Grapefruit seeds are rich sources of phenolic compounds which are often considered as wastes of the fruit juice industry. Antioxidant activity of grapefruit seed extract (GSE) was assessed at different levels by determining the peroxide value, antioxidant activity percentage and induction period using the Rancimat test and was then compared in both palm oil and fish oil as very diverse types of oil. The fatty acid composition of these oils was determined and compared using gas chromatography. These types of oil had a significant effect (P<0.05) on antioxidant activity of GSE. In both oils antioxidant activity of GSE increased with concentration. GSE at 2000 ppm exhibited the best effect in preventing peroxide value increase and more antioxidant activity compared to TBHQ in both oils. The average antioxidant activity of GSE in palm oil was greater than that in fish oil. The results of Rancimat test proposed a possible blockade effect on the antioxidant at high temperature. The findings of this research indicated that GSE is an efficient natural antioxidant and a suitable alternative to synthetic antioxidants to preserve oil in low temperatures.
