Dear Susanne and Anders
In September, I prepared a presentation on organic acids and polyols that may be a useful starting point for discussing the components that might contribute to the totals used in energy calculation. It is online at:
http://www.eurofir.org/wp-content/uploads/thesauri/discussion/2013/OrgAcids&Polyols-Sep2013.pdf
This includes some suggestions on which acids might be included in Total Organic Acids (tagname OA), if this is intended to represent the total energy-contributing “organic acids”. Incidentally, as shown on slide 3, the tagname for propionic acid is PROPAC. Propanoic acid (the IUPAC name) should be added as a synonym in both the INFOODS tagname list and the EuroFIR Component Thesaurus.
F4:0 occurs in triglycerides in dairy products and seems the natural lower limit for the definition of “fatty acids”. On the other hand, the term “organic acid” includes various other carboxylic acids (and their salts? – as these presumably also contribute energy) that occur naturally, such as substituted short chain monocarboxylic acids, dicarboxylic acids, etc., as well as some food additives. However, as Anders indicates, there is no definition of “organic acid” that is well formulated; any compositional value for Total Organic Acids (tagname OA) needs to be documented in respect of the contributing acids.
With regard to Chebi, EuroFIR is not currently inputting information to the database or to its curators. Chebi provides a collection of information on the structure, nomenclature, identifiers and chemical relationships of Chemical Entities of Biological Interest. It supplements the basic information available in the EuroFIR Component Thesaurus, which as you know contains links to the corresponding Chebi entries. Chebi also connects to the citation network that is part of the Europe PubMed Central service, formerly CiteXplore. Note that the definitions for component groups in Chebi do not necessarily agree with food composition conventions. For example, the term “long-chain fatty acid” is described as “A fatty acid with a chain length ranging from C13 to C22”. However, Chebi is an important source of information on food components that it would be impractical to maintain as part of the EuroFIR Component Thesaurus or the INFOODS tagname documentation.
Hope these comments are useful,
Best wishes
Ian
Ian D Unwin Food Information Consultancy
From: Food Composition Discussion Group [mailto:[log in to unmask]] On Behalf Of Anders Møller
Sent: 24 January 2014 11:50
To: [log in to unmask]
Subject: Re: energy factor for acetic acid and other organic or fatty acids
Dear Susanne,
We may be “on dangerous grounds” here J
Please note that we are trying to be very precise in our definitions (but with some overlaps and maybe with wrong terminology) – which is fine – however, we need to keep in mind that the energy factors used in the different systems are very, very rough averages.
As Rakesh indicated, all compounds differ in their measure for heat of combustions, the longer the chain the larger the heat of combustion (energy factor).
In addition, some Chebi definitions may come from us (EuroFIR) – Ian Unwin will know that.
I think that you should stick to the IUPAC definitions for fatty acids (http://goldbook.iupac.org/F02330.html), which says
“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.”
The definition’s extension include some of the “organic acids”, the very short chain carboxylic acids (F2:0 and F3:0), but there are quite a lot of other “organic acids” (carboxylic acids), which are not necessarily “usually unbranched and even-numbered”.
Please also note that the term “organic acid” is not defined in the IUPAC system – the correct term is carboxylic acid - I may get into trouble here J
In the explanation of the Atwater system by Merrill and Watt, a few “organic acids” are listed (USDA AH 74, one of the USDA classics, http://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/Classics/ah74.pdf):

and we could add other “organic acids” like propionic/propanoic acid, sorbic acid, etc., commonly appearing in foods both naturally and as food additives.
And yes, you see vitamin C (ascorbic acid) among the “organic acids”, and if you want to be very precise, you should count the energy from the ascorbic acid too.
But “being precise” and “energy calculation” is a contradiction J
Be pragmatic:
fatty acids are carboxylic acids with “a chain of 4 to 28 carbons” - fat energy factor 37kJ/g (9 kcal/g) in EU regulation – the rest – among these F2:0 and F3:0 (although pion means fat in Greek (from Wikipedia)) - are currently “organic acids” with energy factor 13 kJ/g (3 kcal/g) in EU regulation.
All the best,
Anders
Anders Møller
Danish Food Informatics
Borgediget 12
DK-4000 Roskilde, Denmark
Websites: Danish Food Informatics (http://www.danfood.info)
SciName Finder™ (http://www.sciname.info)
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From: Food Composition Discussion Group [mailto:[log in to unmask]] On Behalf Of Susanne Westenbrink
Sent: 24 January 2014 10:48
To: [log in to unmask]
Subject: energy factor for acetic acid and other organic or fatty acids
Dear all,
Many thanks to Esther, Erling, Anders, Rakesh and Paul for replying to our question. This has helped to get things clearer.
We do use the European legislation to calculate energy in foods, which means that we apply specific factors for e.g. organic acids and polyols. My main question was about where to put acetic acid, as this compount is both indicated as organic acid and fatty acid F2;0. So far we only have zero values in our database, so any change will not have an inpact on energy values. When adding an acetic acid value for vinegar and related foods we need to apply the correct approach.
From the discussion we have concluded that acetic acid (F2:0) must be treated as an organic acid and not as fatty acid. Acetic acid it is a building block of natural fatty acids but, unlike them, does not occur in natural triglycerides (Chebi). And with the usual analytical methods, they do not turn up in the value for fat/fatty acids. You need special analytical methods to determine the amount of organic acids, as indicated by Anders. In the NEVO database we will attribute ~3 kcal /g organic acids, and not include acetic acid in the sum of saturated fatty acids.
To continue the discussion:
Following this, the next question pops up for other short chain fatty acids/organic acids. On internet (http://www.cyberlipid.org/fa/acid0001.htm#1) I found information that stated that short chain fatty acids (below 4- 6 Carbons) should/could be regarded as organic acids. Up to 6 (or 4) carbon atoms, organic acids are considered "short-chain organic acids", they have substantial solubility in water. Furthermore, they do not behave physiologically like other fatty acids since they are more rapidly digested and absorbed in the intestinal tract and have unique properties in regulating sodium and water absorption through the mucosal epithelium. Biochemically, they are more closely related to carbohydrates than to fats. However I am not sure how reliable this website is.
Propanoic acid is listed as organic acid in the EuroFIR component thesaurus and as fatty acid by Chebi (I could not find it in the INFOODS tagnames). Is this measured through fatty acid analyses methods? Is it a relevant component in food? If available in a food comp database, should 3 or 9 kcal be calculated for energy?
What is your opinion on this?
Butyric acid (F4:0) is classified as fatty acid in both the EuroFIR component thesaurus and the Chebi database. I know this is measured in fatty acid analyses, we have several values. My conclusion would be that F4:0 must be treated as a fatty acid, yielding ~ 9 kcal/g. (This what we have been doing all the time).
Do you agree on this conclusion for butyric acid?
EuroFIR component thesaurus:
Acetic acid classified as organic acid, with synonym F2;0
Propanoic acid: classified as organic acid with synonym F3;0
Butyric acid classified as saturated fatty acids (F4:0)
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Susanne Westenbrink
Rijksinstituut voor Volksgezondheid en Milieu (RIVM) / National Institute for Public Health and the Environment
Centrum voor Voeding, Preventie en Zorg / Centre for Nutrition, Prevention and Health Services
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The Netherlands
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