9omparison of the effectiveness of various pretreatment methods on the enzymatic hydrolysis of sweet potato ( Ipomoea batatas L.) biomass

Abstract

Lignin, phenolic substances and other interfering constituents in agricultural biomass act as physical barriers and diminish the rate and extent of hydrolytic degradation of cellulose. In order to enhance the enzymatic susceptibility of cellulose substrate, a variety of pretreatment processes prior to cellulose hydrolysis have been investigated. Waste leaves and stems of sweet potatoes have been examined as substrates for the production of fermentable sugars for conversion to ethanol. This investigation considers the effects of a variety of single and multiple pretreatment methods on the rate of enzymatic hydrolysis of stems and leaves by cellulase from Trichoderma viride. For the single pretreatment, each substrate was treated with either 2·0% or 4·0% (w/v) sodium hydroxide at room temperature (24 h), or with 70% (v/v) ethanol at 60°C (3 h), or with methanl, or was extracted directly in 75% zinc chloride (w/v) solution in 0·5% hydrochloric acid at 140°C (12mmin). Multiple pretreatments consisted of the following: methanol or methanol and acetone, sulfuric acid (1%, v/v) followed by sodium hydroxide (4·0%. w/v) or zinc chloride or sodium hydroxide and zinc chloride; ethanol, zinc chloride; methanol or methanol and acetone followed by zinc chloride. Single pretreatments were not promising. However, single or multiple pretreatments of leaves enhanced the enzymatic hydrolysis and yields of glucose. Neither single nor multiple pretreatments was found to be very effective for stem substrates, as untreated stems were highly susceptible to cellulolysis. Among all the pretreatments, those involving zinc chloride in hydrochloric acid generally resulted in higher glucose yields.