The fungi as food and feed are very nutritive since they contain essential and nonessential amino acids. The use of fungi as dietary sources and in fermented beverages is in vogue since pre-biblical times. Archaeological evidence traces association of edible wild mushroom to the inhabitants of Chile, almost 13,000 years ago. However, it was in China where the consumption of wild fungi was first reliably noted and their utilization in production of other food materials, their full potential was not explored until the latter half of the 20th century when it was boosted by the advent of the golden age of industrial microbiology.
Since then, this diverse community represented by yeasts, mushrooms and filamentous fungi have been exploited in a myriad of food products both for human and livestock consumption. Fungi are used in many industrial processes, such as the production of enzymes, vitamins, polysaccharides, polyhydric alcohols, pigments, lipids, and glycolipids. Some of these products are produced commercially while others are potentially valuable in bio-technology. Fungal secondary metabolites are extremely important to our health and nutrition and have tremendous economic impact. In addition to the multiple reaction sequences of fermentations, fungi are extremely useful in carrying out biotransformation processes. These are becoming essential to the fine-chemical industry in the production of single-isomer intermediates. Molecular manipulations have been added to mutational techniques as a means of increasing titers and yields of microbial processes and in the discovery of new drugs. Today, fungal biology is a major participant in global industry.
Bakery products consist of a mixture of flour (usually from cereals especially wheat), with water, salt and sugar, leavened by yeast. Flour is mixed with the remaining ingredients and incubated at about 25oC. The yeast ferments the sugar forming carbon dioxide and alcohol. The released gas causes bubbles by elastic extension of gluten (a protein) in the flour. On baking, the alcohol evaporates. The length of leavening, the quantity of gluten in the flour, the constituents of the grain and the temperature determine the texture and flavor of the bread. In production of cheese presence of visible fungal mycelium is a part of the moldy cheeses favorites among gourmets.
Over recent years, consumption of fungal food had increased on a global basis with rise in public concern about dietary and health issues. Especially, those belonging to the vegetarian community have resorted to eating either freshly cooked mushrooms or processed foods, beverages and dietary supplements of fungal origin. Fruiting body of mushrooms has been consumed directly fresh or processed and used as delicacy. Fungi can be produced technically through fermentative process, through stages of media preparation, inoculation and incubation. The media may be in form of substrates available from cheap valued sources like agro-biomass and industrial waste; though transformed into high value added food and pharmaceutical products. Thus use of fungi is important from economical as well as environmental aspects. Although, the cultivation of macro fungi had flourished in recent years, use of fresh mycelia as food has not still attained the impetus to be popularized on a global scale. Rather, more indispensable is the role of these organisms especially yeast in industrial food production and processing. Fungal cell factories are widely employed in brewing, wine making, and bread making industries due to their inherent capacity of secretion of a wide titer of enzymes into the growth medium.
The limitations imposed by alcohol concentration on the fermentation by yeast is in the ranges of 10-12 percent or 15-16 percent as in the case of sake production and the alcoholic concentrations is increased by distillation. Alcoholic beverages produced using fruit juices include wine, cider, and perry. Single Cell Protein is the name collectively given to a variety of microbial products, produced by fermentation. They can be used to ferment some of the vast amounts of waste materials, such as straws; wood and wood processing wastes; food, cannery and food processing wastes; and residues from alcohol production or from human and animal excreta.
Fungi can be used in new production processes that are themselves less polluting than traditional chemical processes and some species of white rot fungi are already being employed to degrade toxic wastes. Many of these applications are still under development. For example, textile dyes could be produced by fermentation in the future. Many fungi produce pigments during their growth which are substantive as indicated by the permanent staining that is often associated with mildew growth on textiles and plastics. Some fungal pigments have been shown to be anthraquinone derivatives, resembling the important group of vat dyes. Fungi therefore have potential as agents for the direct production of textile dyes or dye intermediates replacing chemical synthesis which has inherent waste disposal problems.
Recent studies have suggested that lignin-degrading or white-rot fungi such as Phanerochaete chrysosporium and Trametes versicolor could replace some of the chemical steps used in paper making. An industrial biopulping/biobleaching process would eliminate the pollution problems associated with the use of chemicals. Lignin-degrading fungi or their enzymes also have the ability to degrade highly toxic organic compounds such as dioxins and PCBs (polychlorinated biphenyls), and could have an important role to play in the remediation of contaminated soils and the disposal of chemical wastes. A recent report also indicates that lignin-degrading fungi can even degrade synthetic textile polymers such as nylon previously thought to be non-biodegradable.
The writers are associated with the Department of Plant Pathology, University of Agriculture Faisalabad, Pakistan.
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