation oils, 25 g potassium hydroxide and 300 g water. Method II. Soaps from waste edible oil were prepared at room temperature for. 30 d with mixtures of 2500 g waste edible oil, 450 g sodium hydroxide, 2000 g water (added hot water of 500 g every third day) and one cup of left-over rice. They were stored in beakers at room temperature.
Anisidine, carbonyl and peroxide values and content of oxidized fatty acids (fatty substances insoluble in petroleum ether) in soap were determined with fatty acids isolated by acidifying the mixture with hydrochloric acid.
Anisidine and carbonyl values of soaps prepared from thermal oxidation oil were markedly lower than those of thermal oxidation oil. Anisidine and carbonyl values were much higher in waste edible oil soap than in waste edible oil. Oxidized fatty acid content in each soap was similar to that of thermally oxidized waste edible oils. Increase in anisidine, carbonyl and peroxide values was observed during storage.
