Fungi : An alternate source of high value food
Authors: Manas Kumar Bag, Manoj Yadav, Aravindan S., S. Lenka, Arup Kumar Mukherjee.
ICAR- National Rice Research Institute, Cuttack 753 006, India
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Today, there is wider acceptance to diversify our food basket with new sources of food to attain nutritional security. Thus it is important to explore the wild biota like uncultivated edible mushrooms, tubers, vascular and non-vascular epiphytes to identify future food. Several species of fungi are used as food stuffs by the tribal communities in different parts of the world. They are ideal food, incomparable to any other conventional vegetables because of its richness in protein, minerals, dietary fibre, vitamins and almost free of fatty acid and cholesterol. Fungi are an ideal food because of its high content of protein (typically 20-30% crude protein as a percentage of dry matter) which comprises of almost all of the amino acids, essential to both human and animal nutrition. Easily digestible fungal biomass provides a source of dietary fibre. Though filamentous fungi, in contrast to yeasts, have relatively low vitamin content, but contain B-vitamins and low in fat. But the most important aspect of all fungal food is that it is virtually free of cholesterol. Fungal protein foods compete successfully with animal protein foods (i.e. meat) on health grounds.
Besides play an important role in brewing industry, yeasts play a dominant role in food industry also as essential ingredient for bread making and important sources of single-cell protein and dietary supplements. Thus these fungal activities are vital to human existence, particularly in the west where life without bread and wine would be miserable. These support massive industries (annual global consumption of ethanol is currently 30 billion litres). Traditional solid state fermentations for producing mushrooms and other food products and in recent years the Quorn fermentation provide us with a sufficient range of examples of filamentous fungi being almost equally crucial to human affairs (Table 1). Being a rich source of nutrition and being fat-, cholesterol-, and gluten-free and very low in sodium content; mushrooms are gaining popularity among health-conscious consumers. The global market for mushrooms was valued at $29,427.92 million in 2013. Projected to growth is from CAGR of 9.5% from 2014 to $50,034.12 million by 2019 (Annonymous, 2015).
The total number of edible and medicinal fungi is over 2,300 species. Cultivated mushrooms have become popular with over 200 genera of useful macro fungi in the world. Out of 1097 species of edible fungi 820 used as pure food. Fungi used as food in our diet are mostly mushrooms, morels and truffels. Popular mushrooms are the following fungi: Agaricus bisporus, Calocybe indica, Lentinus edodes, Pleurotus ostreatus, P. sajor-caju, Termitomyces sp., Volvariella volvacia and Morchella esculenta, M. rotunda also known as ‘morel’. The most common ones that are produced and consumed are Agaricus bisporus, Lentinula edodes, and Pleurotus spp. and accounted for nearly 76% of the global mushroom market size in 2013. Besides these, ascomycetous fungi, T. melanosporum, Lycoperdon spp., Calvatia spp., Auricularia auricular-judae and Ramaria apiculata grown on conifers are other edible macro fungi.
The most popular is white button mushrooms (Agaricus bisporus, Calocybe indica), grown all over the world and account for 35-45 % of the total mushroom production. This is also known as meadow mushroom. In India, large units with production capacities between 2000 – 3000 tonnes / annum, have been set up mainly as export oriented units in the southern, western and northern regions. A large number of small units without climatic control equipment exist throughout India and function during the autumn and winter months only. A big gap exists between the demand and supply position of white button mushrooms in the United States and European market. India exports the highest quantity of the mushroom produced in the country to USA. Netherlands and China account for 60% of the export of mushrooms. Germany is the largest importer and France and UK are large producers as well as consumers (NHB, 2014).
After Agaricus, Shiitake Mushroom (Lentinus edodes) is the second most cultivated mushroom in the world. Shitake also known as inky-cap mushroom, Japanese mushroom, Chinese mushroom and mushroom of the forest. Besides China and Japan, Shiitake is cultivated widely in Taiwan, Thailand, Korea, Singapore as well as Holland, the United States and Canada. Shiitake is used extensively in a vegetarian diet because presence of good quality protein complement to essential amino acids. Its active ingredient, Lentinan (a polysaccharide), has been shown to reduce cancer and cholesterol. The Shiitake Mushroom is as common in Asian countries as Agaricus bisporus is in the West. Its cultivation method is similar to that of P. ostreatus.
The Paddy Straw mushroom (Volvariella volvacia), light to dark gray, is large and if allowed to mature, its cap often exceeding 5" in diameter. When young, the mushroom is entirely enclosed in a white, egg-like structure called the volva. As the mushroom develops, the stalk will elongate and push the cap upward, thereby rupturing the volva, leaving only a cup-like structure at the base of the stalk. Many Chinese recipes require this mushroom. It is commercially cultivated on a mixture of raw cotton waste and rice bran and harvested in the button or egg stage before the pileus emerges. In the wild, the fungus tends to grow on decaying vegetation and wood.
Oyster Mushroom (Pleurotus ostreatus, P. sajor-caju) is a saprobic fungus that can commonly be found, growing on dead trees, in nature. This large white, gray-brown or ivory-colored mushroom is named for its oyster shell-like shape. Its cap can grow to around 5-15 cm in its longest dimension. It has white gills running down a very short, off-center short and white stalk.
Wood Ear (Auricularia polytricha) The earliest record of this species dated back to about 200-300 BC. It is now cultivated throughout the South Pacific and Asia. It has a common name that refers to the ear-shaped structure of the fruiting body. Mu-Er (wood ear) in China, and Pepiao (ear) in Hawaii. The fruiting bodies are usually brownish to reddish brown and has a consistency of jelly. In nature, the two species are saprobes that grow on tree logs. The cultivation of these species is the same as that of the Shiitake Mushroom. It is cultivated on logs and also on a mixture of saw dust and cotton waste.
Tremella fuciformis commonly known as 'Jelly Fungi' because of its gelatinous, jelly-like nature of the basidiocarps which are wrinkled or consist of leaf-like folds, also known as 'silver ear' or 'snow ear' fungus, widely eaten in the east. It is a saprophyte growing on decaying branches. This species produces a white, lobed, irregularly shaped fruiting body. It is also used in many Chinese delicacy. The method of cultivation of this species is identical to that of the Shiitake and Auricularia since it is a wood inhabiting species.
Wild edible fungi add flavour to ordinary staple foods but also valuable foods in their own right. Local names for termite mushrooms (Termitomyces ) reflect local beliefs that they are a fair substitute for meat and are confirmed by nutritional analyses. Not all wild edible fungi have such high protein content but they are of comparable nutritional value to many vegetables.
Ganoderma is not a palatable mushroom. It can be used to make tea or soup. It is a large, hard and leathery fungus with sessile or stalked basidiocarps, the undersurface of the basidiocarp is characterised by the presence of many tiny pores. It is one of the most respected ingredients in traditional oriental medicine. It is cultivated for its medicinal and tonic values.
Morchella esculenta, M. rotunda also known as ‘morel’ resemble mushrooms to the extent that they have a cap borne upon a central stem and known as truffles of the north but other popular names include sponge, pine cone, corncob, and honeycomb mushroom. Morels have delicate flavour are normally prepared by frying in butter and can be preserved. Morels are sought by thousands of enthusiasts every spring for their supreme taste and the joy of the hunt, and are highly prized by gourmet cooks, particularly in French cuisine. Like most edible fungi, they are also best when collected or bought fresh. One of the best and simplest ways to enjoy morels is by gently sautening them in butter, cracking pepper on top and sprinkling with salt. They are great additions to meat dishes or soups. However, as morels are known to contain thermolabile toxins, they must always be cooked before eating.
Besides these, ‘truffels’ (T. melanosporum) another highly prized gourmet mushrooms in the world. These fungi is actually mycorrhizal mushrooms differ from commonly produced saprotrophic types (such as shiitake and button mushrooms). Saprotrophic mushrooms live and feed on dead organic matter, whereas mycorrhizal mushrooms grow in a close, symbiotic (mutually beneficial) relationship with the living roots of a tree. Thus these mushrooms are difficult to produce artificially and that’s why these are much more costly than common button/shiitake mushroom and highly prized food. French gourmet Jean Anthelme Brillat-Savarin called truffles "the diamond of the kitchen". Edible truffles are held in high esteem in French, Georgian, Greek, Italian, Croatian, Middle Eastern and Spanish cooking, as well as in international haute cuisine. The "white truffle" or "trifola d'Alba Madonna" ("Truffle of the White Mother" in Italian) (Tuber magnatum) is found mainly in theLanghe andMontferrat areas of thePiedmont region in northern Italy. Tuber magnatum truffles sold for between $1000–$2200 per pound ($2000–$4500 per kg); as of December 2009 they were being sold at $14,203.50 per kilogram. The black truffle or black Périgord truffle (Tuber melanosporum), the second-most commercially valuable species, is named after thePérigord region in France and grows with oak and hazelnut trees.
Besides mushroom, fungal mycelium of Fusarium used as meat substitute after processing. ‘Quorn’ a commercial product of Fusarium sold as low-fat, low-calorie, cholesterol-free health food to consumers. Being used directly as food, fungi are also used in processing of various food products like soy-sauce using Aspergillus oryzae and A. sojae, Indonesian ‘temph’ using Rhizopus oligosporus.
In India, only button and oyster mushrooms are grown commercially. Lion’s share of cultivation is button mushroom. Large units with button mushroom production (capacity of 2000 – 3000 ton per annum) have been set up mostly for export purpose in southern, western and northern regions of the country. The national annual production is estimated to be around 50,000 ton of which 85% is button mushrooms. Besides, a large number of small units without climatic control equipment exist throughout India and function during the autumn and winter months only. At present India produces annually 10,000 tons of oyster mushroom. The quantity of oyster mushrooms exported by India is almost negligible in compare to the world. It is popularly grown in the states of Orissa, Karnataka, Maharashtra, Andhra Pradesh, Madhya Pradesh, West Bengal and in the North-Eastern States of Meghalaya, Tripura Manipur, Mizoram and Assam. In India particularly in north- eastern region fungi are highly coveted food. Study revealed more than 12 ethnic groups of Nagaland use 13 species and ethnic tribes in Assam use at least 7 species of mushroom for their livelihood. Climate of NE region is suitable for diverse group of edible fungi as evidenced by huge diversity available in the region. However, most of the edible fungi are collected from forest. There exist a good sign for commercial cultivation following GAP guidelines for export and domestic consumption.
About Author / Additional Info:
Senior Scientist working at ICAR-NRRI, India