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Acid value
In chemistry, acid value (AV, acid number, neutralization number or acidity) is a number used to quantify the acidity of a given chemical substance. It is the quantity of base (usually potassium hydroxide (KOH)), expressed as milligrams of KOH required to neutralize the acidic constituents in 1 gram of a sample.[1][2][3][4] The acid value measures the acidity of water-insoluble substances like oils, fats, waxes and resins, which do not have a pH value.
The acid number is a measure of the number of carboxylic acid groups (−C(=O)OH) in a chemical compound, such as a fatty acid, or in a mixture of compounds.[2] In other words, it is a measure of free fatty acids (FFAs) present in a substance. In a typical procedure, a known amount of sample dissolved in an organic solvent (often isopropanol) and titrated with a solution of alcoholic potassium hydroxide (KOH) of known concentration using phenolphthalein as a colour indicator.[2] The acid number for an oil sample is indicative of the age of the oil and can be used to determine when the oil must be changed.[5]
A liquid fat sample combined with neutralized 95% ethanol is titrated with standardized sodium hydroxide of 0.1 eq/L normality to a phenolphthalein endpoint. The volume and normality of the sodium hydroxide are used, along with the weight of the sample, to calculate the free fatty acid value.[3]
Acid value is usually measured as milligrams of KOH per gram of sample (mg KOH/g fat/oil), or grams of KOH per gram of sample (g KOH/g fat/oil).[5]
- ^ "14.10.1: Foods- Acid Value and the Quality of Fats and Oils". Chemistry LibreTexts. May 26, 2016. Retrieved October 28, 2022.
- ^ a b c Ahuja, Satinder (January 25, 2015). Food, Energy, and Water: The Chemistry Connection. Elsevier. p. 301. ISBN 9780128003749. OCLC 900781294.
- ^ a b Nielsen, S. Suzanne (March 20, 2010). Food Analysis Laboratory Manual, 2nd Edition. Springer Science & Business Media. pp. 108–109. ISBN 9781441914637. OCLC 663096771.
- ^ O'Brien, Richard D. (December 5, 2008). Fats and Oils: Formulating and Processing for Applications, 3rd Edition. CRC Press. pp. 220–221. ISBN 9781420061673. OCLC 367589246.
- ^ a b Cite error: The named reference
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