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Effects of Chemical properties on Spoilage

	Effects of Chemical properties on Spoilage - The chemical properties of a food product influence the type of microorganisms that can grow, and hence determine the changes in appearance, flavour, odour, and other qualities of food. Composition: Proteins are degraded by proteolytic organisms. Many bacterial species, especially spore formers, gram negative rods such as Pseudomonas and Proteus, and a few cocci can attack proteins. Mould spoilage is also common.
Carbohydrate foods are spoiled by carbohydrate fermenting. microorganisms, particularly by yeast and moulds. Bacterial species of the genera Streptococcus, Leuconostoc and Micrococcus are saccharolytic and can also attack carbohydrates. Fats are digested by relatively few microorganisms, mainly moulds and few gram negative bacteria. Fats undergo hydrolytic decomposition and become rancid l1S malodorous fatty acids are set free. Acidity: The reaction of nearly a1l foods is below pH 7.0. Foods are classified as acid or nonacid. The reaction of acid food is below pH 4.5, and that of nonacid food above pH 4.5. Most fruits are acid foods, while nearly all vegetables, fish, meats, and milk products are nonacid.
Acid foods have sufficiently low pH and, therefore, prevent the growth almost bacterial species. They are spoiled mainly by yeast and moulds. Nonacid foods are particularly subject to bacterial spoilage, but will also support growth of moulds under proper conditions. Moisture and osmotic pressure: Growth of microorganisms require at least 13 per cent free water in foods, Moulds require the least free water and bacteria require the most. Foods of high sugar and salt concentration do not, support the growth of most microorganism). Bacteria are generally inhibited (by 5 to 11 percent salt, whereas many moulds and some yeasts can tolerate salt concentrations greater than 15 percent.
Sixty five to seventy percent sugar is required to inhibit moulds; 50 percent inhibits bacteria and most yeasts. Foods of high sugar or salt content are therefore most likely to be spoiled by moulds. Table 5.2 summarizes the influence of the chemical properties of food on the type of microorganisms that can grow and hence determine the nature of the spoilage process.

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