Multi-laboratory validation of a standard method for quantifying proanthocyanidins in cranberry powders

USDA-ARS, Arkansas Children's Nutrition Center, Little Rock, AR 72202, USA.
Journal of the Science of Food and Agriculture (Impact Factor: 1.71). 07/2010; 90(9):1473-8. DOI: 10.1002/jsfa.3966
Source: PubMed


The objective of this study was to validate an improved 4-dimethylaminocinnamaldehyde (DMAC) colorimetric method using a commercially available standard (procyanidin A2), for the standard method for quantification of proanthocyanidins (PACs) in cranberry powders, in order to establish dosage guidelines for the uropathogenic bacterial anti-adhesion effect of cranberry.
Commercially available cranberry samples were obtained (five from U.S. sources and six from European sources) for PAC quantification in five different analytical laboratories. Each laboratory extracted and analyzed the samples using the improved DMAC method. Within-laboratory variation (mean +/- SD) was 4.1 +/- 1.7% RSD (range, 2.3-6.1% RSD) and the between laboratory variability was 16.9 +/- 8.5% RSD (range, 8-32% RSD). For comparative purposes, the cranberry samples were alternatively quantified using weights of extracted PACs (gravimetric). The correlation coefficient between the two methods was 0.989.
This improved DMAC method provides a simple, robust and relatively specific spectrophotometric assay for total PACs in cranberry samples using commercially available procyanidin A2 dimer as a standard. DMAC is most useful within a given type of food such as cranberries, but may not be appropriate for comparing concentrations across different food types, particularly in those cases where large differences exist among the relative amounts of each oligomer and polymer.

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    • "Declared total PACs in CFP determined by the 4-dimethylaminocinnamaldehyde (DMAC) method (Prior et al., 2010) was 0.56%, and this powder was applied for the clinical trial. The results of our secondary metabolite determination of CFP by HPLC-ESI-MS/ MS are shown in Table 1; PACs have been analysed according to Jungfer et al., 2012 (Table 2). "
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    • "Total phenol content of the extract was reported as gallic acid equivalents (GAE). Proanthocyanidins were quantified by reaction with 4-(dimethylamino)-cinnamaldehyde (DMAC) as previously described and reported as catechin equivalents (CE) (Kim, Park, Wegner, Bolling, & Lee, 2013; Prior et al., 2010). "
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    • "This method reads at 640 nm and is therefore less sensitive to interference from anthocyanins. Furthermore, DMAC reagent reacts only with compounds containing metasubstituted dihydroxybenzene rings, a single bond at the 2,3-posi- tion of the C-ring and no carbonyl at C4 making it particularly sensitive to flavanols (Prior et al., 2010). Total PAC in RD lines ranged between 1.63 and 2.89 mg PAC/g and in the ND lines between 0.02 and 0.05 mg PAC/g (Fig. 1B). "
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