Effect of flavonoid extracts from grapefruit seeds and peel flour on soybean oil stability

Abstract

The antioxidant activity of the aqueous extracts from grapefruit seed and peel was evaluated. The seeds and peels were transformed into flour and the flavonoids were extracted by means of organic solvents in the following flour/solvent ratios: 05:25; 1:25 and 2:25. Then, single extractions with 25mL of methanol 85% (v/v) were produced. Afterward, methanolic extracts were mixed in proportion 1:1 (v/v) with petroleum ether and stirred until the appearance of two sharp phases. Subsequently, the aqueous phase was extracted with ethyl acetate and two phases were separated. Doses of every phase in proportion of 0.01%, 0.75% and 0.10%, were added to soybean oil. Samples were stored in an air stove at 60°C ± 1°C and the peroxide value was determined every 24 h for the 600h of study. Significant differences were found between treatments (P< 0.05). An antioxidant effect was shown independently of the metabolite source, flour weight/extraction volume ratio or extract concentration (P < 0.05). The major antioxidant effect showed by the treatments were with 0.01% aqueous extract from 0.5:25 seed flour/solvent ratio, and 0.75% aqueous extract from 0.5:25 peel flour/solvent ratio. No treatment showed pro-oxidant effects. In conclusion, the incorporation of flavonoid extracts into deodorized soybean oil permitted the confirmation of its antioxidant performance.