Antioxidant properties of aqueous and ethanolic extracts of tara (Caesalpinia spinosa) pods in vitro and in model food emulsions

Abstract

The successful replacement of some synthetic food antioxidants by safe natural antioxidants has fostered intensive search for new vegetable sources of antioxidants. In our study the phenol and flavonoid content of extracts of tara pods was determined. The antioxidant activity was also studied by three different analytical assays: the measurement of scavenging capacity against a radical ABTS⁺ , the oxygen radical absorbance capacity (ORAC) and the ferric reducing antioxidant power (FRAP). All analyzed samples showed a good antioxidant capacity, but the use of a solution of ethanol 75% in a 1 h ultrasonic process allowed achieving the greatest quantity of phenolics (0.464 mg gallic acid equivalent (GAE) g⁻¹ dry weight (DW) ) and the highest antioxidant activity measured by the ABTS⁺ and ORAC methods (10.17 and 4.29 mmol L⁻¹ Trolox equivalents (TE) g⁻¹ DW, respectively). The best method for efficient extraction of flavonoids (3.08 mg catechin equivalent (CE) g⁻¹ DW) was a 24 h maceration in cold water. Two extracts obtained with ethanol 75% and water were added to a model food system (oil-in-water emulsion) and the oxidative stability was studied during storage at 38 °C. Oxidation was monitored by determination of the peroxide value. The addition of 48 µg mL⁻¹ ethanol extract to the emulsion delayed oxidation to the same extent as 17.8 µg mL⁻¹ of Trolox, while water extract was only effective in the early stages of the oxidation process. The results of this study indicate that ethanolic tara extracts may be suitable for use in food, cosmetic and nutraceutical applications.