Hydrothermal hydrolysis of sweet chestnut (Castanea sativa) tannins

Abstract

Sweet chestnut tannins were treated with subcritical water at temperatures from 120 to 300 °C for reaction times of 15, 30 and 60 min. A great influence of temperature and reaction time on the product yield was noticed. Spectrophotometric methods were used to determine the total tannins, phenols and carbohydrates contents and antioxidant activity. Furthermore, vescalin, castalin, vescalagin, castalagin, 1-O-galloyl castalagin, gallic, ellagic and ferulic acids were analysed by HPLC. The results obtained from hydrothermal hydrolysis were compared to results from acid hydrolysis. Finally, the reaction parameters of the hydrothermal hydrolysis process were optimized aimed at obtaining a product with a high concentration of ellagic acid. The optimal conditions for obtaining the highest concentration of ellagic acid of 29.55 % were 250 °C and 5 min. The concentration of ellagic acid in tannin extract obtained by acid hydrolysis was 8.19 %.

Keywords

• sweet chestnut
• subcritical water
• ellagitannins
• ellagic acid
• gallic acid