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Composition of tomatoes and tomato products in antioxidants (WG1) page 93
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area related.
The concentration of the ascorbic acid is calculated with external standard and peak
9.3 polyphenols
All information about polyphenol analysis was taken from the very good review of K.
Robards and M. Antolovich, Analyst, vol 122, 11-34, 1997.
Many procedures have been developed for flavonoid compounds. The design of the
analytical procedure will depend very much on the analysis.
9.3.1 Colorimetric method
Total phenolics were most conviently assessed by spectrophotometric measurement on
a simple extract of plant. Many difficulties are associated with this system. First exhaustive
extraction with alcoholic and aqueous alcoholic solvents is likely to leave behind much tannin
and other bound at the cell wall. Second, the diversity of phenolics means that the selection of
a reagent and absorbing wavelength will be a compromise. Colorimetric methods rely on the
reaction of the flavonoid with one of a number of reagent of varying selectivity. Folin-
Ciocalteu and vanillin are the classic reagents however Folin reagent react with coumpounds
other than the target phenols and interfering reductants must be removed prior the assay.
9.3.2 HPLC Determination
Sample preparation
Flavonoids are generally stable compounds and may be extracted from the dried,
ground plant material with cold or hot solvents. Suitable solvents for this purpose are aqueous
mixtures with ethanol, methanol, acetone and dimethylformamide. This procedure is
unsuitable for anthocyanins and the less polar aglycones such as flavanones, isoflavones and
flavonols. The latter are more soluble in chloroform, ethoxyethane and ethyl-acetatemethanol.
The need of a clean-up step depends on the sample type and method of extraction.
Carotenoid and chlorophyll pigments can be removed by liquid-liquid extraction with hexane