2-37: Effect of alkaline and acid pretreatments on agricultural substrates for holocellulase production

Biofuels of second generation are produced using agro-industrial residues which are complex materials composed mainly of cellulose, hemicellulose and lignin. The aim of this work was to evaluate among acid and alkaline-pretreatments of sugarcane bagasse, agave bagasse and corn cobs in terms of physical structure changes, lignin removal, production and activity of cellulases and xylanases (commonly denominated holocellulases) for the mutant PR-22 of Cellulomonas flavigena.

Substrates were pretreated in acid and alkaline dilute solutions (1-3% w/v or v/v) and heated at 121 °C for 15 min. After pretreatment, the solid fraction was separated from the slurry, washed till neutralize, then air dried, milled and sieved through pass a 20 mesh and stored until use. The effects of each pretreatment were evaluated by scanning electron microscope (SEM) images, lignin removal and enzymatic assays in shake flasks and STR.

Compared to acid-pretreatment, alkaline-pretreatment removed 20-50% of lignin content and resulted in 23 and 45% higher volumetric xylanolytic and cellulolytic enzymatic activities, respectively (p < 1x10^-4). Moreover, SEM showed that alkaline pretreatment was better in separating and thinning the fibers.

Conclusions:

Alkaline pre-treatment results to be more suitable to remove lignin from the lignocellulosic fibers and enhance higher activities of holocellulases.

Concerning pretreated substrates corn cob is the best substrate to enhance holocellulase activities of C. flavigena PR-22 compared to agave and sugarcane bagasses.