Effects of Sisal Saponins on Enzymatic Hydrolysis and Fermentation of Lignocellulosic Biomass

Saponins are surface-active glycosides successfully applied to produce sugars via enzymatic hydrolysis and fermentation. However, there are several reports that saponins compromise the integrity of yeast cells, which would limit ethanol titers. In this context, the present study evaluated the role of saponins from sisal (Agave sisalana) on the action of cellulases and yeast within the context of cellulosic ethanol. Microcrystalline cellulose, pretreated coconut fiber samples, and pretreated corncob samples were evaluated as cellulose sources. Sisal saponins increased cellulolytic activity in adsorption (from 20.9 to 46.4%) and enzymatic hydrolysis (33.5 to 63.0%, using alkaline-pretreated coconut fiber as substrate). However, the amount of released sugars remained unchanged in tests with pretreated biomasses. Glucose released in the hydrolysis of microcrystalline cellulose reduced from 22.03 to 19.09 g/L using 10% (w/w) saponins. One percent (w/w) saponins caused an abrupt decrease in the viability of Saccharomyces cerevisiae cells within a few minutes (from 98.07 to 29.57% in 240 min), and ethanol was not produced in the simultaneous saccharification and fermentation. For this reason, sisal saponins have not replicated the success of other types of saponins and are unsuitable for cellulosic ethanol production.