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Cranberry compounds show potential for blood sugar management strategies

1 commentBy Stephen DANIELLS , 11-Feb-2013
Last updated the 11-Feb-2013 at 15:15 GMT

Cranberry compounds show potential for blood sugar management strategies

Tannin compounds from cranberries and pomegranate may slow the digestion of starch and offer specific dietary approaches to control blood sugar levels, suggests a new study.

Extracts from cranberry in particular were associated with significant inhibition of the starch digesting enzymes alpha-amylase and glucoamylase, with pomegranate and grape tannins also showing good inhibitory effects, Journal of Agricultural and Food Chemistry .

 “Possible practical applications of these results stem from the finding that condensed tannins from selected plants inhibit alpha-amylase and glucoamylase activity in vitro, albeit to different degrees, thus slowing digestion of starch,” wrote researchers from the US Army Natick Soldier Research, Development & Engineering Center (NSRDEC), James Madison University, Rutgers University, and Ohio State University.

“This inhibitory effectiveness suggests the likelihood of specific dietary approaches for modulating digestion rates in vivo and thus assisting in control of blood glucose levels.”

Glycemic control

One approach to controlling blood sugar is to inhibit the action of specific enzymes such as alpha-amylase and alpha-glucosidase, which are responsible for carbohydrate digestion.

However, current glucosidase inhibitors, such as acarbose and miglitol, are said to produce diarrhea and other intestinal disturbances.

“Slowed starch digestion can theoretically increase satiety by modulating glucose ‘spiking’ and depletion that occurs after carbohydrate-rich meals,” explained the researchers, led by NSRDEC’s Ann Barrett.

Study details

Barrett and her co-workers tested tannins from pomegranate, cranberry, grape, and cocoa on their ability to bind to the digestive enzymes alpha-amylase and glucoamylase.

The lab tests showed that the tannins inhibited the enzymes by different amounts. For alpha-amylase, the order of inhibiting activity was cranberry > grape > pomegranate > cocoa.

Regarding glucoamylase, cranberry, cocoa and grape tannins were all able to inhibit its activity to varying degrees.

“In general, larger and more complex tannins, such as those in pomegranate and cranberry, more effectively inhibited the enzymes than did less polymerized cocoa tannins,” explained Barrett and her co-workers.

Source: Journal of Agricultural and Food Chemistry
Published online ahead of print, doi: 10.1021/jf304876g
“Inhibition of alpha-Amylase and Glucoamylase by Tannins Extracted from Cocoa, Pomegranates, Cranberries, and Grapes”
Authors: A. Barrett, T. Ndou , C.A. Hughey , C.Straut , A. Howell , Z. Dai, G. Kaletunc

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Antioxidant activity and phenols of pomegranate peels juices and seeds

Another study was undertaken in our lab in Greece in order to determine the antioxidant activity and the total phenols, total flavonoids, hydrolysable tannins and ellagic acid contents in the juices, peel and seed extracts of two pomegranate cultivars from mainland Greece. In total the peels from both pomegranate cultivars had higher antioxidant activity and phenol contents compared to juices and seeds.

In addition, the cultivar from Central Macedonia in its peel homogenates had higher total phenol, total flavonoid, hydrolysable tannins and ellagic acid contents than the cultivar from Thrace. From the results it can be concluded also that different solvents (methanol, water) at temperatures 24 and 40 C used during the extraction process of the peels may affect their antioxidant properties and phenol contents.

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Posted by Dr. Vasiliki Lagouri
18 February 2013 | 10h32

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