David G. Stevenson and George E. Inglett, National Center for Agricultural Utilization Research, U.S. Department of Agriculture, Agricultural Research Service, Peoria, Illinois, U.S.A.
OATS: Chemistry and Technology, Second Edition
Pages 321-332
DOI: https://doi.org/10.1094/9781891127649.015
ISBN: 978-1-891127-64-9
Abstract
In the United States, for 2003, the American Heart Association reported that 71.3 million people had at least one form of cardiovascular disease (CVD), causing 911,614 deaths. This was 37.3% of mortality from all causes, making CVD the single leading cause of death. Diabetes, which is also increasing, was responsible for 73,249 deaths in 2002 (Hedley et al 2004). Increases in both CVD and diabetes are correlated with the rise in incidence of obesity; 80% of type 2 diabetes and 70% of CVD are related to obesity. In 2002, 28.1% of men and 34.0% of women in United States were obese (Hedley et al 2004).
In many industrialized nations, urbanization, which is conducive to poor diet choices and insufficient exercise, has led to an alarming increase in the incidence of various health disorders. Additionally, CVD and diabetes are increasing in the world's two most populous countries, China and India (Popkin et al 2001, Rajeshwari et al 2005). Globally, the dramatic increase in the incidence of diet-related health disorders is placing great pressure on governments to identify and implement dietary intervention programs. Development of functional food ingredients will play an important role in alleviating the prevalence of these health disorders.
Functional foods are generally defined as foods that provide health benefits beyond basic nutrition when consumed on a regular basis at effective levels (Hasler et al 2004). The biologically active components or dietary supplements incorporated into functional foods impart health benefits or desirable physiological effects.
Recently, as interest in functional foods has grown, several processes have been developed to fractionate oat groats to produce functional food ingredients such as oat bran. Such functional components have become attractive because of increased awareness of the health benefits associated with the consumption of soluble fibers. This has created a strong market for products containing dietary fibers. Numerous studies (see Chapter 12) have demonstrated the association between consumption of whole-oat and oat-bran products and 1) reduction of serum cholesterol (de Groot et al 1963, Anderson and Chen 1986, Mälkki et al 1992, Ripsin et al 1992, Uusitupa et al 1992, Behall et al 1997, Pomeroy et al 2001) and 2) attenuation of blood glucose and insulin levels (Wood et al 1994, Pick et al 1996, Tappy et al 1996, Reyna et al 2003, Prosise et al 2004). The ability of soluble fiber from oats to lower heart disease risk was recognized by the U.S. Food and Drug Administration (FDA) when it authorized a health claim (FDA 1997) based on soluble β-glucan fiber content (see Chapter 13). The health benefits are dependent on consuming a sufficient quantity of oatmeal or oat bran over an extended period. Increased use of dietary-fiber-rich oat products in food applications would enable sustainable consumption of oat soluble fiber and thereby help reduce the incidence of CVD and other diet-related diseases.
Other oat components, such as the pentosans and cellulosic fractions, may also have the health benefits expected of dietary fiber (Chapter 12). Although no specific FDA-approved health claims exist for insoluble dietary fibers, observational studies indicate reduced risk of heart disease and diabetes at higher consumption levels (Salmerón et al 1997, Wolk et al 1999), and health professionals recommend that most people need to increase their consumption. This fact and the ready availability of oat hulls has led to the development of several processes to produce ingredients from oat-hull fiber.
Several technologies can economically produce enriched or enhanced dietary fiber ingredients from oats. The resulting ingredients facilitate incorporation of oat soluble or insoluble fiber into food products and provide greater opportunities for consumers to adopt healthier diets.
Commercial products have utilized several types (or classes) of processing methodologies. Many are at least partially based on classical milling techniques: dry-milling processes are used to produce a fraction with increased β-glucan content, which serves as the starting material for subsequent enrichment. Essentially, as in wheat milling, such steps are designed to separate the outer bran layers from the starchy endosperm flour. Commercial wheat bran is typically about 25–30% of the kernel, whereas the definition for oat bran adopted by the American Association of Cereal Chemists (now AACC International) in 1989, and subsequently by the FDA (1997), requires that it not be more than 50% of the kernel. Unlike with wheat, steps such as the kilning system described in Chapters 9 and 14 are used to inactivate lipase and/or otherwise stabilize the product so that the lipids are not oxidized, which is essential for a marketable shelf life. Other heat-stabilization options include fluidized beds and extrusion cooking. Also unlike wheat, commercial oat varieties are harvested with an attached hull, which, in traditional milling, is removed and not used for food. However, more recent technologies have developed the oat-hull fiber as a food ingredient. Some methods involve solubilization of the β-glucan, followed by partial or total fractionation of the soluble and insoluble material, perhaps employing some specific isolation step, such as precipitation by solvent.
This chapter reviews the processes developed to produce oat-based functional food ingredients, with special emphasis on those with enhanced health benefits. The processes discussed in the following sections have been divided into six groups based upon the fractionation methodology utilized. The first five, involving soluble fiber, are dry-milling operations, organic-solvent extractions, aqueous extractions, enzyme processes, and extraction methods utilizing acid/base conditions or temperature. The last is for cellulosic-based oat fibers. In addition to the process descriptions, information is provided on the functionality and applications of the end products.
It is important to note that, in a few instances, nutritional trials conducted with these products have indicated that the expected health benefits are diminished or absent. It is beyond the scope of this review to theorize reasons for individual discrepancies. However, readers should keep the following points in mind when evaluating the nutritional study data. First, oats contain very active β-glucanases that can dramatically alter both the solubility and molecular weight of the oat soluble fiber when the fiber is exposed to aqueous environments. Ingredients developed from inadequately heat-stabilized oats are at risk for undesirable enzymatic modifications. Second, management of the drying and recovery process is critical. Using excessive heat during drying or drying to an excessively low moisture content may result in the removal of significant amounts of bound water, which can dramatically affect hydration properties. Overdried products do not fully hydrate and thus may exhibit reduced functional attributes.
