Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/15/2007
Publication Date: 12/15/2007
Citation: Prior, R.L. 2007. Proanthocyanidins: Challenges in understanding the chemistry, metabolism and health benefits [abstract]. In: Proceedings of SICC-5: Singapore International Chemistry Conference 5 & APCE Asia-Pacific International Symposium on Microscale Separation and Analysis, December 16-19, 2007, Singapore, China. p. 6:159.
Interpretive Summary: Proanthocyanidins are large complex compounds found in many foods. These substances have been shown to have potential health benefits. However, little is known about their dietary intake because quantitative information on the proanthocyanidin profiles in foods is lacking. Methods have been developed and applied to the analysis of proanthocyanidins in different foods. Concentrations of proanthocyanidins in common and infant foods sampled from the U.S. are now available through the USDA Nutrient Database. Proanthocyanidins account for a major fraction of the total flavonoids ingested in the Western diet. Procyanidins may have health benefits; however, the bioavailability of procyanidins is not well understood. In rats, total proanthocyanidins and polymers disappeared progressively from the gastrointestinal tract, and significant degradation occurred in the cecum and colon. Catechins from sorghum procyanidins were bioavailable; however, bacteria-derived phenolic acids were the predominant metabolites of procyanidins.
Technical Abstract: Oligomeric and polymeric flavan-3-ols are better known as proanthocyanidins or condensed tannins. They are ubiquitous and present as the second most abundant natural phenolics after lignin. The flavan-3-ol units are linked mainly through a C4'C8 bond, but the C4'C6 bond also exists (both called B-type). The flavan-3-ol units can also be doubly linked by an additional ether bond between C2'O7 (A-type). The size of proanthocyanidin molecules can be described by degree of polymerization (DP) Chemistry: A normal phase HPLC-MS method with fluorescence detection was used to establish a database of proanthocyanidins in foods. The gradient of the ternary mobile phase was used that provided separation of proanthocyanidin monomers through decamers and eluted all the polymers beyond those as a distinct peak. Proanthocyanidin polymers were present as the dominant proanthocyanidin in cacao, blueberry, sorghum, and cranberry; epicatechin was present as the extension unit in these foods; however, the composition of terminal units varied considerably between catechin and epicatechin or an A-type dimer linkage in the case of cranberry. Recently, a novel HPLC method for the quantitative determination of flavanols and procyanidins has been developed. Chromatographic separation is based on degree of polymerization (DP) using a diol stationary phase column with a binary gradient of acetonitrile and methanol-water. Quantitation is achieved with fluoresence detection (EX 230 nm/EM 321 nm) using external standards giving linear responses over a wide range of concentrations with increased sensitivity compared to the normal phase method. Metabolism: Procyanidins may have health benefits; however, the bioavailability of procyanidins is not well understood. In rats, total procyanidins and polymers disappeared progressively from the gastrointestinal tract, and significant degradation occurred in the cecum and colon. Catechins from sorghum procyanidins were bioavailable; however, bacteria-derived phenolic acids were the predominant metabolites of procyanidins. Procyanidins were degraded in the gastrointestinal tract, but depolymerization was not observed. Health Effects: Little is known about the dietary intake of proanthcyanidins because quantitative information on the profiles in foods has not been available. Proanthocyanidins in common and infant foods sampled from the U.S. were analyzed and concentrations are now available through the USDA Nutrient Database. The average daily intake of proanthocyanidins in the U.S. population has been estimated to be 57.7 mg/person/day based on our food concentration data and food intake data (USDA - CSFII, 1994–1996). Monomers, dimers, trimers, and those above trimers contribute to 7.1%, 11.2%, 7.8%, and 73.9% of total proanthocyanidins, respectively. The major sources of proanthocyanidins in the American diet are apples (32.0%), followed by chocolate (17.9%) and grapes (17.8%). Proanthocyanidins account for a major fraction of the total flavonoids ingested in the Western diet. Proanthocyanidins should be considered when studying the epidemiological association between flavonoid intake and chronic diseases.