Bioactive constituents in aronia berries

摘要

The aim of this thesis was to investigate some of the potential health benefits of aronia berries with main focus on the phenolic substances. Extractions and fractionations of aronia berries were performed to obtain several crude extracts and subfractions. In addition, well known constituents of aronia berries (anthocyanins, procyanidins and phenolic acids) were isolated. The different samples obtained were then tested in various in vitro bioassays to determine their biological activities as antioxidants, a-glucosidase inhibitors, CYP3A4 inhibitors, and antibacterial agents.Pure anthocyanins and anthocyanin-rich extracts were found to be potent a-glucosidase inhibitors compared to the positive control acarbose, the active principle in an anti-diabetic drug. a-Glucosidase plays a vital role in digestion of carbohydrates and by inhibition of this enzyme, it might be possible to control postprandial hyperglycemia which is important for diabetic patients. Antioxidant activity was assessed by DPPH radical scavenging and by inhibition of 15-lipoxygenase and xanthine oxidase. In general, the substances tested displayed strong radical scavenging and 15-LO inhibitory effects, but exhibited less activity towards XO.CYP3A4 is an important-drug metabolizing enzyme, and any change of its activity may lead to pharmacokinetic interactions. Aronia substances were investigated for their CYP3A4 inhibitory effects, and it was shown that procyanidin B5 and subfraction Seph g, rich in proanthocyanidins with a high degree of polymerization, were potent inhibitors of this protein. In addition, the inhibitory activity of proanthocyanidin-containing subfractions was correlated to the degree of polymerization of these substances.The formation of bacterial biofilms is a well known health problem, as bacteria within such a structure are more difficult to eradicate. Aronia substances were added to planktonic cultures of Escherichia coli and Bacillus cereus in order to measure their influence on biofilm formation. Results showed that the majority of the samples possessed a biofilm inhibitory activity against the Gram-positive B. cereus, but fewer samples were active against the Gram-negative E.coli.Minor differences in chemical structure, for example between procyanidin B2 and B5, gave rise to considerable differences in biological activities such as CYP3A4 inhibition and inhibition of biofilm formation. Also, biological activity seemed to be influenced by the sugar unit linked to the anthocyanidin.Four different cultivars of aronia were studied with respect to their phenolic composition and their biological activities. Aronia prunifolia contained the highest amount of total phenolics, anthocyanins, and proanthocyanidins. Despite the differences in chemical composition between the cultivars, which could be explained at least partly by unequal growing conditions, only minor differences in biological activity were found.