Impact of ecofriendly pretreatments on lignocellulose properties and its digestibility by a hydrolytic microbial consortium

Lignocellulose (LC) valorization can be considered as one of the main concerns of this century to overcome fossil energy dependence. In the context of carboxylates platform, LC valorization is achieved by anaerobic consortia to produce carboxylates (or volatile fatty acids, VFA) such as in digestive natural ecosystems. The major limits to LC hydrolysis are cellulose crystallinity, lignin complexity as well as the complex arrangement of LC constituent polymers. To counter these barriers and increase biomass digestibility, the use of dry-pretreatments such as impregnation with chemicals at high biomass concentration appear as a promising technology allowing lower energy and chemical consumption. 

The aim of this study is to assess the impact of eco-friendly dry-pretreatments of wheat straw on LC digestibility by a rumen microbial consortium. Four pretreatments were tested: (A) 2mm milling; (B) 100 µm milling; and 5% NaOH impregnation at high LC concentration combined with (C) 2mm or (D) 100 µm milling. For all treatments, we compared their effects on LC composition (ATR-FTIR, porosity, crystallinity…) and on the dynamic of microbial degradation, considering carboxylate production, enzymatic activities (xylanase and CMCase) and functional diversity analysis (16S rDNA and rRNA sequencing and transcription of functional genes).

Our data showed that NaOH impregnation increases initial VFA production rate (whatever particle size). Compared to no-chemical treatment, these rates were multiplied by 2.6 and 3.5, respectively, for (C) and (D) pretreatments. During this presentation substrate structure and composition effects on biological acidogenic potential will be discussed regarding the microbial diversity adaptation and enzymatic behavior.