Understanding the Pine Dilute Acid Pretreatment System for Enhanced Enzymatic Hydrolysis

In the United States, loblolly pine is touted as a potential feedstock for biobased product manufacturing, as it is fast growing and abundant in the southeast. To release the sugar content from pine biomass, pretreatment must occur. Dilute acid pretreatment is, among others, a pretreatment method that can be used. Unfortunately, this pretreatment results in the production of inhibitory byproducts, which need to be removed prior to enzymatic hydrolysis and fermentation; the main inhibitors include organic acids predominantly formic and acetic. Rinsing dilute acid pretreated biomass is a way to remove inhibitory byproducts. Buffering capacity of the enzymatic hydrolysis reaction mixture alleviates inhibition due to organic acids, while maintaining a pH environment that is conducive to enzymatic activity. However, the use of buffer salts at commonly prepared concentrations, such as 50 mM, may not be economically viable at production scale and could hinder fermentation due to their chelating capacity. In this study, two enzymatic hydrolysis citrate buffer strengths, 5 mM and 50 mM, were investigated for their effect on the level of saccharification of rinsed (30X) and unrinsed (0X) acid pretreated pine biomass. Buffer strength did not affect saccharification as long as the pretreated biomass was rinsed. Saccharification was still possible in unwashed biomass as long as the buffer concentration was 50 mM, where 65% saccharification was obtained. Although formic acid, acetic acid, HMF, and furfural concentrations were higher in unrinsed hydrolyzates than in their rinsed counterparts, saccharification could still occur, indicating that these compounds are not the sole culprits in conferring inhibition. No hydrolysis was observed when unrinsed biomass was subjected to enzymatic hydrolysis in 5 mM buffer.