Characterization of Phytochemicals Involved in the Darkening of Cranberry Beans (Phaseolus vulgaris L.) and Their Potential Health Benefits




Chen, Peter Xin

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University of Guelph


Post-harvest darkening (PHD) occurring during storage of dry beans (Phaseolus vulgaris L.) has a negative impact on consumer preference. Prevention of PHD has aesthetic appeal however, it may come at the expense of health-benefiting phytochemicals. In this study, regular- (RD) and non-darkening (ND) cranberry beans were compared for their phytochemical contents and measures of antioxidant and anti-inflammation activities. Seed coats and whole beans of RD and ND cultivars were examined using HPLC DAD/LC-ESI-MSn and NMR along with in vitro chemical methods (total phenolic; TPC, total flavonoid; TFC, total proanthocyanidin; PAC). Free, conjugated and bound phenolics were sequentially extracted and examined separately. PHD under greenhouse conditions for 21 d decreased TPC, TFC and PAC contents in RD beans (p < 0.05). An unknown compound saw significant increase in concentration following PHD. Purified extracts of RD and ND beans displayed strong cellular antioxidant activity in RD and dose-dependent attenuation of TNF-α-induced pro-inflammatory cytokine IL-8 secretion in a Caco-2 cell model (p < 0.05). The extracts displayed prevention of inhibition of endogenous antioxidant enzymes such as SOD, CAT, GPx and GR as well as GSH under stress conditions. Monomeric and oligomeric flavonoids were only found in RD beans. TPC and overall antioxidant activities (FRAP, DPPH, and ORAC) were significantly higher (p < 0.05) in RD seeds compared to ND. Lipophilic extracts of whole RD and ND beans were rich in polyunsaturated fatty acids (69.20–76.89%). Simulated gastrointestinal digestion was performed on cooked beans to assess phenolic bioaccessibility. Phenolics in the non-digestible fractions of RD and ND were released upon hydrolysis with carbohydrase enzymes. Results from this study suggest that flavonoids may play a key role in the PHD trait. However, despite the higher concentration of flavonoids present in RD beans, under physiological conditions, health benefits derived from RD and ND beans became less apparent.



dry beans, phytochemicals, polyphenols, phenolics, antioxidant, antiinflammation, caco-2 cells, inflammation, post harvest darkening, cranberry beans, health, flavonoids, catechin