Assessment of experimental factors affecting the sensitivity and selectivity of the spectrophotometric estimation of proanthocyanidins in foods and nutraceuticals

The assessment of a reliable method for the determination of active proanthocyanidins (PACs) in functional foods, nutraceuticals, and foodstuffs is still a pending analytical challenge. In general, pharmaceutical and food companies accept the assay based on 4-dimethylaminocinnamaldehyde (DMAC) as an overall index of PACs, although these values provided confuse information of the actual bioactivity of the product. Besides, obtaining accurate and precise results is difficult because of the complexity of the sample matrices and the differential selectivity of analytes. Here, we have investigated in detail those experimental factors contributing to the PAC-DMAC derivatives, and we have explored the possibilities for increasing the selectivity of the reaction to detect the fraction of PAC molecules with antibacterial properties. In this regard, the use of harsh conditions, especially working at high temperature, contributes to the formation of the desired derivatives and the degradation of the undesired ones. Unfortunately, the selective detection of A-type species based on DMAC derivatization was not realistic. Another goal of the study was the development of a spectrophotometric assay for the determination of the total content of flavanols. In this case, experimental conditions were chosen to reach high responses for all the compounds. Working under mild conditions of temperature and reaction time (20 °C and 20 min), the method was suitable to estimate the overall flavanol content of food supplements, nutraceuticals, and commercial fruit juices.