Effective valorisation of cereal lignocellulosic waste: a review of pretreatment techniques to enhance microstructural modification

Abstract

Food waste biomass from agro-food processing, such as grain husks, represents an abundant and renewable resource with significant potential for valorisation through enzyme hydrolysis. The enzyme hydrolysis process can convert lignocellulosic waste into valuable end products like biofuel, bioethanol, biochemicals, bioplastics, and bio-fertilisers. However, the complex structure of lignocellulose, including tightly bonded cellulose, hemicellulose, and lignin, poses significant barriers to enzymatic hydrolysis and conversion into valuable products. Hence, structural modification, as a pretreatment step before hydrolysis, is crucial in facilitating the efficient conversion of lignocellulosic waste biomass into valuable end products. This review examines the role of various pretreatment methods, including milling, extrusion, chemicals (acid & alkali), steam explosion, ammonia expansion, and biological processes (bacteria, fungi, and enzymes), in breaking down the recalcitrant nature of lignocellulose through structural modification in cereal husk. This review also discusses the resulting changes in microstructure (crystallinity, porosity, and surface morphology) due to various pre-treatments and their aligned effects on the hydrolysis rate and production of high-value fermentable sugars. The novelty of this review lies in the focus on incorporating microstructure-based pretreatment strategies for the underexplored cereal husk, offering new insights into the structure–function relationship that influences the enzyme hydrolysis and valorisation potential. By identifying the gaps in current research and highlighting the fermentation potential of pretreated cereal husks, this review provides a guide to biomass-specific, synergistic and nanotechnology approaches and environmentally sustainable valorisation strategies that support circular economy goals.