Bioconversion of xylan in peanut husks to xylitol without detoxification by optimizing the diluted acid hydrolysis process

Peanut husks (PH), an agricultural waste, are a promising feedstock for biorefinery due to their high content of bioactive substances and polysaccharides. In our previous study, we extracted bioactive substances from PH and confirmed that polysaccharides still present in the extracted PH (ePH). Xylan, the main hemicellulose component of ePH, can be converted to xylose via dilute acid hydrolysis, and xylose can be utilized as a fermentation substrate for the production of xylitol. However, the acid hydrolysis process produces fermentation inhibitors that adversely affect xylitol fermentation. Hence, the final goal of this study is to determine the major variables of ePH of hydrolysis to achieve a level that does not inhibit the growth of the xylitol-producing strain Candida tropicalis . Fundamentally, the effects of fermentation inhibitors on the xylitol fermentation of C. tropicalis were investigated. The significant inhibitory effect of acetic acid on cell growth of C. tropicalis began at 2.0 g/L acetic acid. Based on these results, the optimal hydrolysis condition for ePH with low acetic acid productivity was determined to be 70.60 min, 2.57 % H 2 SO 4 , and 75.00 g/L biomass loading, and the ePH hydrolysate was found to contain approximately 8.0 g/L xylose and 1. 46 g/L acetic acid. In conclusion, 1.55 g/L xylitol was successfully produced from ePH hydrolysate, which is the best practice to improve the valorization of agricultural waste. • Xylan in ePH was converted to xylose by dilute acid hydrolysis. • Fermentation of C. tropicalis was inhibited beginning at 2.0 g/L acetic acid. • Major variables of ePH acid hydrolysis (ePHH) without inhibition were derived. • Finally, 1.55 g/L of xylitol was successfully produced using ePHH as carbon source.