Q. Accessory Food Substances or Vitamins ?
Bacteria also vary in their need for vitamins or accessory growth factors. Some microorganisms are unable to synthesize some or all of the vitamins needed for their growth. For example, Staphylococcus aureus synthesizes part while Pseudomonas or Escherichia coli all of the factors needed. The lactics and many pathogens must have all of the vitamins furnished.
Microorganisms may require B vitamins in low quantities and most of the natural foods have an abundant quantity of these. Gram positive bacteria are the least synthetic and must, therefore, be supplied with one or more of these compounds before they will grow. Gram-negative bacteria and molds are able to synthesize most of their requirements. Consequently, these two groups of organisms may be found growing on foods low in B vitamins. Fruits tend to be lower in B vitamins than meats. Thus, the usual spoilage of fruits is by molds rather than bacteria since fruits also have a low pH and positive Eh, which favour mold growth.
Egg white contains biotin but also contains avidin, which ties it up, making it unavailable to microorganisms and thus eliminate spoilage of eggs through biotin requiring organisms. The processing of foods often reduces the vitamin content. For example, thiamine, pantothenic acid, folic acid and ascorbic acid (in air) are heat-labile. Drying causes a loss in vitamins such as thiamine and ascorbic acid. Even storage of foods for long periods, especially if the storage temperature is elevated, may result in a decrease in the level of some of these growth factors.