What are Fungi?

• Fungi have no chlorophyll and their body is not differentiated into parts like the root, stem, leaves, and flowers.

  • However, compared to bacteria fungi are more highly evolved (eukaryotes, with a true nucleus) and multicellular.

General Study of Fungi:

• The most common fungi are the molds that grow on our food, bread, fruit, and even on leather and on the bark of trees.

  • Mushrooms and toadstools are a common sight in the warm, rainy season.

    • Most mushrooms are poisonous but some are edible.

Molds:

• Rhizopus is the common bread mold.

  • It grows not only on bread but also on a variety of other organic matter such as fruit, animal dung, and leather goods, in warm and humid climates.

    • It consists of a network of transparent thread-like structures called hyphae and the entire mass of these threads is called mycelium.

      • The penetrating hyphae secrete certain enzymes which digest the food in the bread substratum (extracellular digestion) and absorb it.

• Reproduction in bread mold is both asexual and sexual.

  • Asexual reproduction starts within a few days of the growth of the mycelium.

    • Some hyphae become erect (sporangiophores) and swell up at their tips.

    • The swollen tip is called sporangium which turns dark as the spores inside get matured.

• The sporangium bursts to liberate spores which are scattered by the wind.

  • Falling on a suitable substratum the spores germinate if there is suitable warmth and moisture, and form a new mycelium.

Yeast:

• Yeasts are generally in the form of separate

  spherical cells.

  • There are several species of yeast under the genus Saccharomyces.

    • All yeasts are one-celled fungi.

      • They occur either singly or in the form of budding chains.

• Occurrence:

  • Yeasts are found freely in the atmosphere.

    • They readily grow in all kinds of sugary solutions and in any plant exudations containing sugar.

    • They grow readily on grapes, in the nectar of flowers, in sugar cane juice, etc.

• Structure:

  • The yeast cell is ovoid in shape and has a distinct cell wall and a nucleus.

  • There may be one or more vacuoles in the cytoplasm.

• Nutrition:

  • Yeast cells can directly absorb simple sugar (glucose) but the cane sugar or sucrose has to be first broken into simple sugar by one of the enzymes before absorption into the cell.

• Respiration:

  • Yeast respires anaerobically in the absence of air, i.e. without using oxygen.

Economic Importance of Yeast:

• Yeast’s greatest importance to mankind is through its property of alcoholic fermentation.

• The alcohol (ethanol) produced is of great commercial importance.

  • When produced for beverages, the quality of alcohol varies with the material fermented but also with the kind of yeast employed.

Importance of Fungi:

• Several species of Penicillium are used in processing fine-flavored cheeses.

• One of its species Penicillium notatum is most notable as the source of the first wonder drug antibiotic penicillin (discovered by Alexander Fleming).

Harmful Fungi:

• Most fungi are harmful.

  • They spoil food.

  • Many cause damage to forest trees.

• Penicillium and Aspergillus are two commonly popularly called blue and green mold rest.

  • They grow on oranges, lemons, and other items.

  • There are some fungi that cause diseases such as ringworm.

• Next time you happen to see a greenish growing on the outer skins of overripe/rotting lemons, be sure it is some species of Penicillium.

Useful Role of Fungi:

• An antibiotic is a chemical substance produced by a living microorganism that can stop the growth of or kill other microorganisms.

  • The first antibiotic was penicillin produced by a mold.

Criteria for Good Antibiotics:

• It should be able to kill a variety of disease-producing microorganisms (“broad spectrum” antibiotics).

• It should not produce undesirable side effects.

• It should not kill normal bacteria in the host.

Other Uses of Antibiotics:

• As food preservatives, especially for fresh meat and fish.

• For treating animal feed.

• For controlling plant pathogens.

Importance of Fungi (Industry):

• Wine and other alcoholic beverages like beer are the products of the process called fermentation.

  • Fermentation is a process in which the micro-organisms (yeast and bacteria) break down carbohydrates into simpler products (ethanol or lactic acid) in the absence of oxygen.

• The source used for making wine is grape and for beer, it is barley maltose, and the micro-organism employed in yeast (Saccharomyces cerevisiae).

  • Grapes are crushed and fermented in large vessels.

    • Yeast cells that may be naturally present in the grapes or added carry out the process.

    • Ethanol (ethyl alcohol) is produced at a concentration of about 12%, and this concentration starts killing yeast cells.

• Spirits such as whisky and gin, which have a much higher alcohol content, are obtained by distillation of the fermented mixture.

Characteristics of wine:

• Wine is quickly absorbed into the body.

• In very mild quantities it may be a stimulant but when consumed in large quantities it is harmful in many ways.

• The alcoholic may develop body ailments, particularly liver cirrhosis

Baking (Bread-Making):

• In baking a mixture of flour (atta or maida), some fat, salt, and water are required to make “dough”, the starch of the flour gets converted into sugar.

• When the yeast is added, it ferments the sugar and produces carbon dioxide, and the dough “rises” (leavening) to about three times its original volume.

• When the dough is baked the gas bubbles expand and give the bread a light “spongy” texture.

Cheese:

• Cheese is a valuable food with high quantities of protein, some fat, together with calcium and phosphorus, and vitamin A with some quantities of vitamin B.

• People have been eating cheese for centuries. It has been made from milk. The manufacture of cheese includes the following major steps:

  • Curdling of milk by addition of lactic acid bacteria (Lactobacillus).

    • Curd produced is separated from the whey.

  • Curd is processed to remove moisture.

    • At this stage, it is called cottage cheese.

  • Salting: This further removes moisture, and prevents the growth of undesirable micro-organisms.

  • Ripening: The curd is kept at a suitable temperature and humidity.

    • The micro-organisms added along with lactic acid bacteria at step 1, impart particular flavors to the cheese.

Mushroom Cultivation:

• Mushrooms are of various shapes and sizes.

  • Many have a cap and stalk, but in some varieties stalk is absent.

    • There are a large number of mushroom species that grow wild in nature.

• Not all mushrooms are edible.

  • In fact, most are mildly or severely poisonous.

    • The edible ones have been eaten by humans since ancient times.

• Agaricus bisporous is the most common edible mushroom eaten practically all over the world.

  • At present, three kinds of mushrooms are widely cultivated in India and abroad:

    • White button mushroom (Agaricus bisporous).

    • Paddy straw mushroom {Volvariella).

    • Oyster mushroom (Pleurotus).

• Mushroom cultivation is done indoors and hence a little land area is required.

  • Mushrooms can be grown on substrate or compost based on various agricultural wastes which in turn are recycled [Compost: decayed organic matter used for fertilizing land].

• White button mushroom (Agaricus bisporous is the most popular variety grown in India.

  • Its cultivation involves five major steps:

    • Composting:

      • The compost is prepared by

        mixing the following in certain proportions.

      • Wheat or paddy straw

      • Chicken manure

      • Some organic and inorganic fertilizers.

        • The compost is kept at about 50°C for about one week.

    • Spawning:

      • “mushroom seed” consisting of mycelium of the selected type of mushroom is introduced into the compost and allowed to spread for a couple of days.

    • Casing:

      • A thin layer of soil is spread over the compost.

        • This is a very important step.

      • It gives support to the mushroom.

      • It provides humidity

      • It prevents quick drying of the compost.

      • It helps to regulate temperature.

    • Cropping and Harvesting:

      • The growth occurs in three principal stages:

        • Mycelium (a network of fibrous mass) grows within 2 to 6 weeks.

        • Tiny pin heads.

        • Button stage which grows bigger attaining marketable size.

      • The full-grown mushrooms are taken out.

    • Preservation:

      • Mushrooms are highly perishable.

      • Their shelf life is increased by a variety of processes:

        • Vacuum cooling

        • Giving gamma radiation & storing at 15'C.

• Nutritive value of mushrooms:

  • Mushrooms are excellent sources of vitamins and minerals.

  • They contain a good amount of niacin, pantothenic acid, and biotin.

  • The vitamins in mushrooms are well retained during cooking, canning, and dehydration.

    • Fresh mushroom contains about 85—95% moisture, 3% protein, 4% carbohydrate, 0-3—0 4% fat, and 1% minerals and vitamins