Although mushrooms have at one time been used as a staple food in some parts of Russia and South America, and they have been served as the main dish during mushroom seasons in Africa, they are generally considered only as an ingredient or complement to various dishes-rather than as a daily vegetable. However, mushrooms have been and will be increasing in importance as a source of food because they have a pleasing flavor, fine texture, adequate protein content (Crisan and Sands 1978), and health benefits (Mori 1974). The demand for mushrooms in some industrialized countries has increased threefold during the period 1965-1975 (Delcaire 1978). As people become wealthier, their consumption of mush-rooms increases. In 1977, the total per capita consumption of Agaricus mush-rooms in West Germany was about 12 times that of the world average. It is hoped that in the near future mushrooms can be cultivated widely just as other common vegetables are.
虽然蘑菇在同一时间都被用来作为俄罗斯和南美一些地区的主食，并已在非洲的蘑菇季节期间作为主盘供应，他们通常被认为只能作为一种成分或补充各种菜肴而不是作为日常的蔬菜。然而，蘑菇已被作为食物来源的重要性将越来越大，因为他们有一个可喜的味道，质地细腻，足够的蛋白质含量（克里桑和金沙1978年），以及健康的好处（森，1974）。 1965年至1975年期间，（Delcaire1978），蘑菇在一些工业化国家的需求增长了三倍。随着人们越来越富裕，他们的消费增加的蘑菇房。 1977年，在西德的人均总消费的双孢蘑菇的客房，是世界平均水平的12倍左右。希望在不久的将来蘑菇可以广泛种植其他常见的蔬菜。

WHAT ARE MUSHROOMS?
Mushrooms belong to the group of organisms known as filamentous fungi. Be-cause all fungi lack chlorophyll, they cannot get their energy, as green plants do, directly from the sun. They must obtain their nutrients from waste products or other living things. The word mush-room may mean different things in various countries. In this article, the com-pound term edible mushrooms refers to both epigeous and hypogeous fruiting bodies of macroscopic fungi that are al-ready commercially cultivated or grown in "half-culture"' processes or grown under controlled conditions. Only about 25 species of more than 2000 edible fungi are widely accepted as human food, and only a few of these are commercially cultivated or grown in half-culture processes. With technical advances during the past few decades, the cultivation of edible mushrooms has spread all over the world. The total world production of 10 kinds of commercially cultivated mushrooms was estimated to be 916 thousand tons in 1975 (Delcaire 1978).
The four most important mushrooms are the commonly cultivated white mushroom/button mushroom (Agaricus bisporus), the black forest mushroom/ shiitake (Lentinus edodes), the straw mushroom (Volvariella volvacea), and oyster mushrooms (Pleurotus sp.). Their yield and distribution are shown in Figure 1. Although Agaricus is the main edible mushroom in Europe and the United States, it is cultivated in 72 countries. Japan is now the world's largest producer of Lentinus. Volvariella is familiar to all Southeast Asian countries, although China is the main producer. Pleurotus is also important, though its status is questionable because some people in Europe develop allergies to its spores. No such cases have been reported among Asians.
FOOD VALUE OF MUSHROOMS
The average dry-matter content of the four kinds of mushrooms is shown in Table 1. Fresh mushrooms generally contain between 85-92% moisture, which is not unusually high when mush-rooms are compared with common vegetables like Chinese cabbage (94.2%). There are considerable variations of moisture content within a species. This may be due to the environmental conditions under which they are grown and harvested.
Table 1 also shows the comparative protein percentages for the four kinds of mushrooms calculated on wet basis. The Lentinus mushroom has a lower protein content than the other three, which are grown under different climates and nutritive conditions. In general, the protein content of fresh mushrooms is about twice that of vegetables such as asparagus and cabbage and 4 times and 12 times that of fruits such as oranges and apples, respectively.
A comparison of the amino acid con-tent of these four edible mushrooms is given in Table 2. They are generally very similar. The amino acids varying the most are lysine, glutamic acid, and histidine. The lysine average for Agaricus is almost the same as that of Volvariella but is almost twice that of Pleurotus and three times that of Lentinus. But Lentinus has a much higher glutamic acid content. All the mushroom proteins contain all nine amino acids essential for man, and they are especially rich in lysine and leucine, which are lacking in most staple cereal foods. However, there are low amounts methionine and cystine, both of which are essential and abundant in meat protein.
Mushrooms are also a good source of the following individual nutrients: fat, phosphorus, iron, thiamine (vitamin B 1), riboflavin (vitamin B2), and niacin. They are low in calories, carbohydrates, and calcium, and Agaricus is high in ascorbic acid (vitamin C) and Lentinus is high in ergosterine (vitamin D). But they are all devoid of vitamin A activity. The overall nutritive value is intermediate between low-grade vegetables and high-grade meats (see Table 3). The high value is close to that of milk on the basis of essential amino acid indexes and amino acid scores.
Mushrooms, like other fast-growing microorganisms, contain higher amounts of nucleic acid than do conventional foods (see Table 4). The nucleic acid ranges from 3 to 25% in microorganisms, 1.1 to 4% in cereals, and 2.2 to 5.7% in meats and fish. The Protein Advisory Group of the United Nations System (PAG 1970) suggested that a daily maxi-mum of 4 g nucleic acid, of which 2 g are obtained from microorganisms, represents a safe practical limit for most adult populations. As shown in Table 4, the average content of nucleic acids in the edible mushrooms is about 7.1%. On this basis, it is quite safe for one to consume as much as 300 g of fresh mushrooms daily. Since this is generally beyond the human daily consumption, the content of nucleic acid in edible mushrooms should not limit their use as a daily vegetable.
MUSHROOM FOOD FOR THE FUTURE
In view of current energy, food, and population problems, food and feed will have to be produced from waste materials on a massive scale within a few decades. Recently, many aspects of food protein production from wastes by yeast, algae, and bacteria have been considered (Birch et al. 1976, Tannenbaum and Wang 1975). Mushrooms and other macromycetes, the microbial foods used longest by man, can also flourish successfully on a wide variety of in-expensive substrates/wastes, such as cereal straws, banana leaves, sawdusts, and cotton wastes from textile factories. Cellulose, hemicellulose, and lignin are the main components of these wastes and are most resistant to biological degradation. However, mushrooms and a few other closely related organisms possess the enzyme complexes which en-able them to attack and degrade these manufacturing by-products.
The world production of straw in 1977 was estimated to be 2325 million tons (see Table 5), but no one knows how all this straw is being used. In 1974, for ex-ample, nearly 60% of the straw produced in the eastern region of England was burnt in the field, 25% was used as bed-ding, and 0.1% was ploughed into the soil (Seal and Eggins 1976). In the United States, rice straw is generally burnt in the field, too (Kurtzman 1976). In other countries, the wastefulness is similar. If the amount of straw burnt in the field could be properly used to grow mush-rooms, a millon tons of mushrooms for table use would be produced, and mil-lions of tons of organic fertilizers from the spent mushroom composts would be provided to the local farmers.
The techniques used for the cultivation of edible mushrooms are derived from the disciplines of microbiology and environmental engineering. They can be applied as a kind of primitive farming in rural areas or as a high technology industry in metropolitan suburbs. A book on the cultivation of the 12 best known species of edible mushrooms is available (Chang and Hayes 1978). It contains useful information about the food value, improvement of quality, yield, and economics involved in cultivating mushrooms.
The term biological efficiency was recently introduced to the mushroom industry (Tschierpe and Hartman 1977) to express the yield of mushrooms as a pro-portion of the dry weight of compost at spawning. A 100% biological efficiency is attainable in several edible mush-rooms-e.g., Agaricus and Pleurotus-- within 30-45 days. This means that one kilogram of fresh mushrooms can be harvested in 30-45 days from two to four flushes grown on one kilogram of dry compost material. This has been achieved often under experimental conditions and sometimes under commercial auspices. At present, an experienced mushroom grower obtains a biological efficiency of 60-75% during the year. To achieve a 100% biological efficiency seems to be a reasonable goal for the mushroom industry in the years ahead. However, even at 65% biological efficiency, if only one-fourth of the world's annual yield of straw (2325 million tons) were used to grow mushrooms, about 377.8 million tons of fresh mushrooms could be produced. Such an amount would provide 4103 million people (FAO Production Yearbook 1977) with 250 g of fresh mushrooms daily.
Cultivation of some undomesticated species of edible mushrooms has been studied in the laboratory (Delmas 1978). Industrial cultivation of some of these species may be feasible. By use of various species, mushrooms can be grown in tropical, subtropical, and temperate climates. And when one considers that they can be produced on waste materials-converting products of little or no market value into food for an over-populated world-then there is no doubt that mushrooms represent one of the world's greatest untapped resources of nutritious and palatable food for the future