Optimization of Microwave-Assisted Extraction of Phenolic Compounds with Antioxidant Activity from Carob Pods

Abstract

A microwave-assisted extraction (MAE) procedure to obtain phenolic compounds from carob bark was optimized by using response surface methodology. A four-factor, three-level Box–Behnken design with five central points was used to evaluate the influence of temperature, solid-liquid ratio, ethanol concentration, and time in carob bark extraction in terms of antioxidant activity (DPPH) and total extraction yield. Optimal extraction conditions were found using 80 °C, 35% (v/v) ethanol, a ratio of 35 mL/g, and 29.5 min. Total phenolics content (TPC), antioxidant activity (DPPH, FRAP, ABTS), carbohydrate content, and main polyphenols composition (HPLC) were determined at optimal conditions. An experimental total yield of 66.5% was obtained with a TPC value of 33.6 mg GAE/g DW and polysaccharides content of 345.4 mg glucose/g DW. A high antioxidant activity was also shown by the three methods tested. The results showed the potential of carob pods skin as a natural source of phenolic compounds, in particular gallic acid, and the effectiveness of MAE as extraction technique for the revalorization of this agro-food waste.