Moulds are multicellular filamentous fungi. They grow on foods with their fuzzy or cottony appearance, sometimes coloured. Moulds are larger and more complex in structure than bacteria or yeast. Moulds are made up of mycelium and spores. They grow in a network of hair like fibres called mycelia and send up fruiting bodies that yield spores. Some of common moulds are Aspergillus, Penicillium, Rhizopus and Heliminthosporium. Usually a moldy or mildewed food is considered unfit to eat.
They thrive best in closed, damp and dark situation and require adequate supply of warmth, moisture and air for growth. They are strictly aerobic in nature and require less available moisture than yeast and bacteria and can grow well at 25-30°C. Moulds prefer sugar containing substances like jam, jelly, preserves and other sweet products. They can grow at wide range of pH (2 to 8.5) but majority grow well at acidic pH. Therefore, they grow nicely on pickles, juices etc. They can grow on many kind of foods especially when temperature, air and humidity are favourable. Their growth can be seen only on the surface of food . Majority of moulds are sensitive to heat and are destroyed at 60°C when heated for 30 minutes. Boiling quickly destroys both moulds and their spores.
They not only consume nutrients present in food thereby lowering the food value but also produce odd by-products, which spoil the flavour, taste and texture of food hence change the quality contents of the entire product. Some moulds produce toxic substances known as mycotoxins. For example Aspergillus flavus produces aflatoxins in moist groundnuts.
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