Dong Hui, Sousa Leonardo da Costa, Ubanwa Bryan, Jones A Daniel, Balan Venkatesh
Department of Chemical Engineering and Material Science, Michigan State University, Lansing, MI, United States.
Department of Engineering Technology, College of Technology, University of Houston, Sugarland, TX, United States.
Front Chem. 2022 Jan 21;9:826625. doi: 10.3389/fchem.2021.826625. eCollection 2021.
Lignin-carbohydrate complexes (LCCs) in the 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 the 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 the 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 four- to five-fold when subjected to commercial enzyme hydrolysis, yielding a sustainable feedstock for producing biofuels, biomaterials, and animal feed. Animal feed trials on dairy cows have demonstrated a 27% increase in milk production when compared to a control feedstock. However, the presence of carboxamides 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 carboxamides. The three industrial byproducts were first treated with calculated amounts of alkali such as NaOH, Ca(OH), 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 at both 10 and 20% solids loading. AFEX pretreatment of de-esterified BSG, HFM, and DDGS produced twofold higher glucan conversion than respective untreated biomass. This new discovery can help overcome potential regulatory issues associated with the presence of carboxamides in ammonia-pretreated animal feeds and is expected to benefit several farmers around the world.
植物细胞壁中的木质素 - 碳水化合物复合物（LCCs）负责抵抗微生物产生的生物质降解酶。文献报道了四种主要类型的木质素 - 碳水化合物键，即苄基醚、苄基酯、苯基糖苷和乙酰酯键。植物细胞壁中的酯键对碱性预处理不稳定，如氨纤维膨胀（AFEX），它使用液态或气态氨来裂解植物细胞壁中的这些键并降低生物质的难降解性。在AFEX预处理过程中会发生两种相互竞争的反应，即水解和氨解，产生不同的脂肪族和芳香族酸及其酰胺对应物。已知经过AFEX预处理的草类和农业残留物在进行商业酶水解时，生物质向糖的转化率会提高四到五倍，从而产生用于生产生物燃料、生物材料和动物饲料的可持续原料。对奶牛进行的动物饲料试验表明，与对照原料相比，牛奶产量提高了27%。然而，如果原料中羧酰胺的含量超过一定浓度，食用后可能会促进动物的神经毒性。因此，在美国将AFEX预处理的生物质商业化用作动物饲料需要克服相关的监管障碍。本手稿展示了一种改良的预处理方法，用于提高工业副产品的消化率，如啤酒糟（BSG）以及由BSG和干酒糟及其可溶物（DDGS）生产的高纤维粉（HFM），同时避免羧酰胺的产生。这三种工业副产品首先用计算量的碱（如NaOH、Ca(OH)₂或KOH）处理，然后进行AFEX预处理。我们发现，在10%和20%的固含量下，4%的碱比2%的碱更能有效地使BSG和DDGS脱酯。对脱酯后的BSG、HFM和DDGS进行AFEX预处理，葡聚糖转化率比各自未处理的生物质高出两倍。这一新发现有助于克服与氨预处理动物饲料中羧酰胺的存在相关的潜在监管问题，并有望使世界各地的众多农民受益。
