Abstract
Background
Proanthocyanidins (PAC) are oligomers and polymers of flavan-3-ols with putative health benefits. PAC are prevalent in a wide variety of natural products and dietary supplements.
Objective
An inter-laboratory study was conducted to validate the 4-(dimethylamino)cinnamaldehyde (DMAC) colorimetric assay using a 96-well plate spectrophotometer for the accurate quantification of PAC in cranberry products and to evaluate the comparison of the procyanidin A2 (ProA2) dimer and cranberry PAC (c-PAC) reference standards.
Methods
Four test materials analyzed in this study included cranberry fiber powder, cranberry extract powder, concentrated cranberry juice, and a solution of cranberry PAC (30%, w/v). The samples were homogenized, extracted, sonicated, centrifuged, and analyzed using a 96-well plate spectrophotometer.
Results
Linearity for both the ProA2 and c-PAC standards was determined from 4.053 to 50.666 µg/mL and from 13.520 to 135.95 µg/mL, respectively. The relative standard deviation of repeatability (RSDr) values for the four materials analyzed, using both ProA2 and c-PAC standards, met the Standard Method Performance Requirements (SMPR®). Inter-laboratory precision using Horwitz ratio (HorRat) values for the four materials analyzed, using both ProA2 and c-PAC standards, satisfies the acceptance range in Appendix K of the Official Methods of Analysis (2003): Guidelines for Dietary Supplements and Botanicals. The limit of quantification (LOQ) was estimated to be 3.16 µg/mL.
Conclusions
The results produced from this study demonstrate the utility of the c-PAC standard over the ProA2 standard and the advantages of using a 96-well plate spectrophotometer for the accurate quantification of PAC.
Highlights
The use of a 96-well plate reader and c-PAC reference standard in the DMAC method improves accuracy and percision for quantification of soluble proanthocyanidins in cranberry foods and dietary supplements.
Identification and Quantification Methodology for the Analysis of Suspected Illegal Dietary Supplements: Reference Standard or no Reference Standard, that the Question
