Oxidative stability and rheological properties of nanoemulsions with ultrasonic extracted green tea infusion

Epigallocatechin-3-gallate (EGCG) is considered the most significant tea catechin because it has the highest free radical scavenging activity and because of its role in preventing carcinogenesis. Thus, adding green tea infusion to food products imparts a safe, natural antioxidant that prevents rancidity and promotes good health. Even if mild technologies could be developed to optimize the extraction of EGCG from green tea, questions remain regarding the best means of delivering EGCG through food and its disposition in the body after ingestion. Recent reports indicate that the bioavailability of EGCG is very poor due to its large molecular size and number of hydrogen bonds. The present study demonstrates the use of ultrasound to extract catechins from green tea leaves with improved EGCG yield, and subsequent preparation of water-in-oil (W/O) green tea nanoemulsions with soy, peanut, sunflower, and corn oils. The green tea/peanut oil emulsion displayed the highest oxidative stability. All W/O emulsions examined demonstrated a shear thinning behavior in good agreement with the Carreau model (R-2 = 0.980 +/- 0.033). Values for shear viscosity at a shear rate of 10 s(-1) were found to be compatible with the semi-empirical equation of Larson and McClements, with an effective volume fraction slightly higher than the actual volume fraction and still increasing with homogenization time. Moreover, the specific surface area of the nanoemulsions was very high and with an average value of about 40 m(2)/mL. (C) 2013 Elsevier Ltd. All rights reserved.