THE IMPACT OF CHESTNUT VARIETY ON RECOVERY OF POLYPHENOLS FROM PEELS PRETREATED BY OHMIC HEATING OPTIMIZED BY RESPONSE SURFACE METHODOLOGY

The purpose of this study was to optimize ohmic heating (OH) conditions using response surface methodology (RSM) for maximum recovery of polyphenols from industrial chestnut peel waste. Box-Behnken design (BBD) was applied to investigate the effects of three independent variables, namely electric field (V/cm), heating time (sec) and salt concentration (%). From RSM, optimum pretreatment conditions were obtained as 20 V/cm, 100 sec and salt concentration of 0.32%. The peels of three chestnut varieties (Sariasi, Duzce and Kiraz) were pretreated by these optimal conditions and their polyphenols were extracted using different solvents. Polyphenol contents and antioxidant capacities of peel extracts were dependent on the variety and extraction solvents used. HPLC analysis showed that ellagic acid was the most abundant phenolic compound in all varieties. OH pretreatment had a positive effect on extraction. Additionally, alcoholic extraction had a better recovery effect compared to water. The peel waste of Kiraz variety was found to be a good source for polyphenols.