Substrate processing alters starch digestibility.

Physiologically, resistant starch is a dietary starch that resists digestion in the small intestine, and which is available for bacterial fermentation in the large intestine. Resistant starch, in addition to traditional dietary fibers, may contribute significantly to the health benefits of those who are on plant-based diets.

In addition to resistant starch, two other classes of dietary starch exist: rapidly and slowly digested starch. Starch fractions can vary widely both in their concentration and composition in food ingredients. These starch fractions vary in the rate or the extent of digestibility and may alter the digestibility of other nutrients. In addition, chemically modified starches are unique types of resistant starch that are gaining interest as food ingredients due to their tailorability for specific food applications.

Researchers at the University of Illinois have determined concentrations of rapidly and slowly digested starch and resistant starch in numerous foods and food ingredients. While starch concentration and starch fraction distribution can vary due to the type of substrate, the results imply that substrate processing alters starch digestibility, increasing the concentrations of rapidly digested starch and decreasing the concentrations of resistant starch.

Investigators also compared the in vitro hydrolytic starch digestibility of chemically modified and unmodified starch sources. While the extent of starch digestibility decreased, the relative rate of starch digestion was not significantly affected. Although it is widely recognized that dietary starches are not completely digested in the small intestine, little information is available on the concentrations and relative proportions of resistant starch, or rapidly and slowly digested starch, in foods and food ingredients.

Future research should focus on increasing the information available on starch fractions in foods and food ingredients. Scientists also should look into the effects of processing and chemical modification on the concentrations and relative digestibility of starch fractions.

Further information. George Fahey, Department of Animal Sciences, University of Illinois, Urbana-Champaign, 132 Animal Sciences Laboratory, 1207 W. Gregory Dr., Urbana, IL 61801; phone: [phone]; fax: [phone]; email: [e-mail].