The search for low glycaemic and slowly digestible starch continues, with scientists from Purdue University reporting a new starch that may lead to smaller spikes in blood sugar and perhaps ease hunger pangs.
"Starch with a slow digestion property would provide for extended glucose release along with a low glyacemic response and, thus, may have commercial application as a healthy ingredient of processed foods," wrote lead author Zihua Ao in The Journal of Agricultural and Food Chemistry.
"There are no commercial slowly digestible starch-based products available in the current food market to our knowledge."
The glycaemic index measures how quickly certain foods release carbohydrates into the body, which then raise consumers' blood glucose levels. High GI foods cause blood sugar levels to rise more rapidly.
There is growing concern about the role of inappropriate diet in chronic non-communicable conditions has prompted campaigns promoting increased consumption of fruits, vegetables and other fibre-rich foods.
At the same time, there has been considerable interest in the role of dietary carbohydrates, which has led to wider use of the glycaemic index to describe the impact that consumption of particular products will have on blood sugar and to provide consumers with information.
The scientists behind the new study used laboratory-based enzyme treatment to modify the structure of corn starch with the hypothesis that increasing the branch density of the chemical structure may decrease the rate of digestion, and reduce the release of sugar into the blood.
Using a variety of enzymes, including beta-amylase, beta-amylase plus transglucosidase, maltogenic alpha-amylase, and maltogenic alpha-amylase plus transglucosidase, the researchers tested for changes in concentrations of different types of starches.
Starches can be divided into three groups: rapidly digestible starch (RDS, digested within 20 minutes), slowly digestible starch (SDS, digested between 20 and 120 minutes), and resistant starch (RS). The latter is not digested but is fermented in the large intestine and has 'prebiotic' properties.
The Purdue researchers found that the enzyme treatment with beta-amylase, beta-amylase plus transglucosidase, maltogenic alpha-amylase, and maltogenic alpha-amylase plus transglucosidase reduced RDS by 14.5, 29.0, 19.8, and 31.0 per cent, and increased SDS by 9.0, 19.7, 5.7, and 11.0 per cent, respectively.
Using a variety of analytical techniques, Ao and co-workers report that all the enzyme treatments increased the starch branch density and the crystalline structure.
"In conclusion, partial shortening of the outer branch chains of amylopectin, and possibly amylose, by beta-amylase and maltogenic alpha-amylase reduced the overall starch digestion rate, which was related to an increase in the amount of alpha-1,6 linkages and a decrease in alpha-1,4 linkages," they concluded.
The next step will be to test these materials in human trials, said the researchers.
Foods with a low GI value keep the body's blood sugar levels relatively steady throughout the day, regulating appetite and reducing the tendency to snack. Although there is no evidence to show that a low-glycaemic index diet is any more effective than a low-fat, high GI diet for weight loss, low GI foods are increasingly being positioned as weight management foods, partly because they may also have benefits in preventing obesity-related disease like type 2 diabetes.
Source: Journal of Agricultural and Food Chemistry
Volume 55, Number 11, Pages 4540 - 4547
"Starch with a Slow Digestion Property Produced by Altering Its Chain Length, Branch Density, and Crystalline Structure"
Authors: Z. Ao, S. Simsek, G. Zhang, M. Venkatachalam, B.L. Reuhs, and B.R. Hamaker