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Foods -- General

Do you have any background about acids used in food preparation?

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Yes. We sometimes use the terms "pH" and "percent acidity" interchangeably, but technically they are different measures. There is no direct correlation between these measures other than that both assess the level of acidity. I have prepared a very brief overview of acids and what the two above-mentioned measures mean. Nearly 100% of the time, in food safety, we are concerned with the pH. In fact, the only instance in which we would use percent acidity in consumer food safety work is to determine if commercially prepared vinegar is safe to use as an acidifier of pickled products. One must use a product that is labeled 5% acidity or higher. Acids are substances that dissolve in water, releasing hydrogen ions. The strength of an acid depends on its ability to release hydrogen ions - a strong acid having a marked tendency and a weak acid a weak tendency. The pH of an acid is in the range of 0 to 7; the pH of an alkali is in the range of 7 to 14. Nearly all foods have a pH of less than or equal to 7, which is why foods are classified as high acid or low acid and not as alkaline. Acids have a sour taste and alkalies have a bitter taste. All acids found in foods are weak organic acids. Therefore they cannot release hydrogen ions as readily as can strong acids. Examples of strong acids: hydrochloric acid (which is found in gastric juice), sulfuric acid, and nitric acid. Examples of acids and the foods in which they are found: Acetic acid - found in vinegar; Ascorbic acid (Vitamin C) - fresh fruits and vegetables; Citric acid - citrus fruits; Lactic acid - sour milk, yogurt; Malic acid - apples, cherries; Oxalic acid - spinach, rhubarb; Tartaric acid - grapes. There are two common measures of acidity: pH and percent acidity. PH is a measure of the acidity or alkalinity of a solution, based on the concentration of released hydrogen ions found in the solution. The concentration of acid or percent acidity is the amount of all the acid in a solution, not just the released hydrogen ions. In food microbiology, we use pH to determine the conditions in which microorganisms cannot grow in a food. For instance, in home canning, C. botulinum cannot grow in products that have a pH (naturally or through the addition of an acid) of less than or equal to 4.6.

PREPARED BY: Angela M. Fraser, Ph.D., Associate Professor/Food Safety Specialist, and Carolyn J. Lackey, Ph.D., R.D., L.D.N., Professor/Food and Nutrition Specialist, North Carolina State University. (August 2004)

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