Optimisation of Cellulase Production by Trichoderma reesei Through Solid-State Fermentation on Rice Straw

Abstract

Rice straw is among the most abundant agricultural residues in the world, and Trichoderma reesei is the best-known fungal source of the cellulases that could turn it into fermentable sugar. Growing the fungus directly on moistened straw, a process called solid-state fermentation, is often proposed as a cheap way to make the enzyme, and many reports describe process conditions that were optimised for it. This narrative review asks what the published literature supports about that practice and where it falls short. It draws on work on the biology and regulation of the fungus, the composition and recalcitrance of rice straw, the engineering of solid-state beds, enzyme assay, and the statistical designs used to optimise culture conditions, and it reports no new experimental data. Moisture, temperature, particle size, nitrogen supply and pretreatment all act through a small number of physical routes, notably water availability, heat removal and gas exchange, which is why optima found in one vessel often fail to transfer to another. Activity figures are further limited by assay choice and by the lot-to-lot variability of straw. The review concludes that optimisation of this system is feasible and worthwhile, that reported optima should be read as conditional on substrate, strain, vessel and assay, and that cost and scale-up questions remain largely unanswered.