Writing in the Journal of Agricultural and Food Chemistry , the researchers describe the production of a food-grade mulberry powder with an optimized content of 1-deoxynojirimycin (DNJ) content, a compound shown to inhibit the action of the glucosidase enzyme that controls the digestion of carbohydrates.
"This study suggests that the newly developed DNJ-enriched powder can be used as a dietary supplement for preventing diabetes mellitus," wrote lead author Toshiyuki Kimura from Tohoku University, in collaboration with researchers from National Agricultural Research Center for Tohoku Region, Minato Pharmaceutical Company, and Nippon Medical School.
An estimated 19 million people are affected by diabetes in the EU 25, equal to four per cent of the total population.
This figure is projected to increase to 26 million by 2030.
In the US, there are over 20 million people with diabetes, equal to seven per cent of the population.
The total costs are thought to be as much as $132bn, with $92bn being direct costs from medication, according to 2002 American Diabetes Association figures.
While DNJ has been shown to inhibit glucosidase, the concentration of the compound in commercial mulberry products is extremely low, state the researchers, with levels as low as about 0.1 per cent.
Kimura and co-workers set about producing a food-grade mulberry powder with high DNJ content, and then determining the optimal dose of the DNJ-enriched powder needed to suppress blood glucose levels after a meal through clinical trials.
Using hydrophilic interaction chromatography with evaporative light scattering detection the researchers obtained a mulberry powder containing 1.5 per cent DNJ.
"Young mulberry leaves taken from the top part of the branches in summer contained the highest amount of DNJ," wrote the authors.
To test the efficacy of the extract, the researchers recruited health volunteers and assigned them to receive 0, 0.4, 0.8, and 1.2 g of DNJ-enriched powder, giving a corresponding dose of DNJ of 0, 6, 12, and 18 mg.
This was followed by 50 g of sucrose.
Blood glucose and insulin levels were measured before sucrose consumption, and again 30-180 minutes later.
"A human study indicated that the single oral administration of 0.8 and 1.2 g of DNJ-enriched powder significantly suppressed the elevation of postprandial blood glucose and secretion of insulin, revealing the physiological impact of mulberry DNJ (effective dose and efficacy in humans)," concluded the researchers.
Further research is needed to examine the efficacy of the extract in other population groups, including overweight and obese subjects who are more susceptible to type-2 diabetes.
The research adds to a growing body of evidence of the potential health benefits of berries that has filtered through to the consumers and has seen demand increase.
Indeed, sales of blueberries, for example, are reported to have rocketed by 130 per cent, raspberry sales are said to have grown by 62 per cent in the last two years, a strawberry sales in the UK are reported to have increased by 34 per cent during the last two years.
Source: Journal of Agricultural and Food Chemistry Published in ASAP Article 10.1021/jf062680g S0021-8561(06)02680-X "Food-Grade Mulberry Powder Enriched with 1-Deoxynojirimycin Suppresses the Elevation of Postprandial Blood Glucose in Humans" Authors: T. Kimura, K. Nakagawa, H. Kubota, Y. Kojima, Y. Goto, K. Yamagishi, S. Oita, S. Oikawa, and T. Miyazawa