Lactic Acid

Lactic acid is produced as the result of the oxidation of glucose to two molecules of pyruvate then pyruvate to lactate. Lactic acid can spoil food but also can increase the shelf life of foods such as cheese, yogurt, pickles and sauerkraut. The lactic acid bacteria provide protection against spoilage by producing natural bacteroicins (substances that kill bacteria). Because of this action, the use of lactic acid bacteria is being studied as a preservative. The following information from "Lactic Acid Bacteria as Food Preservatives" by Yali Friedman describes some of the benefits of lactic acid and some information on fermentation:
 
There are three main conditions for an optimal lactic acid fermentation:
  • Addition of a sufficient amount of fermentable carbohydrates;
  • Reduced pO2 during the fermentation process and storage of the fermented product.
  • Rapid multiplication of the starter culture and sufficient production of lactic acid.

The bacteriocins produced by lactic acid bacteria have gained much attention as potentially useful food additives against food-borne pathogens.

One bacteriocin, nisin was the first bacteriocin derived from fermentation of a lactic-acid bacterium and was approved by the FDA in April 1989 to prevent the growth of botulism spores in pasteurized process-cheese spreads. Nisin does not inhibit Gram-negative organisms, yeasts or fungi, but does inhibit most Gram-positive organisms including spore-formers such as Clostridia botulinum and heat-resistant spoilage organisms.

Lactic acid bacteria and their byproducts are currently present in many of the foods we consume. For this reason, they are regarded as safe and natural by consumers. Metabolic byproducts of lactic acid bacteria have been shown to inhibit the growth of several important pathogens, and increase shelf life beyond current "chemical" preservatives. Because lactic acid bacteria already preserve foods such as cheese and milk, it makes sense to try and inoculate them into other foods as well.

Besides being less potentially toxic or carcinogenic than current antimicrobial agents, lactic acid bacteria and their byproducts have been shown to be more effective and flexible in several applications.

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