Antioxidant activity of sour orange peel extract and its effect on lipid oxidation in raw and cooked fish Hypophthalmichthys molitrix

Citrus peel, a by-product of fruit juice industry, is a source of natural antioxidants. The search for natural antioxidants for use in food technology, cosmetics, and pharmaceutical science has become a major industrial and scientific research challenge in recent decades. The objective of this study was to determine the antioxidant activity of the inner sour orange peel (mesocarp) extract, the antioxidant stability of the extract by the ferric reducing antioxidant power (FRAP) method, and its protective effect on lipid oxidation in raw and cooked fish by the thiobarbituric acid reactant substances test (TBARS) technique.

An ethanol extract of the inner sour orange peel (mesocarp) was prepared. Samples of the aqueous solution of the extract were then stored for 1 month under different conditions (light, room temperature,, dark room temperature, refrigerator, and freezer). The antioxidant activity and stability of the samples were measured by the FRAP assay and their short- (90 minutes) and long-term (14 days) protection effect on lipid oxidation was evaluated using the TBARS test.

The initial FRAP value of the 0.1% aqueous solution of the extract at room temperature (570 µM) decreased by 14% after one month (p=0.007). The change in the FRAP value of a 0.005% aqueous solution of vitamin C under the same conditions was a 77% decrease (p=0.000) from an initial value of 541 µM. The data also showed that the TBARS value of the raw fish samples containing no extract increased from 1.32µM to 3.173 µM after 14 days, while in presence of a 5% aqueous solution of the extract the increase was from 0.92 µM to 1.09 µM (p<0.05). Under the same conditions, the increases in the TBARS value of the cooked fish samples were also significant─from an initial value of 2.28 µM to 5.85 µM (p=0.000) and from 1.77µM to 3.11 µM (p=0.000) in the absence and in the presence of a 5% aqueous solution of extract, respectively.

The results show that sour orange mesocarp extract has antioxidant activity with high stability during storage and a protective effect on lipid oxidation.