Peroxide value
One of the most common tests to evaluate progress rate of lipids oxidation is peroxide value. This test measures primary products of oxidation. The antioxidant effects green tea extracts as free and encapsulated in liposome on canola oil during oven test 60ºC for 32 days have been shown in Table 1. The green tea extracts as free and incorporated in liposome were added at 200, 600 and 1000 mg/L. Among samples containing green tea extracts, canola oils with green tea extract liposomes showed higher antioxidant efficiency than free green tea extracts. It can be explained green tea extracts liposomes are protect against unfavorable conditions (Lu et al., 2013). The highest and lowest peroxide value belonged control and 600 mg/L concentration green tea extract liposome (P ≤ 0.05). With increasing green tea extracts to 600 mg/L, antioxidant efficiency also increased but further increasing of extract concentration to 1000 mg/L, may cause to decreased antioxidant efficiency. Wanasundara and Shahidi applied green tea extract in 500 and 1000 mg/L on seal blubber oil and menhaden oil. They found green tea extract, at concentration of 1000 mg/L in both oil samples, had prooxidant effect and said this effect could be because existence chlorophyll (Wanasundara and Shahidi.,1997). Also, Endo et al. reported chlorophyll and their derivatives caused lipids oxidation progress (Endo et al., 1985). Chen et al. studied on the antioxidant effects on ethanolic extract of green, yellow and white, black, dark-green and oolong teas on the heated canola oil at 100°C. The results indicated that green, white and yellow extracts showed higher antioxidant activity in compare to BHT to inhibit oxidation canola oil (Chen et al., 1996). Hassan et al. used of olive leaf ethanolic, methanolic and water extract as natural antioxidant on the canola oil. The lowest peroxide value related to ethanolic extracts followed by methanolic and water extracts (Hassan et al., 2013). Koketsu and Satoh compared antioxidant effects of green tea polyphenols at 40 and 60 mg/L and tocopherol in the 200 mg/L concentration on the soybean oil. Green tea polyphenols showed stronger antioxidant effects as compared tocopherol. They reported induction time for reaching a peroxide value 100 meq/kg was 27, 24 and 16 for control and oil samples with 40 and 60 mg/L green tea polyphenols (Koketsu and Satoh., 1997).
Table 1