Matthew C. Allan, Ph.D.
Postdoctoral Research Associate
Mauer Lab & Whistler Center for Carbohydrate Research
Department of Food Science
Purdue University, West Lafayette, Indiana

October 30, 2019 at 10:30 am
G40 Schaub Hall
NC State University

Hosted by the USDA-ARS Food Science Research Unit

With the current drive to reduce added sugars in foods, it has become apparent that replacing sugars in baked goods (e.g., cakes and cookies) is a challenge because sugars greatly influence the physiochemical properties during and after cooking. Therefore, the effects of sugars on starch gelatinization (cooking) and retrogradation (post-cooking) were needed to better understand the structure-function and effectively reduce added sugar. The gelatinization temperature of starch increases in the presence of low molecular weight carbohydrates, such as sugars and sugar alcohols. The sweeteners diffuse into the amorphous regions of the starch granule where sweetener-starch interactions stabilize the amorphous regions and require a higher temperature to gelatinize. Sugars and sugar alcohols with a greater number of equatorial and exocyclic hydroxyl groups, molecular flexibility, and molar volume tended to increase the gelatinization temperature to a greater extent due to stronger sweetener-starch interactions that stabilized the amorphous regions of the starch granule. It was also found that sweetener stereochemistry affected starch retrogradation. Sweeteners with a greater propensity to form intermolecular interactions were more effective at slowing retrogradation at low concentrations, but with increasing sweetener concentrations, the sweeteners then promoted retrogradation. Systems where retrogradation was delayed, sweeteners interfered with amylopectin-amylopectin interactions, while systems where retrogradation was promoted, the sweeteners were competing for the water and/or forming H-bond bridges that promoted retrogradation. Thus, sweeteners with greater molar volume, molecular flexibility, and stronger intermolecular interactions, such as sugar alcohols, increased the gelatinization temperature more and were conducive to promoting retrogradation. Whereas, smaller, relatively rigid sweeteners that form weaker intermolecular H-bonds, such as 5-carbon sugars, increased the gelatinization temperature the least and tended to inhibit retrogradation. With a better understanding of how sugars affect gelatinization and retrogradation, suitable replacements can be explored.