Location: Arkansas Children's Nutrition CenterTitle: Multi-laboratory validation of a standard method for quantifying proanthocyanidins in cranberry powders Author
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2010
Publication Date: 7/22/2010
Citation: Prior, R.L., Fan, E., Ji, H., Howell, A., Nio, C., Payne, M.J., Reed, J. 2010. Multi-laboratory validation of a standard method for quantifying proanthocyanidins in cranberry powders. Journal of Agricultural and Food Chemistry. 90(9):1473-1478. Interpretive Summary: Cranberry has been utilized traditionally for prevention of urinary tract infections, and clinical research supports this claim. An important mechanism of action may be the bacterial anti-adhesion activity attributed to ingesting cranberry products. However, there has not been any readily available standardized analytical method to quantitate the active components (proanthocyanins) in cranberry that prevent urinary tract infections. The purpose of this study was to validate an improved colorimetric method for quantitation of cranberry proanthocyanidins. Results from the study have demonstrated that this method can be utilized worldwide as an accurate, reproducible, inexpensive, and rapid standard method for quantitation of proanthocyanidins in cranberry juice and powders. The procedure uses a commercially available reference standard. Use of this method will be critical as the cranberry industry attempts to move forward with a "health claim" for cranberry products in preventing urinary tract infections.
Technical Abstract: 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.