Optimization of supercritical fluid extraction of polyphenols from oats (Avena sativa L.) and their antioxidant activities

This research explores the effects of pressure and temperature on the supercritical extraction of polyphenols, antioxidant capacity, and total polyphenolic content from oats. Ethanol (80% v/v) was used as co-solvent, and experiments were controlled by response surface methodology (RSM). For polyphenols with C6-C1 structures (vanillin and vanillic acid), a maximum yield of 18.2 μg/g oats was obtained. Polyphenols with C6-C3 structures (caffeic, sinapic, coumaric, and ferulic acids) gave up to 1389 μg/g oats; where coumaric and ferulic acids were found in higher quantities. Avenanthramides (AVNs) yielded up to 34.52 μg/g oats, with 2p and 2c being found in higher quantities than 2f. The polyphenols, TPC (1.25 mg GAE/g of oats), and ORAC (117.88 μmol TE/g of oats) gave the highest yields at 38 MPa and 55 °C. Quadratic models adjusted very well, and a maximum polyphenol content of 1437.57 μg/g was predicted. Moreover, correlations among the polyphenols and antioxidant capacity were found, especially with the ORAC. As a result, the method here presented can be a new procedure for the extraction of polyphenols from oats.