Effect of microwave-assisted alkali pre-treatment on fractionation of pistachio shell and enzymatic hydrolysis of cellulose-rich residues

BACKGROUND Pistachio shell is a lignocellulosic biomass with a high potential to be converted into chemicals, biopolymers, and biofuels. Alkaline pre-treatment is an effective way to extract hemicellulose and increase the cellulose hydrolysis. However, there are some disadvantages to this process, such as a long processing time and the formation of high amounts of degradation products. Microwave irradiation can be used to enhance the effectiveness of alkaline treatment. In this study, microwave-assisted alkali pre-treatment (MAAP) was carried to fractionate pistachio shell into its valuable components (i.e., hemicellulose and cellulose), and the enzymatic hydrolysis of cellulose-rich residues was performed to produce fermentable sugars. RESULTS The MAAP conditions (microwave power, NaOH concentration, and pre-treatment time) were studied and optimized by Box-Behnken design to obtain the highest hemicellulose and cellulose yields. Optimal pre-treatment conditions were microwave power of 224 W, NaOH concentration of 1.96 N, and pre-treatment time of 2.63 min. Under these conditions, the recoveries were 58.35% and 92.46% for hemicellulose and cellulose, respectively. Additionally, compositional analysis carried out on the solid and liquid fractions obtained from the pre-treatments indicated that the main components in the liquid phases were xylooligosaccharides (XOS) and the solid phases were enriched in cellulose. MAAP enhanced the enzymatic hydrolysis yield, and a maximum glucan to glucose conversion yield of 82.67 mol% was obtained for the solid pre-treated under optimum conditions. CONCLUSION The studied MAAP process could be an effective and viable option to extract hemicellulose from pistachio shell and increase the enzymatic digestibility of cellulose-rich solid residues. (c) 2020 Society of Chemical Industry (SCI)