Evaluation of Antioxidant Activity of Fig (Ficus carica) Pulp and Skin Extract and Its Application in Enhancing Oxidative Stability of Canola Oil

Abstract

This study was carried out to determine the antioxidant activity of pulp (P) and skin (S) extract of two fig varieties of figs (Sabz(G) and Siyah(B)) by subcritical water extraction. The antioxidant activity of the extracts was evaluated by using 2,2′-diphenyl-1-picryl hydrazyl radical, reducing power and rancimat tests. The Siyah variety contained higher levels of polyphenols and flavonoids in comparison with Sabz variety. Generally, Siyah variety revealed higher levels of phenolic compounds and flavonoids. Moreover, the lowest IC50 in DPPH tests and reducing power was related to Siyah fig skin extract, and rancimat test showed no significant difference between antioxidant activity of fig extracts. The efficiency of Siyah fig skin extract for oxidative stability was assessed using peroxide, thiobarbituric acid, conjugate dien, acid value and color indicator in canola oil, compared with synthetic antioxidants of tert-Butylhydroquinone (TBHQ). The results showed that Siyah skin extract had the highest antioxidant activity and were comparable with TBHQ. Furthermore, skin of Siyah fig variety can be considered as a good source of phenolic compounds. Practical Applications Several novel techniques, notably subcritical water extraction, have been developed for the extraction of natural antioxidants from plants in order to shorten the extraction time, decrease the organic solvent consumption and increase the quality of extracts. One of the most important applications of natural antioxidants is retardation or inhibition of oil oxidation. This paper reveals that the natural extracts have antioxidant activity comparable to that of synthetic antioxidants used in oil industry. Therefore, skin of Siyah fig extract can be used to replace synthetic antioxidants.