The effects of ethanol on hydrolysis of cellulose and pretreated barley straw by some commercial cellulolytic enzyme products

Authors: Nghiem, Nhuan; ELLIS, CLYDE - Former ARS Employee; Montanti, Justin

Submitted to: AIMS Bioengineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2016
Publication Date: 11/2/2016
Publication URL: http://handle.nal.usda.gov/10113/63277
Citation: Nghiem, N.P., Ellis, C.W., Montanti, J.M. 2016. The effects of ethanol on hydrolysis of cellulose and pretreated barley straw by some commercial cellulolytic enzyme products. AIMS Bioengineering. 3(4):441-453.

Interpretive Summary: Production of fuel ethanol from renewable biomass feedstocks such as agricultural residues (corn stover) or bioenergy crops (switchgrass) has attracted considerable interest. In this process, the selected feedstock is pretreated with chemicals such as acids or bases. The pretreated material then is subjected to hydrolysis by commercial enzyme products to convert the carbohydrate fractions to fermentable sugars, which subsequently are fermented to ethanol. Normally the hydrolysis and fermentation steps are combined into a process called simulatenous saccharification and fermentation or SSF where the two aforementioned steps are carried out together in a single reactor. In the SSF process, the enzymes are exposed to ethanol over an extended period of time and at increasing levels during the progress of the reactions. Therefore, it is important to know the effects of ethanol at various levels on the activities of the commercial enzyme products used for fermentable sugar production. In this study, the effect of ethanol at levels ranging from 2.5% (volume basis) to 15% (volume basis) on the activities of two recently developed commercial biomass hydrolysis enzyme products, Accellerase® 1500 and Accellerase® XY, was investigated. At low levels, ethanol was found to improve fermentable sugar production in some cases. At higher levels, ethanol had negative effects on the activities of the enzymes tested. However, even at 10% (volume basis), which is expected to be approximately the final level of ethanol in a commercial process using biomass feedstocks, the enzymes still retained at least 50% of their activities. This research will be valuable to companies that are designing and running commercial lignocellulosic ethanol plants because it shows that ethanol concentration impacts enzyme activities, but the effect is not major.

Technical Abstract: The effect of ethanol at levels ranging from 2.5% v/v to 15% v/v on the activities of two recently developed commercial cellulosic biomass hydrolytic enzyme products, Accellerase® 1500 and Accellerase® XY, was investigated. The substrates used for study of the effect of ethanol on Accellerase® 1500 included alpha-cellulose, cellobiose and barley straw pretreated by the soaking in aqueous ammonia method. The initial rates of glucose production and final glucose concentrations obtained at 48 h of hydrolysis were used as the response factors. To study the effect of ethanol on Accellerase® XY, beechwood xylan and the pretreated barley straw were used as substrates. The response factors included the initial rates of xylose production and final xylose concentrations obtained at 48 h of hydrolysis. It was found that ethanol acted as either activator or inhibitor depending on its concentration and the type of substrate used. At 10% v/v, which is expected to be the final concentration of ethanol in a commercial cellulosic biomass-based process, ethanol acted as an inhibitor in all cases. However, even at this ethanol level, both commercial enzymes still retained at least about 50% of their activities.