AUTHOR=Dong Hui , Sousa Leonardo da Costa , Ubanwa Bryan , Jones A. Daniel , Balan Venkatesh 

TITLE=A New Method to Overcome Carboxyamide Formation During AFEX Pretreatment of Lignocellulosic Biomass

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 9 - 2021

YEAR=2022

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2021.826625

DOI=10.3389/fchem.2021.826625

ISSN=2296-2646

ABSTRACT=Lignin-carbohydrate complexes (LCCs) in plant cell wall are responsible for providing resistance against biomass-degrading enzymes produced by microorganisms. Four major types of lignin-carbohydrate bonds are reported in the literature, namely, benzyl ethers, benzyl esters, phenyl glycosides and acetyl ester linkages. Ester’s linkages in plant cell wall are labile to alkaline pretreatments such as Ammonia Fiber Expansion (AFEX), which uses liquid or gaseous ammonia to cleave those linkages in plant cell wall and reduce biomass recalcitrance. Two competing reactions, notably hydrolysis and ammonolysis, take place during AFEX pretreatment process, producing different aliphatic and aromatic acids, as well as their amide counterparts. AFEX pretreated grasses and agricultural residues are known to increase conversion of biomass to sugars by 4- to 5-fold when subjected to commercial enzyme hydrolysis, yielding a sustainable feedstock for producing biofuels, biomaterials, and animal feed. Animal feed trials on dairy cows has demonstrated a 27% increase in milk production when compared to a control feedstock. However, the presence of carboxyamides in feedstocks could promote neurotoxicity in animals if consumed beyond a certain concentration. Thus, there is the need to overcome regulatory hurdles associated with commercializing AFEX pretreated biomass as animal feed in the United States. This manuscript demonstrates a modified pretreatment for increasing the digestibility of industrial byproducts such as brewer’s spent grains (BSG) and High Fiber Meal (HFM) produced from BSG and Dry Distillers Grains with Soluble (DDGS), while avoiding the production of carboxyamides. The three industrial byproducts were first treated with calculated amounts of alkali such as NaOH, Ca(OH)2 or KOH followed by AFEX pretreatment. We found that 4% alkali was able to de-esterify BSG and DDGS more efficiently than using 2% alkali both at 10% and 20% solids loading. AFEX pretreatment of de-esterified BSG, HFM and DDGS produced two folds higher glucan conversion than respective untreated biomass. This new discovery can help overcome potential regulatory issues associated with the presence of carboxyamides in ammonia-pretreated animal feeds and expected to benefit several farmers around the world.