Abstract
The present study examined the antioxidative activity of water and ethanol extracts of green and black tea leaves against the oxidation of heated sunflower oil and lard. Oxidation was conducted at 110โ
ยฐC in the Rancimat test. Total polyphenols and catechin contents in tea extracts were measured. The research showed that the total polyphenol content in green and black tea leaves was 205.2 and 148.7โmg/g, respectively. In tea leaves extracts, it ranged between 245.9โmg/g and 837.7โmg/g and depended on the extraction solvent and the kind of tea used (pโ
<0.001). The highest polyphenol content was observed in samples extracted with 95% ethanol, lower contents were found with the use of water. Results showed that the highest antioxidant activity, measured as an induction period, with 1000โppm green tea ethanol extract, was comparable to รกโtocopherol activity in sunflower oil. In lard, the longest induction period was measured with 500 and 1000โppm of green tea ethanol extract. Other tea extract concentrations were significantly less active. Statistical analysis of the tea extract antioxidant activity in lipids in the Rancimat test showed an essential influence of the catechin contents. Further statistical analysis also showed an influence of (โ)โepicatechin gallate (ECG), (โ)โepicatechin (EC), and (+)โcatechinโ
(C) contents in the tea extracts on the antioxidant activity in lipids. It was stated that the antioxidant activity was higher in tea extracts containing high levels of ECG, EC, and C.