Different polyphenolic components of soft fruits inhibit alpha-amylase and alpha-glucosidase

J Agric Food Chem. 2005 Apr 6;53(7):2760-6. doi: 10.1021/jf0489926.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anthocyanins / analysis
  • Chromatography, High Pressure Liquid
  • Enzyme Inhibitors / pharmacology*
  • Flavonoids / analysis*
  • Flavonoids / pharmacology*
  • Fragaria / chemistry
  • Fruit / chemistry*
  • Glycoside Hydrolase Inhibitors*
  • Mass Spectrometry
  • Phenols / analysis*
  • Phenols / pharmacology*
  • Plant Extracts / pharmacology
  • Polyphenols
  • Rosaceae / chemistry
  • Tannins / analysis
  • alpha-Amylases / antagonists & inhibitors*


  • Anthocyanins
  • Enzyme Inhibitors
  • Flavonoids
  • Glycoside Hydrolase Inhibitors
  • Phenols
  • Plant Extracts
  • Polyphenols
  • Tannins
  • alpha-Amylases