title: Different polyphenolic components of soft fruits inhibit alpha-amylase and alpha-glucosidase.
abstract: Polyphenol-rich extracts from soft fruits were tested for their ability to inhibit alpha-amylase and alpha-glucosidase. All extracts tested caused some inhibition of alpha-amylase, but there was a 10-fold difference between the least and most effective extracts. Strawberry and raspberry extracts were more effective alpha-amylase inhibitors than blueberry, blackcurrant, or red cabbage. Conversely, alpha-glucosidase was more readily inhibited by blueberry and blackcurrant extracts. The extent of inhibition of alpha-glucosidase was related to their anthocyanin content. For example, blueberry and blackcurrant extracts, which have the highest anthocyanin content, were the most effective inhibitors of alpha-glucosidase. The extracts most effective in inhibiting alpha-amylase (strawberry and raspberry) contain appreciable amounts of soluble tannins. Other tannin-rich extracts (red grape, red wine, and green tea) were also effective inhibitors of alpha-amylase. Indeed, removing tannins from strawberry extracts with gelatin also removed inhibition. Fractionation of raspberry extracts on Sephadex LH-20 produced an unbound fraction enriched in anthocyanins and a bound fraction enriched in tannin-like polyphenols. The unbound anthocyanin-enriched fraction was more effective against alpha-glucosidase than the original extract, whereas the alpha-amylase inhibitors were concentrated in the bound fraction. The LH-20 bound sample was separated by preparative HPLC, and fractions were assayed for inhibition of alpha-amylase. The inhibitory components were identified as ellagitannins using LC-MS-MS. This study suggests that different polyphenolic components of fruits may influence different steps in starch digestion in a synergistic manner.
authors.affiliation: Quality, Health and Nutrition Programme, Genes to Products Theme, Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA, UK. gmcdou@scri.sari.ac.uk
authors.forename: Gordon J
authors.initials: GJ
authors.lastname: McDougall
authors.forename: Faina
authors.initials: F
authors.lastname: Shpiro
authors.forename: Patricia
authors.initials: P
authors.lastname: Dobson
authors.forename: Pauline
authors.initials: P
authors.lastname: Smith
authors.forename: Alison
authors.initials: A
authors.lastname: Blake
authors.forename: Derek
authors.initials: D
authors.lastname: Stewart
mesh_terms: D000872:Anthocyanins / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005419:Flavonoids / Q000032:analysis* / Q000494:pharmacology*; D031985:Fragaria / Q000737:chemistry; D005638:Fruit / Q000737:chemistry*; D065089:Glycoside Hydrolase Inhibitors; D013058:Mass Spectrometry; D010636:Phenols / Q000032:analysis* / Q000494:pharmacology*; D010936:Plant Extracts / Q000494:pharmacology; D059808:Polyphenols; D027824:Rosaceae / Q000737:chemistry; D013634:Tannins / Q000032:analysis; D000516:alpha-Amylases / Q000037:antagonists & inhibitors*
chemical_list: D000872:Anthocyanins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D065089:Glycoside Hydrolase Inhibitors; D010636:Phenols; D010936:Plant Extracts; D059808:Polyphenols; D013634:Tannins; D000516:alpha-Amylases