Critical reevaluation of the 4-(dimethylamino)cinnamaldehyde assay: Cranberry proanthocyanidin standard is superior to procyanidin A2 dimer for accurate quantification of proanthocyanidins in cranberry products

The 4-(dimethylamino)cinnamaldehyde (DMAC) assay is currently used to quantify proanthocyanidin (PAC) content in cranberry products. In a multi-operator/multi-day study design, a cranberry proanthocyanidin (c-PAC) standard was compared to procyanidin A2 (ProA2) dimer for accurate quantification of PAC in commercial cranberry juices, lab generated cranberry blends and cranberry powders. The c-PAC standard reflects the structural heterogeneity of cranberry PAC degree of polymerization, hydroxylation pattern and ratios of 'A-type' to 'B-type' interflavanyl bonds. Use of the c-PAC standard to quantify PAC content in cranberry samples resulted in values that were 3.6 times higher than those determined by ProA2. Overall, there was no effect (P > 0.05) of operator or day on estimation of PAC concentration. The adoption of c-PAC standard should be considered as an improvement over the use of ProA2 for accurate quantification of cranberry PAC. Improved standardization of bioactive PAC components in functional cranberry foods will aid in establishment of dosage guidelines.