The effect of temperature on the phenolic content and oxidative stability of o/w emulsions enriched with natural extracts from Satureja thymbra

Abstract

Sunflower oil-in-water emulsions were enriched with two Satureja thymbra extracts - obtained by ethyl acetate (EAcs) or ethanol (Es), rosmarinic acid (RA), or quercetin (Que), and the effect of storage temperature (5-40 °C) on the emulsions' phenolic content and oxidative stability was studied. HPLC analysis of the extracts indicated RA as the main component. The phenolic content of the emulsions decreased during storage, following first-order kinetics, with a temperature-dependent rate. RA was the main compound that decreased, Que followed a slower decrease and the rest flavonoids remained almost constant. The additives protected the emulsion against oxidation according to the order Es > Que > EAcs > RA. The protection factor ranged from 73 to 81% at 5 °C, but decreased to around 53% for Que and Es, 33% for EAcs, and 22% for RA at 40 °C. Emulsions enriched with extracts from S. thymbra retain their phenolic content and oxidative stability at refrigeration temperatures.

Keywords: Antioxidant factor; Antioxidants; Emulsions; Natural extract; Oxidative stability; Phenolic stability; Quercetin; Rosmarinic acid.