Abstract
A maize (Zea mays L. subsp. mays) diversity panel consisting of 26 maize lines exhibiting a wide range of cell-wall properties and responses to hydrolysis by cellulolytic enzymes was employed to investigate the relationship between cell-wall properties, cell-wall responses to mild NaOH pre-treatment, and enzymatic hydrolysis yields. Enzymatic hydrolysis of the cellulose in the untreated maize was found to be positively correlated with the water retention value, which is a measure of cell-wall susceptibility to swelling. It was also positively correlated with the lignin syringyl/guaiacyl ratio and negatively correlated with the initial cell-wall lignin, xylan, acetate, and p-coumaric acid (pCA) content, as well as pCA released from the cell wall by pre-treatment. The hydrolysis yield following pre-treatment exhibited statistically significant negative correlations to the lignin content after pre-treatment and positive correlations to the solubilized ferulic acid and pCA. Several unanticipated results were observed, including a positive correlation between initial lignin and acetate content, lack of correlation between acetate content and initial xylan content, and negative correlation between each of these three variables to the hydrolysis yields for untreated maize. Another surprising result was that pCA release was negatively correlated with hydrolysis yields for untreated maize and, along with ferulic acid release, was positively correlated with the pre-treated maize hydrolysis yields. This indicates that these properties that may negatively contribute to the recalcitrance in untreated cell walls may positively contribute to their deconstruction by alkaline pre-treatment.
Highlights
Structural polymers within plant cell walls offer potential for long-term sustainable production of renewable fuels, chemicals, polymers, and materials that are currently produced from petrochemicals.Many of the promising conversion pathways for these products are based on cascades of biochemical and/or catalytic reactions starting with the sugars derived from cellulose and hemicelluloses.Abbreviations: FA, ferulic acid; HPLC, high-performance liquid chromatography; pCA, p-coumaric acid; py-MBMS, pyrolysis molecular beam mass spectrometry; S/G, syringyl/guaiacyl; WRV, water retention value. 4306 | Li et al.The recalcitrance of plant cell walls to biological degradation, deconstruction, or conversion is considered to be the most crucial factor to overcome in order to develop successful bioprocessing technologies for lignocellulose conversion to renewable fuels and chemicals (Himmel et al, 2007)
As mentioned in the Introduction, WRV is proposed to act as a proxy variable that may be able to explain a number of phenomenon related to cell-wall polysaccharide accessibility to cellulolytic enzymes
The pre-treated cell-wall hydrolysis yields were positively correlated with the ferulate released by pre-treatment, indicating that breaking of ferulate cross-links between cellwall polymers is an important outcome of pre-treatment
Summary
Structural polymers within plant cell walls (i.e. cellulose, hemicelluloses, and lignins) offer potential for long-term sustainable production of renewable fuels, chemicals, polymers, and materials that are currently produced from petrochemicals.Many of the promising conversion pathways for these products are based on cascades of biochemical and/or catalytic reactions starting with the sugars derived from cellulose (glucose) and hemicelluloses (primarily xylose in angiosperms).The recalcitrance of plant cell walls to biological degradation, deconstruction, or conversion is considered to be the most crucial factor to overcome in order to develop successful bioprocessing technologies for lignocellulose conversion to renewable fuels and chemicals (Himmel et al, 2007). Structural polymers within plant cell walls (i.e. cellulose, hemicelluloses, and lignins) offer potential for long-term sustainable production of renewable fuels, chemicals, polymers, and materials that are currently produced from petrochemicals. In order to generate high sugar yields from the cellulose and hemicellulose within plant cell walls, pre-treatment is required in combination with the subsequent polysaccharide hydrolysis by either enzymes or an acid catalyst (Wyman et al, 2011). Mild alkali pre-treatment of grasses such as maize has shown substantial promise, as these can be employed for both fractionating biomass and generating a pre-treated biomass that is highly amenable to enzymatic hydrolysis (Chen et al, 2013; Karp et al, 2014; Liu et al, 2014)
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