Application of raw industrial sweetpotato hydrolysates for butanol production by Clostridium beijerinckii NCIMB 8052

High starch sweetpotatoes (HSSPs) are renewable feedstocks with the potential to support industrially relevant chemical production. Here, three HSSP genotypes (NC-413, NCPUR06-020, and NCDM02-180) and a table-stock variety (Covington) were tested for butanol production by Clostridium beijerinckii NCIMB 8052 in two process configurations, separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF). Results indicated that sweetpotato genotype, preparation (fresh vs flour), and system configuration significantly affected acetone-butanol-ethanol (ABE) fermentation efficiency. Particularly, conversion using the Covington variety showed the highest product yields and robust results with both preparations (0.137 and 0.094 g butanol/g initial starch for fresh and flour preparations, respectively) without requiring pre-processing for phenolic removal with polyvinylpyrrolidone (PVP). On the other hand, cultures with purple varieties NC-413 and NCPUR06-020, with the exception of NCPUR06-020 fresh preparations, required anthocyanin removal to achieve 0.103 g butanol/g initial starch, which represented more than a 1.6-fold increase in butanol concentration compared to purple sweetpotato hydrolysates without PVP phenolic pretreatment. Conversions with the white genotype (NCDM02-180) showed the lowest performance and largest variability under a SHF configuration (0.012 to 0.034 g butanol/g initial starch for fresh and flour, respectively), while butanol yields under SSF conditions (0.069 g butanol/g initial starch) were similar to the other genotypes examined. This study establishes the feasibility of using regionally relevant sweetpotato feedstocks (e.g., non-food-intended varieties as well as table-stock residues or culls) as a source of crude sugars for butanol fermentation and some of the key processing conditions that influence C. beijerinckii culture performance.