Effect of Sodium Hydroxide Pretreatment on Lignin Monomeric Components of Miscanthus x giganteus and Enzymatic Hydrolysis

The objective of this research was to study the influence of delignification, caused by NaOH, on lignin chemistry. Miscanthus x giganteus samples were pretreated with various concentrations of sodium hydroxide (0.5, 1.0, and 2.0%, w/v) at different pretreatment times (15, 30, and 60 min) in batch systems. Results indicated that NaOH had a significant effect on lignin removal with delignification ranging from 42.3 to 84.6% depending on the severity of pretreatment. Nitrobenzene oxidation was used to investigate changes in lignin chemistry of pretreated M. giganteus by analyzing syringyl to guaiacyl ratio (S/G ratio) and p-hydroxyphenyl to guaiacyl ratio (H/G ratio). The S/G ratio of pretreated Miscanthus increased from 0.64(unpretreated sample) to 0.77 while the H/G ratio decreased from 0.48(unpretreated sample) to 0.28 at 0.5% NaOH pretreatment suggesting that H unit of lignin was most susceptible to NaOH pretreatment. The data also suggested that NaOH concentration was a critical factor in changing lignin chemistry of pretreated Miscanthus. A better understanding of the correlation between pretreatment severities, changes in lignin chemistry, and enzymatic hydrolysis efficiency subsequent to pretreatment of herbaceous grasses warrant further investigations. [GRAPHICS] .