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NutrInsight • Do we need dietary polyphenols for health?
and kiwi fruits, up to half their polyphenols are non-extractable by standard methods. Bananas are an extreme example and virtually all their polyphenols are non-extractable [Tarascou et al., 2010]. This means that the values in databases are underestimated and therefore polyphenol consumption is probably higher than estimates.
FOOD
% EXTRACTABLE
% NON-EXTRACTABLE
Apple and berries
90-100
0-10
Grape
50
50
Pear
50
50
Cranberry
50
50
Red currant
50
50
Kiwi fruit
20
80
Banana
0
100
Table 1: Distribution of polyphenols between extractable and non-extractable compounds in some fruits
Source : Adapted from Tarascou et al., 2010
Polyphenols food composition database
The measures of polyphenols content in foods have allowed building food composition databases on polyphenol content, either global or focussed on specific subclasses.
A USDA database has been available since 2004 [www.ars.usda.gov] to estimate proanthocyanidin contents of foods; databases for isoflavones and flavonoids have been available since 2008 and 2011. These have all been based on a compilation of literature sources.
A very exciting recent development is the Phenol-Explorer web based database [www.phenol-explorer.eu] which has been collated from published papers by Dr Augustin Scalbert and colleagues from the Institut National de la Recherche Agronomique in France (INRA). This database covers 502 polyphenols in 452 foods. It includes not only flavonoids, but also phenolic acids, lignans, and stilbenes, with invidual glycosides and esters. The database provides information about the type of polyphenols, their food source content, their metabolites, and their pharmacokinetics.
The EuroFIR BASIS is also an on-line database developed within the EuroFIR NoE (European Food Information Ressource Network of Excellence). It gathers composition and biological activity data for plants and plant foods, compiled from critically evaluated published data [http://ebasis.eurofir.org/Default.asp].
However, the problems of non-extractable polyphenols and non-homogeneity of analysis methods still exists; even the most comprehensive database will only be as good as the analytical data that has been published in the literature. Good quality polyphenol databases are key for accurate estimations of polyphenol intake of foods in populations. We urgently need standardisation of the analysis methods, especially for non-extractable polyphenols, to better characterise the polyphenol profile in foods in our diet.
1.2 Consumption of dietary polyphenols
Estimation of daily diet intake of total polyphenols
The mean daily total polyphenol intake could reach more than one gram [Pérez-Jiménez et al., 2011]. This French study has given us recent information on total polyphenol intake based on the SUVIMAX French cohort (1995-1996). The SUVIMAX cohort consisted of 4942 middle-aged participants who consumed a total of 337 polyphenols with at least half of the population consuming 258 polyphenols [Pérez-Jiménez et al., 2011].
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