Extraction of antioxidants from sweet Thai tamarind seed coat––preliminary experiments Original Research Article

The aim of this preliminary experimental study was to investigate the extraction yield and activity of antioxidants from the seed coat of sweet Thai tamarind, (Tamarindus indica L.). Extractions with supercritical CO2, supercritical CO2 with a 10% ethanol co-solvent as well as with solvent extraction with ethanol and ethyl acetate were carried out. Supercritical fluid extractions were performed over the range 35–80 °C and 10–30 MPa. Shake flask solvent extractions were performed using ethanol and ethyl acetate. It was found that the extraction of (−)-epicatechin with pure CO2 was very low, (≈22 μg of (−)-epicatechin per 100 g of seed coat). The use of a 10% ethanol co-solvent resulted in a much higher yield of (−)-epicatechin, (≈13 mg/100 g), under the best conditions which were found to be 40 °C and 10 MPa. Solvent extraction experiments showed that ethanol has a higher selectivity than ethyl acetate for extraction of (−)-epicatechin; yields of (−)-epicatechin using ethanol were about 150 mg/100 g. The antioxidant mixture extracted from sweet Thai tamarind seed coat using solvent extraction with ethanol was found to be the most active in terms of peroxide value (PV).