Phenolic Inhibitors of Saccharification and Fermentation in Lignocellulo-Starch Prehydrolysates and Comparative Efficacy of Detoxification Treatments

Abstract

The generation of phenolic inhibitors in the prehydrolysates from steam, dilute sulphuric acid (DSA) and lime pretreated root wastes (peels from sweet potato, elephant foot yam, tannia, beet root and greater yam) and vegetable processing residues (peels from ash gourd, pumpkin and vegetable banana and mixed vegetable waste) was monitored. Further, the effect of detoxification agents such as Tween 20, PEG 4000, active charcoal and sodium borohydride in reducing their levels was compared. The aqueous extracts from native biomass contained soluble phenolics at levels of 1.03% to 3.02%. Highest release (12.5-16.2% increase from the values in aqueous extracts of native biomass) of total soluble phenolics (TSPs) into the prehydrolysates was found in steam (60 min.) and DSA (60 min; 121 C) pretreatments, irrespective of the type of biomass, while lime pretreatment resulted in only 1.7-3.1% increase in the phenolics. Maximum quantity of TSPs was removed in 2 h at room temperature (301 C) by Tween 20 (70-81%) or its combination with PEG (73-82%). Active charcoal (2%; 45 C; 1 h) or sodium borohydride (40 mM; 20 min; 301 C) removed only 40-59% and 37-53% phenolics respectively. Loss of reducing sugars was the least (2-3%) in Tween 20 (0.50%) treatment, indicating its superiority over the other treatments.