11 - The roles of fungi in agricultural waste conversion

Summary

Introduction

In recent years, recognition of the importance of biological materials as renewable resources for the production of energy and feed, and as important sources of chemical feedstock for the production of different chemicals, has revived interest in the ancient technology of fungal solid-state fermentation (SSF). In the Orient, commercial SSF is still widely practised for miso, saké, soy sauce and tempe production. Agro-industrial byproducts such as lignocellulosic wastes, corn cobs, sugar cane bagasse and coffee pulp, which frequently create serious environmental problems, could potentially be used as low-cost carbohydrate sources for fungal fermentations; these, in turn, would produce biochemical compounds suitable for the food, chemical and pharmaceutical industries.

Fungi are structurally unique organisms that abound in various ecosystems. They are capable of colonizing a wide range of living and dead tissues, including plants, wood and paper products, agricultural plant residues, and live or dead animal tissues. In composting, fungi colonize a mixture of heterogeneous substrates such as municipal solid waste and cattle manure with straw. Many fungi can grow on solid substrates and secrete extracellular enzymes that break down various polymers to molecules that are then reabsorbed by the fungal colony. Consequently any discussion of fungal biodegradation must cover an extraordinary amount of catalytic capability. Exoenzymes derived from filamentous fungi have diverse roles in nature, being involved in the degradation of many types of agricultural matter. Enzymic activities such as oxidation and hydrolysis are involved in the bioconversion of these wastes.