Effects of Selected Food Additives on Growth of Pseudomonas fragi

Tests were made of inhibition of Pseudomonas fragi in lactose-yeast extract broth by the food additives Chlortetracycline, nisin, bacitracin, chloramphenieol, lysozyme, ethylenediaminetetraacetie acid (EDTA), nitrofurazone, propyl-p-hydroxybenzoate, sodium benzoate, and potassium sorbate.The additives that proved effective in broth were tested in skimmilk and halfand-half.Nisin, baeitracin, lysozyme, and nitrofnrazone were ineffective in broth; chloramphenicol increased the lag period prior to development of turbidity but resulted in ehloramphenicol-resistant populations; and EDTA inhibited the organism slightly in broth but not in skimmilk or half-and-half.Propyl-p-hydroxybenzoate, chlortetracycline, and a mkxture of lysozyme and EDTA were effective in broth but not in skimmilk or half-and-half, a difference attributed to metal ions in dairy products that react with chlortetracycline and EDTA.Sodium benzoate retarded P. fragi in broth, but only at low pit.Potassium sorbate was ineffective at pH 6.5 in broth, but at pit 5.5 and 5.2 inhibited growth of P. fragi in broth, skimmilk, and half-and-half.Food spoilage can occur from either chemical reactions of food constituents, often involving enzymes naturally present in food, or chemical changes brought about by enzymes produced by microorganisms growing in food.Spoilage from microorganisms can be delayed or prevented by killing undesired microorganisms before they grow extensively or by making the environment unsuitable for their growth.~'iilk and fresh milk products are normally refrigerated, and their spoilage usually results from microorganisms, often called psychrophiles, capable of growing more rapidly than most microorganisms in milk at refrigeration temperatures.These organisms produce such defects as ropiness, putrid or fruity odor, and bitter or rancid flavor in a variety of dairy and nondairy products.Since they are sensi-