M.A. Thesis:

studying antioxdant activity of tomato leaves extract and its effect on the stabilization of soybean oi

There are many ways of preventing oxidation of oils, one of which is the addition of synthetic antioxidants to them. However, given the fact that synthetic antioxidants have adverse effects , such as mutagenic and carcinogenic effects , on the human body, it seems necessary that research and studies should be carried out with the purpose of replacing synthetic antioxidants. In this research, we first obtained methanol extracts of tomato leaves and identified their constituents. The extracts were then added at various concentrations (200, 400, 600, and 800 ppm) to purified antioxidant-free soyben oil. The inhibition of the activity of the free radicals by the extracts and the oxidative stability of the oil at 65 degrees centigrade were studied for seven days by measuring the peroxide index, the TBA index, the number of conjugated diene, and the duration of induction. Finally, the activities of the extracts were compared with those of the synthetic antioxidant TBA that, at the concentration of 200ppm, had been added to the purified canola oil. In general, results obtained showed that addition of 200 to 800 ppm extracts of tomato leaves to soyben oil at a given storage time increased the oxidative stability index, the quantities of polyphenolic compounds, and the inhibition of the activities of the free radicals in the oil, but decreased the peroxide index, the TBA index, and the number of conjugated diene. On the other hand, at a given concentration of the extracts, the peroxide index, the TBA index, and the number of the DNA conjugates increased by increasing the storage period of the oil from one to seven days, but the duration of induction decreased. Therefore, results obtained from investigating the oxidative stability of the oil containing various concentrations of the extracts indicated that extracts at the concentration of 200 ppm, as compared with the other concentrations of extracts and the control sample, were more effective with respect to the oxidative stability of soyben oil. The reason for this was that they contained more of polyphenolic and tocopherol compounds, and were more effective than the BHT synthetic antioxidant added at the concentration of 200 ppm to the oil. Therefore, extracts of tomato leaves at the concentration of 800ppm can be introduced as a suitable replacement for synthetic antioxidants.

Keywords: Key words: Natural antioxidants, tomato leaves, soyben oil, oxidative stability