Can tea extracts protect extra virgin olive oil from oxidation during microwave heating?

Olive oil is a key ingredient in worldwide cuisine. Microwave cooking is also increasingly used as a timesaving technology but it induces severe changes in the lipids, such as hydrolysis and oxidative reactions that lead to quality and nutritional losses. In this sense, the present work intends to verify the potential increased olive oil stability under microwave cooking induced by white and green tea aqueous extracts, rich in antioxidants. Quality parameters (free acidity, peroxide value, K-232, K-270 and Delta K), composition (fatty acids profile, tocopherols and total phenols content), antioxidant activity and oxidative stability were studied during different microwave heating exposure times (0, 1, 3, 5 and 10 min). Until the first 3 min of heating the tea extracts protect olive oil from the oxidative process. However, with higher heating periods the extracts were pro-oxidants, mainly green tea extracts. Globally, and independently from the addition of tea extracts, the olive oils suffered drastic changes in their quality and composition. PUFA content decreased with exposure time as well as antioxidant activity, total phenols and total vitamin E content, and oxidative stability, with higher losses in the olive oils with green tea extracts. Positive correlations were established between the quality parameters and the increasing heating time, and negative correlations with the composition and bioactive and stability indexes. (C) 2012 Elsevier Ltd. All rights reserved.