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