Structural and Functional Properties of Enzymatically Modified Slow Digesting α-Glucans
Abstract
Moderating glycemic response to foods is important for the potential to control or prevent hyperglycemia-related diseases, such as diabetes and cardiovascular disease. The importance of slowly digestible carbohydrates (SDC) lies in their health effects: moderated blood glucose response, and a potential for increased satiety and reduced intake, and weight management. The research presented is on structural properties of novel, mostly soluble, α-glucans (glucosecontaining oligomers and polymers with different linkage types and combinations) that are required for slow yet full digestion, and how they behave in food systems. Up to this point, little has been known regarding what structural properties of glucose-containing carbohydrates result in slow digestion, although starch structure has been well investigated and it is known that raw starch has a slowly digestible property. In addition to the structure-function aspect of the thesis work, this research contributes information about how α-glucan SDCs can be incorporated into food products that undergo heat treatment in the presence of moisture. The α-glucans maintain their SDC property while raw starch is gelatinized and becomes rapidly digestible. The rate of hydrolysis of a large number of novel α-glucans was studied using a simulated upper gastrointestinal in vitro digestion utilizing porcine pancreatic α-amylase and α-glucosidases from the rat intestine, and a subset was then evaluated in a crossover design clinical trial with blood glucose monitoring. Linkage and molecular weight analysis using gas chromatography of partially methylated alditol acetates and multi-angle light scattering and refractive index (MALS-RI) detection at time points during in vitro digestion were used to elucidate the relative rate of digestion of different linkage types in new and known α-glucan carbohydrates. Clinical results showed that resistant maltodextrin and reuteran had low initial glycemic profiles with no extended digestion, indicating rapid and resistant fractions; dextran and raw wheat starch had low initial glycemia and extended profiles, indicating a true SDC property; isomaltooligosaccharides and alternanooligosaccharides had high glycemic profiles; and alternan, as a larger polymer, was essentially undigested with a flat at-baseline glycemic profile. It was found that larger molecules with α-1,6, 1,3, and 1,2 linkages are generally more slowly digestible, though not always fully hydrolyzed within a 6 h upper GI in vitro digestion. Static and dynamic light scattering (SLS and DLS) showed the dextran sample to have a secondary structural conformation of branched or associated coils, and the Kratky plot confirmed this finding, indicating a molecular configuration of polydisperse coils likely contributing to a slow digestion rate. Rheological, turbidity, and SLS and DLS analyses were used to examine ingredient interaction between novel, enzymatically-modified α-glucans with slow digesting properties found most promising for inclusion in food products. A model nutritional beverage system was utilized containing proteins and salts. It was found that solvent and ion concentration of solutions were important for dictating aggregation formation with highly branched alternans and oligosaccharides in solution alone, or in the presence of soluble protein aggregates. Further, salts in solution proved to influence rheological and turbidity measures of all four α-glucans examined in the model system, indicating they may affect aggregation and structural conformation of such large carbohydrates. However, only tapioca maltodextrins showed in vitro rate of digestion affected by aggregation.
Degree
Ph.D.
Advisors
Hamaker, Purdue University.
Subject Area
Nutrition|Medicine|Public health
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.