Comparative Alterations in the Compositional Profile of Selected Root and Vegetable Peels Subjected to Three Pretreatments for Enhanced Saccharification

Lignocellulosic feedstocks have gained worldwide interest as alternative biofuel source in the context of squeezing petroleum resources, enhanced environmental pollution from greenhouse gases and resulting climate change. The potential of agricultural processing residues such as root and vegetable peels (beet root, greater yam, pumpkin and vegetable banana) for bioethanol production was investigated through an understanding of their compositional profile and efficacy of three pretreatments in altering their composition and reducing biomass recalcitrance. Starch was the major polysaccharide in the residues (range: 25-37%), followed by cellulose (18-22%) and hemicellulose (15-20%). While dilute sulfuric acid (DSA; 121°C ; 0.102 MPa) hydrolyzed starch and hemicellulose to a high extent, steam pretreatment of moist residues (40 % and 50 % MC) at 100 °C also facilitated hemicellulose and starch solubilization. On the contrary, lime pretreatment retained most of the cellulose, hemicellulose and starch in the pretreated residues. Delignification was the highest (28- 37%) in steam pretreated residues, with minimal effect in DSA and lime pretreatments, necessitating lignin binding surfactants during saccharification in the latter. Reducing sugar content in pretreated liquors and Pretreatment Efficiency (%) were the highest (40-45 g L-1 and 57-64% respectively) in the DSA pretreatment. The study showed that as the pretreated liquor DSA and steam pretreatment was rich in fermentable sugars, whole slurry saccharification would be beneficial for maximizing the bioethanol yield.