Rice husk pretreatment alters fermentable sugar production, aromatic compound profiles, and n-butyric acid fermentation

Abstract Rice husk hydrolysates produced using different pretreatment methods can exhibit different fermentation responses even after adjusting the fermentable sugar concentration to the same level. In this study, dilute-acid, alkaline, ethanol-organosolv, and ball-milling pretreatments were compared for sugar production and subsequent n -butyric acid fermentation by Clostridium tyrobutyricum BAS7. After enzymatic hydrolysis, each hydrolysate was concentrated to 60 g/L total glucose and xylose without adding commercial sugars. The dilute-acid and alkaline hydrolysates produced 26.45 and 26.52 g/L n -butyric acid, respectively, both of which were significantly higher than that of the commercial-glucose control. The alkaline hydrolysate showed a numerically lower maximum cell growth (OD600 6.81) and significantly lower fermentation gas formation (20.00 mL/mL) than the control (OD600 10.78 and 23.23 mL/mL), although the difference in maximum cell growth was not significant after Dunnett’s adjustment. GC×GC-TOFMS profiling showed pretreatment-dependent differences in aromatic-compound profiles, with the alkaline hydrolysate exhibiting the highest relative signal for carboxyl-containing aromatic compounds. Veratric acid supplementation showed a concentration-dependent numerical decrease in fermentation gas formation; however, the differences from the control were not statistically significant. These findings indicate that pretreatment-dependent hydrolysate composition, in addition to fermentable sugar concentration, was associated with downstream fermentation performance.