Edible Fungi And Recycling Of The Wastesresidues

Mushrooms are highly perishable and have short shelf life ranging from few hours to days depending upon the species and the storage environment. Weight loss, blackening, veil-opening, and microbial spoilage are the common undesirable postharvest changes besides many physiological and biochemical changes (Bano et al. 1997; Rai and Saxena 1989a; Saxena and Rai 1989). Mushrooms require utmost postharvest care like proper handling, packaging, precooling, cool-chain transport, and storage till consumed. Modified atmosphere packaging (MAP), controlled atmosphere packaging (CAP), and modified humidity packaging (MHP) of the button mushroom have been described by Anantheshwaran and Ghosh (1997). Individual Quick Frozen (IQF) mushrooms are gaining popularity with other frozen vegetables in the super markets.

Postharvest technology of mushrooms has been dealt in detail by many authors (Bano et al. 1997; Lal Kaushal and Sharma 1995; Saxena and Rai 1989). Mushrooms are delicate, contain 90% water, rich in phenolics and have very active phenol oxidase and protease activities. They lack protective covering of suberin or cuticle, unlike fresh fruits and vegetables. Postharvest physiological and biochemical changes do take place at very fast rate. Storage in package films, sodium alginate coating, chemical preservation, lactic acid fermentation, irradiation, steeping preservations have been attempted to varied levels of success for short-term preservation of mushrooms. But dehydration and canning are the most common forms of long-term storage and trade in mushrooms; while canning is the most common method for the button mushroom, drying is resorted to for storage and trade of all the specialty mushrooms. Button mushrooms are also freeze-dried in limited quantities. However, improvements in solar dehydration, cabinet tray drying, and tunnel drying technologies of mushrooms are needed to produce better product. Of late, many attempts have been made to produce value-added mushroom products like pickles, soup powder, ready-to-use mushroom curry, nuggets, biscuits, etc.; in future we may witness more of such products.

There are very few wastes of lignocellulosic nature of agro-forestry origin, which can not be used for growing one or the other mushroom. Poppe (2000) has compiled the information on various agro-wastes, which have been used for growing mushrooms. Residues left after obtaining the main product (e.g., grains, cotton, sugar) pose problems of their disposal and many may prove to be environmental hazards. Cultivation of various edible fungi on these wastes represents one of the unique recycling mechanisms where hardly any residue is left unexploited in one form or the other. The substrate left after growing the mushrooms is though often called "spent mushroom substrate" (SMS), which is a misnomer and "post-mushroom substrate" (PMS) is a more appropriate term because it is not "spent" and can be further decomposed by new set of organisms. Many efforts have been made towards profitable utilization of the PMS. The subject has recently been reviewed (Ahlawat and Rai 2002; Levanon and Danai 1997a). PMS of one mushroom can be utilized for growing other mushroom after suitable treatments. The PMS of the oyster mushroom is fed to cattle as feed and the dung obtained is used for biogas production; slurry of biogas plant is used as casing material for the button mushroom and PMS of button mushroom including casing fraction is decomposed in composting pits to be used as manure for raising the crop which was used to grow the primary mushroom, in this case the oyster mushroom (Table 4). In Israel, the above system of complete recycling of wastes has been successfully developed and adopted by the growers (Levanon and Danai 1997b). PMS, especially of the button mushroom, after suitable treatment like recomposting, has proved very good manure for raising not only the horticultural crops but also the major crops; it can also be used for biogas production. As mentioned earlier, the PMS of the oyster mushroom is a very good cattle feed with improved protein content and digestibility. Post-mushroom substrates have also been used for reclamation of soil and bioremediation of soil and water (Ahlawat and Rai 2002). Cultivation of edible fungi has the above mentioned economic as well as environmental advantages; it represents the production of food (mushroom) feed, fuel

Table 4 Recycling mushroom substrates and wastes

Recycling course Main product Waste/byproduct

Table 4 Recycling mushroom substrates and wastes

Recycling course Main product Waste/byproduct

Cultivation of cotton/wheat

Grains/fibers

Wheat and cotton straw

Cultivation of oyster mushroom on straw

Oyster mushroom

Spent mushroom substrate (SMS)

SMS as cattle feed

Meat or milk

Manure

Manure for biogas production

Biogas (energy)

Slurry "Cabutz"

Cabutz as casing soil for button mushroom

Button mushroom

SMS

SMS composted for organic farming

Organic food crops

No further waste from SMS

Source: Levanon and Danai (1997a).

Source: Levanon and Danai (1997a).

(biogas), and fertilizer (manure) by complete recycling of the lignocellulosic wastes of agriculture or forestry origin.

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