The antioxidative effect of the zizyphus fruit (Ziziphus spina-christi) and Date Seed (Phoenix dactylitera) of var. Mazafati extracts on soybean oil oxidation

The oil oxidation changes the organoleptic characteristics of foods and decreases the nutritional value and shelf life of oils and is harmful to consumer health due to formation of unfavorable compounds in oil. Currently, the most widely used antioxidants are synthetic antioxidants, but their use faced some restriction due to their carcinogenic properties. Hence, natural antioxidants such as tocopherols and ascorbic acid derivatives are widely used as safe natural antioxidants. The aim of the present study was evaluation of antioxidant properties of date palm and Zizyphus extracts and their combined extract on soybean oil oxidation.

In this research, initially the antioxidant effect of individual and combined aqueous extract of the zizyphus fruit and date seed in different concentration was measured and then the effect of the zizyphus fruit and date seed extracts and their selected combination based on previous step, on oxidative stability of soybean oil during storage was evaluated. For this purpose, the extracts were added to free antioxidant soybean oil and oxidative stability of oil was measured at temperature of 63 °c for 32 days using peroxide index, the induction period and also thiobarbituric acid index (TBA) and was compared with synthetic antioxidant BHT. The treatments used in antioxidant experiment were the individual and combined extract of the zizyphus fruit and date seed at two different concentration of 200 and 500 ppm with different ratio of combined extract including 0:100, 20:80, 40:60, 50:50, 60:40, 80:20 and 100:0. In the soybean oil stability experiment the treatments used were ratio of the combined zizyphus fruit and date seed extract of 20:80 at concentration of 200 ppm and two concentration of 200 and 500 pp for individual extract and BHT in two concentration of 100 and 200 ppm. The results were compared in three replications using the completely randomized design, in a factorial design experiment, ANOVA analysis and Duncan test (p < 0.05) by SPSS software (version 16) and the graphs were drawn by Microsoft Excel.

The results of the peroxide value and TBA tests showed there was no synergistic effect in the combined extract (zizyphus fruit :date seed with the ratio of 20:80, in concentration of 200 ppm). Yet in peroxide test this extract showed a significant better effect (p < 0.05) compared to BHT, but in TBA test, it showed similar function as synthetic antioxidant BHT. In individual extract at both concentration of 200 and 500 ppm they were comparable to BHT with the concentration of 100 and 200 ppm.

Results of present study indicates the zizyphus fruit and date seed extracts, as individual or combined extract could be used as an alternative to the synthetic antioxidant BHT.