**2.3.1 Nutritional importance**

Man has constantly realized the nutritional value of mushrooms, as well as their healthy properties compared to other foods, such as red meat, where mushrooms are more advantageous and important as they are great sources of carbohydrates, proteins, mineral salts, vitamins and essential amino acids, which can help to maintain a good nutritional balance (Crisan and Sands, 1978; Garcia et al., 1993; Miles and Chang, 1997).

Nutritional Analyses of mushrooms have shown their importance. They contain more protein than vegetables. Sources of protein such as meat, chicken, have a high level of cholesterol and fat, which are known to cause increase in weight and cardiovascular diseases. For this reason, the proteins from other sources became more popular in recent years, such as proteins from fungi, algae, bacteria and yeast (Lajolo, 1970; Chang and Haynes, 1978; Urben et al., 2003).

Studies carried out by Lintzel (1941; 1943), according to Crisan and Sands (1978), indicated that approximately 200 g of mushrooms (dry weight) are sufficient to feed a normal human being weighing approximately 70 Kg, providing a good nutritional balance. Nutritionally, these macrofungi are a good food source. The composition of fats, carbohydrates, vitamins, etc., varies according to species, the cultivation method and also with the substrate used in cultivation (Crisan and Sands, 1978; Przybylowicz and Donoguue, 1990; Bononi et al. 1999; Miles and Chang, 1997; Andrade, 2007).

Mushrooms are excellent foods for the diets, because they nourish and do not accumulate fat in the organism. They are sources of all essential and some nonessential amino acids. They contain minerals like calcium, potassium, iodine, phosphorus and vitamins including thiamine, riboflavin, niacin, and ascorbic acid, and others related to the B complex (Molena, 1986; Miles and Chang, 1997 Bononi et al., 1999). They also have a high unsaturated fat content (Miles and Chang, 1997).

Mushrooms with larger nutrition index (based on essential amino acid index) have nutritional value similar to meat and milk, while those with a smaller nutrition index compare to some vegetables such as carrots and tomatoes. The nutritional index of these fungi outperforms those of plants and vegetables, except soy (Crisan and Sands, 1978). In general, the protein content of fresh mushrooms is twice higher than cabbage, four times greater than the content of protein of the orange and twelve times that of the Apple (Chang, 1980).

Research carried out in India by Garcia, et al. (1993), where the authors compared the nutritional levels of *Agaricus* and *Pleutotus*, revealed the importance of the amino acids of these mushrooms for people that are lacking animal protein, for religious reasons, and whose main food source comes from vegetables and grains usually poor in essential amino acids. Food supplementation with mushrooms is of fundamental importance in the diet of this kind of people.

In addition, there is also a great interest in the cultivation of the mycelium in a submerged condition to obtain flavoring and fragrant compounds of great value to the food industry. For this purpose, the mycelium is grown submerged, using a variety of substrates, according to the type of the desired compound. This flavoring property is characteristic of some lignolitic mushrooms, such as the *Pleurotus* genus (Gurtiérrez et al., 1994)
