Q. Which Foods are used by Microorganisms for Energy?

The carbohydrates, especially the sugars, are most commonly used as an energy source, but other carbon compounds can also serve the purpose, e.g., esters, alcohols, peptides, amino acids and organic acids. Microorganisms differ in their ability to use some of the simpler soluble sugars. Many organisms cannot use the disaccharide lactose (milk sugar) and therefore do not grow well in milk. Some yeast does not attack maltose. Most organisms, if they utilize sugars at all, can use glucose. The ability of microorganisms to hydrolyze pectin, which is characteristic of some kinds of bacteria and molds, is important in the softening or rotting of fruits and vegetables or fermented products. The ability to synthesize amylolytic (starch degrading) enzymes will favour the growth of an organism on cereals and other starchy products. The addition of fruits rich in sucrose and other sugars to yoghurt increases the range of carbohydrates availability and allows the development of a more diverse spoilage microflora of yeasts. Bacteria differ in their ability to utilize different foods as a source of energy. Some can use a variety of carbohydrates, e.g., the coliform bacteria and Clostridium spp., and others only one or two. Some can use other carbon compounds like organic acids and their salts, alcohols, and esters (Pseudomonas spp.).