EFFECT OF EXTRACTION CONDITIONS ON FLAVONOIDS, TANNINS, ANTIOXIDANT AND ANTIMICROBIAL ACTIVITIES OF CHESTNUT OUTER SHELLS (CASTANEA SATIVA MILLER)

Background. During the chestnut processing, are generated high amounts of by-products such as chestnut outer shells. They are a promising source of bioactive compounds. This study aimed to evaluate the presence of bioactive compounds in chestnut outer shells (Castanea sativa Mill.), to valorize this by-product. Material and methods. Several extraction procedures were used, specifically different solvents (water, ethanol:water (80:20) and acetone:water (80:20)), combined with two extraction methods (stirring (ST) and ultrasounds (US)) and extraction times. Flavonoids, hydrolizable and condensed tannins, antioxidant activity, antimicrobial activity were determined in the extracts. HPLC-PDA analysis was made to identify some phenolic compounds. Results. The acetone:water (80:20) mixture was the best solvent to extract flavonoids and condensed tannins. With this solvent, the highest total reducing capacity, DPPH radical scavenging activity, and reducing power were also obtained. On the contrary, the most suitable extraction solution for hydrolysable tannins was ethanol:water (80:20). Gallic, (+)-catechin, and tannic acids were detected by HPLC-PDA. Only the extracts obtained by the US exhibited antimicrobial activity. Conclusion. It was stated that chestnut outer shells have high amounts of bioactive compounds. In the extractions, the solvent plays a higher role than the method applied.