Different Polyphenolic Components of Soft Fruits Inhibit α-Amylase and α-Glucosidase

G.J. McDougall, F Shpiro, P. Dobson, P. Smith, A. Blake, D. Stewart

    Research output: Contribution to journalArticle

    Abstract

    Polyphenol-rich extracts from soft fruits were tested for their ability to inhibit a-amylase and a-glucosidase. All extracts tested caused some inhibition of a-amylase, but there was a 10-fold difference between the least and most effective extracts. Strawberry and raspberry extracts were more effective a-amylase inhibitors than blueberry, blackcurrant, or red cabbage. Conversely, a-glucosidase was more readily inhibited by blueberry and blackcurrant extracts. The extent of inhibition of a-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 a-glucosidase. The extracts most effective in inhibiting a-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 a-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 a-glucosidase than the original extract, whereas the a-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 a-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.
    Copyright © 2005 American Chemical Society
    Original languageEnglish
    Pages (from-to)2760-2766
    Number of pages7
    JournalJournal of Agricultural and Food Chemistry
    Volume53
    Issue number7
    DOIs
    Publication statusPublished - 2005

    Keywords

    • α-Amylase
    • α-glucosidase
    • anthocyanins
    • ellagitannins
    • inhibition
    • starch digestion

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