Oats (Avena sativa), a multifunctional crop, is nutritionally superior to many other unfortified cereals. Whole oat grains are good source of dietary fiber, especially soluble beta-glucans, protein, vitamins, minerals, and antioxidants.

Numerous laboratory and clinical studies have demonstrated that consumption of oat-based products can lower serum cholesterol levels, reduce glucose uptake, decrease plasma insulin response, and control weight through prolonged satiety (Davidson and others 1991; Braaten and others 1994; Mylkki and Virtanen 2001; Wood 2007). These physiological effects of oats are primarily attributable to the elevation of viscosity in the gastrointestinal tract (Wood 2007), caused mainly by the beta-glucans. The increased luminal viscosity may lower the reabsorption of bile acid (BA) in the ileum, thus increasing BA excretion in the feces (Drzikova and others 2005). Physical elimination of BA from the enterohepatic circulation necessitates increased synthesis of BA, consequently increasing cholesterol conversion into BA in the liver, and eventually decreasing serum cholesterol (LaRusso 1983). The elevation of viscosity also slows intestinal transit, and delays gastric emptying and intestinal absorption of nutrients, such as digestible carbohydrates, thereby reducing postprandial hyperglycemia and insulin secretion. These actions, in turn, increase satiety and promote weight loss (Mylkki and Virtanen 2001; Lazaridou and Biliaderis 2007). The pasting properties of oat flours also impact textural attributes and consumer acceptance of food product.

Because of the importance of viscosity for potential health benefits and sensory attributes, understanding the factors, which may influence the viscosity of beta-glucans, will be beneficial for developing oat-based food products with enhanced health benefits. Previous studies have demonstrated that the concentration, molecular weight (MW), and structural features of beta-glucans influence its physical properties (viscosity and solubility) (Wood and others 1994).

Different from other cereals, oats are normally consumed as a whole grain; therefore the viscosity of oat-flour slurries instead of that of beta-glucan solution alone is of particular importance. However, limited research was reported related to the factors, which impact the viscosity of oat-flour slurries. In addition, besides beta-glucan-related factors, other oat components and their interaction with beta-glucan may also impact the viscosity of oat slurries, eventually the health benefits of oat-based food products.

Oat processing (steaming and flaking), involving heat, moisture, and mechanical shear, may affect the molecular-structural characteristics of beta-glucans and the interaction between beta-glucans and other oat components, consequently the viscosity, and ultimately the health benefits of beta-glucans. However, the effect of processing on the MW, structure features, and viscosity of beta-glucans is not fully understood.

The objectives of this study were to 1) investigate the contributions of beta-glucans, starch, protein, and their interactions to the pasting properties of oat flours as measured with a Rapid Visco Analyser (RVA); 2) to evaluate the effect of MW and structure of beta-glucans on viscosities of oat-flour slurries; 3) to investigate the effect of processing on beta-glucan structural-molecular characteristics, oat-slurry viscosities, and in vitro BA binding of oat flours; and 4) to better understand the relationship among the concentration and structural-molecular characteristics of beta-glucans, viscosity of oat-flour slurries, and BA binding before and after processing.