Carbohydrate Research and Metabolomics: Current Projects
Starch Digestibility and Chemistry
Starch has unique chemical and physical characteristics among other carbohydrates. It occurs naturally as distinct particles, called granules. Those granules are insoluble, relatively dense, and hydrate only slightly in room-temperature water. The other uniqueness of the starch is that most starch granules are a mixture of two sugar polymers: a highly branched polysaccharide named amylopectin, and a basically linear polysaccharide named amylose. The semi-crystalline properties of native starch are related to the short-chain fraction of amylopectin arranged as double helices and packed in small crystallites. Starch is the only polysaccharide that humans can digest. Due to high rates of over-weight population (especially childhood obesity), there has been elevated attention to starch digestibility, which is governed by botanical source, structure of food matrix and fine structure of starch molecules. Physical and chemical starch modifications can alter the digestibility of starch. The starch is classified in three categories depending on the rate and extent of digestion as rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS). In one of our studies, we investigated the effect of cooking and chemical modification of physicochemical properties of starch including their digestibility. Our results showed that, acetylation and oxidation can alter the digestion rate. However, there is more research needed to investigate the starch digestibility that is affected by food matrix, especially in whole wheat products.
Food and Health
Plant derived non-starch polysaccharides which include dietary fibers have many beneficial properties such as decreasing the risk for type 2 diabetes mellitus (T2D), cardiovascular disease, and colon cancer. However, the role of dietary fiber on inflammation is an important area that needs further exploration.
Immune system consists of the molecules, cells, tissues and organs that function together to provide immunity to the body. Epithelial barriers, phagocytic cells, natural killer cells, the complement system and cytokines play a vital role in maintaining immunity in the body. Among other epithelial barriers, intestinal epithelial cells are exposed to a plethora of molecules that are present in the diet. As part of the innate immune system, intestinal epithelial cells exhibit the ability to recognize antigens through pattern recognition receptors such as Toll-like receptors (TLRs), produce cytokines and chemokines, and act as nonprofessional antigen-presenting cells. Thus, intestinal inflammation is a natural and protective function of the gastro-intestinal tract which helps maintain the health of the individual. However, deregulation of this inflammatory response can lead to detrimental effects such as inflammatory bowel disease (IBD), the collective name for Crohn’s disease and ulcerative colitis. The disease is characterized by strong and unpredictable inflammatory attacks in the intestine. It affects as many as 1.4 million persons in the United States and about 2.2 million persons in Europe. Due to the chronic inflammation associated with the disease, these patients are at a higher risk of developing colon cancer. Dietary substances that exhibit immunomodulatory properties could be beneficial in regulating the intestinal inflammation that lead to diseases such as IBD. Dietary polysaccharides are one such group of substance that can impact inflammation.
Research has indicated several polysaccharides to have immunomodulatory properties that could attenuate inflammation. Studies suggest that in the gut, dietary fibers such as arabinoxylans or β-glucans could be taken-up by M-cells, or by extensions from intestinal macrophages and dendritic cells, and cross the intestinal mucosa. These data suggest that dietary fibers could modulate the activation of immune cells in the gut by directly interacting with them in the lamina propria.
However, dietary polysaccharides are complex molecules that could have different structural features such as type of sugar molecules that constitutes the polysaccharide back bone, substituted sugar molecules and phenolic groups, etc. Previous research has indicated that polysaccharides have a structure-function association for immunomodulatory properties. Polysaccharides that are generally identified by the same name could have different fine structural properties based on the botanical source. For example, arabinoxylan from maize has a more complex structure compared to arabinoxylan from wheat. Maize arabinoxylan has more ferulic acid attached to it compared to wheat arabinoxylan. These findings indicate that it is prudent to explore each of these polysaccharides based on their source, rather than categorize them as one entity.
Whole grain cereals are a rich source of dietary polysaccharides. The main non starch polysaccharide found in cereal grains is arabinoxylan. It is generally considered as a dietary fiber and has been shown to have many health benefits including anti-inflammatory activities, cholesterol lowering activity, attenuation of type 2 diabetes, enhanced absorption of certain minerals, fecal bulking, and prebiotic effect, etc. Arabinoxylan extracted from wheat bran has been shown to have potent effects on innate and acquired immune response in mice bearing S180 sarcoma tumors. In these studies, the authors showed that treatment with arabinoxylan resulted in increased phagocytic activity of tumor-bearing mice macrophages and increased activities of B- and T-cells. Thus, it has been suggested that arabinoxylan extracted from wheat bran by alkaline or enzymatic procedures could be a good source of natural immunomodulation. Arabinoxylan have been associated with beneficial health effects in patients with impaired glucose tolerance. Thus, arabinoxylan have the potential as immuno-enhancing and antioxidant additives in functional foods. Also, there is some limited research on the anti-inflammatory activity of arabinoxylan, and most of the current work focuses on the ferulic acid and phenolic compounds associated with arabinoxylan. There is a need for additional work on the anti-inflammatory properties of arabinoxylan. However, many of the research exploring the biological effects of arabinoxylans have not taken the effect of fine structural properties of the molecule into consideration. Considering the fact that the inflammatory property of arabinoxylans is associated with the fine structural details of the molecule, it is important to recognize the role of each fine structural details of the molecule to its resulting inflammatory properties.