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Organic Acids


 Updated 2015-08-15

 Organic Acids in Foods

Ambiguety  -  organic acids - fatty Acids

The term organic acid used in food composition and nutrition labelling is a somewhat ambiguous term with no actual well-formulated scientific definition except for meaning any acid belonging to the group of organic compounds.
The most common organic acids in foods are carboxylic acids, but also other compounds like sulfonic acids belong in this group.

Adding to the confusion is the fact that the fatty acids chemically also belong to a sub-group of the organic acids - the carboxylic acids.

Greenfield and Southgate mention organic acids in quite a few places, but gently avoids defining these organic compounds.

IUPAC defines fatty acids as "Aliphatic monocarboxylic acids derived from or contained in esterified form in an animal or vegetable fat, oil or wax. Natural fatty acids commonly have a chain of 4 to 28 carbons (usually unbranched and even-numbered), which may be saturated or unsaturated. By extension, the term is sometimes used to embrace all acyclic aliphatic carboxylic acids.” (see the IUPAC Gold Book )

Despite the fact that fatty acids chemically are a sub-group of organic acids, the terms fatty acids and organic acids are used as two separate terms in food composition and nutrition labelling - with a somewhat unclear borderline between the two groups.
This can be seen in the IUPAC definition’s extension, which include the very short chain carboxylic acids with 2 or 3 carbon atoms, and you may actually in scientific literature find these (acetic acid and propionic/propanoic acid) mentioned as both organic acids and fatty acids.

Normally, the fatty acids are defined by the organic acids that are determined in fatty acid analysis, i.e. fatty acids bound in triglycerides, phospholipids, etc., after esterification of the lipid extracted with an organic solvent.
The analytical method then determines the fatty acid group, usually carboxylic acids with 4 to 26 carbon atoms (the short chain fatty acids only being present in milk and milk products).

Other organic acids are determined with various different methods.

The organic acids

There are quite a lot of other “organic acids” (carboxylic acids), which are not necessarily “usually unbranched and even-numbered”.

The organic acids are present in a long range of foods, naturally especially fruits, berries and vegetables, but also in manufactured food products, where the acids are used naturally as ingredients to preserve the food or as food additives as preservatives, antioxidants, etc.
The organic acids may also be formed during the production of foods, e.g. during fermentation, and may be important in the formation of taste properties.

The organic acids are energy contributing components, and it is important to include their energy contribution in the calculation of a food's energy content.

Merrill and Watt list some of the important organic acids present in foods

  • malic
  • citric
  • isocitric
  • ascorbic
  • oxalic
  • lactic
  • succinic
  • acetic
  • quinic
  • tartaric
  • benzoic
  • glyoxalic
  • salicylic
  • aconic
  • melonic

To this list could be added

  • sorbic
  • aconitic
  • adipic
  • chlorogenic
  • diketogulonic
  • glycolic
  • etc.

A more comprehensive list of organic acids in foods are given in the EuroFIR Component thesaurus, see the EuroFIR thesauri .

It is worth noting that some of these organic acids are vitamins and/or used as food additives, e.g. antixodants or acidifiers (ascorbic acid, citric acid, etc.), which may make the handling of the organics acids in food composition or nutrition labelling somewhat complex.

Energy contribution of organic acids

The energy contribution of the organic acids is not neglible in a range of foods. Although varying between the different organic acids (the longer the chain of the molecule, the higher the heat of combustion is), the contribution of organic acids to the energy content of food has been settled to a fixed factor in nutrition labelling.

The Codex Alimentarius Commission’s Guidelines for Nutrition Labelling (CAC/GL 2-1985) defines an energy factor for organic acids of 13 kJ/g (3 kcal/g).

In agreement with Codex Alimentarius, the same factor is defined in the European Regulation (EU) No 1169/2011 of the European Parliament and of the Council of 25 October 2011 on the provision of food information to consumers as well as in the nutrition labelling regulation in a range of countries around the world.
 


 References

  • IUPAC.
    Compendium of Chemical Terminology, 2nd ed. (the "Gold Book").
    Compiled by A. D. McNaught and A. Wilkinson.
    Blackwell Scientific Publications, Oxford (1997).
    XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins.
    ISBN 0-9678550-9-8. doi:10.1351/goldbook.
    Last update: 2012-08-19; version: 2.3.2.
    DOI of this term: doi:10.1351/goldbook.F02330.
     
  • Merrill A.L. and Watt, B.K.:
    Energy Value of Foods … basis and derivation.
    Agriculture Handbook No. 74, revised February 1973.
    Human Nutrition Research Branch, Agricultural Research Service, United States Department of Agriculture.
     
  • EuroFIR AISBL:
    The EuroFIR Thesauri - Component thesaurus
    EuroFIR AISBL website accessed 2014-02-22
     
  • Codex Alimentarius Commission:
    Codex Guidelines for Nutritional Labelling. CAC/GL 2 – 1985 (Adopted 1985. Revisions 1993 and 2011. Amendment 2003, 2006, 2009, 2010, 2012 and 2013. Annex adopted 2011 and revised 2013).
    Joint FAO/WHO Food Standards Programme, FAO, Rome 2013.
     
  • Regulation (EU) No 1169/2011 of the European Parliament and of the Council of 25 October 2011 on the provision of food information to consumers, amending Regulations (EC) No 1924/2006 and (EC) No 1925/2006 of the European Parliament and of the Council, and repealing Commission Directive 87/250/EEC, Council Directive 90/496/EEC, Commission Directive 1999/10/EC, Directive 2000/13/EC of the European Parliament and of the Council, Commission Directives 2002/67/EC and 2008/5/EC and Commission Regulation (EC) No 608/2004.

 



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