Page 6 - Nutrinsight-3

NutrInsight • Do we need dietary polyphenols for health?
The content of polyphenols in foods
Figure 2 shows the total polyphenol content of common food sources expressed as gallic acid equivalents measured by the Folin-Ciocalteu method (gallic acid is one of the basic hydroxybenzoic acid structures, and is used as a reference for total phenolics quantification). This method evaluates the reducing ability of all phenol groups. Because of the extraction process, some reducing sugars can react as well, leading to an overestimation of total polyphenol content.
Cocoa powder and chocolate are rich in polyphenols (5953 mg/100g and 2160 mg/100g, respectively) – mainly catechins and proanthocyanidins – and dark berries such as blueberry are high too (471 mg/100g) – anthocyanins. The polyphenols content of some other foods can be lower (coffee, tea) but their high consumption may result in an important contribution to total polyphenols intake.
The content and chemical nature of these phytochemicals differ largely from one food to another and some foods contain a wide mixture of polyphenols. The Folin-Ciocalteu method does not give the nature of individual phenolic compounds in each food.
Total polyphenols content
However, there are some specific analytical methods to assess content of individual phenolic compounds.
These methods are very diverse and can vary from one lab to another leading to a disparity of results for a
same molecule analysed.
(mg/100g or 100ml) expressed as Gallic acid equivalents*
6.000 5.900
2.200 2.100
900 800 700 600 500 400 300 200 100
0
5.953
2.160
854
495
471
289
267
215
202
170
154
149
104
55
Series
Figure 2: Total polyphenols content in some foods and beverages (mg/100g or mg/100ml as Gallic Acid Equivalent measured by Folin-Cicalteu method)
Source: 1Kraft Foods internal data; 2Phenol-Explorer Database, http://www.phenol-explorer.eu/, consulted in August 2011
Importance of extraction process for accurate analysis of the polyphenols content in foods
The different analytic methods often underestimate the polyphenols content in certain foods that contains some non-extractable phenolics.
Non-extractable phenolics have been generally overlooked in food composition analysis and databases. Apples and berries contain mainly extractable polyphenols, but in other fruits, such as pears, redcurrants
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Cocoa powder 2
Dark chocolate +70% 1
Milk chocolate 2
Hazelnut 2
Blueberry 2 Strawberry 2
Soluble Coffee 2
Red wine 2
Apple 2 Whole grain bread substitute 1
Bread, Wholemeal flour 2 Whole grain biscuit 1
Black tea 2 Extra-virgin olive oil 2