The impact of processing on potentially beneficial wheat grain components for human health

Abstract

Wheat based foods, mainly in the form of bread and pasta, are staples of the human diet in many countries around the world. The dry weight of mature wheat grain is composed of 70-75% starch and around 10-14% protein, which has led to the widespread perception of wheat foods as sources of energy and protein. However, whole grains are also important sources of dietary fiber, vitamins and minerals, and contain notable levels of bioactive compounds with potential health benefits like lignans, phenolic acids, alkylresorcinols, phytosterols, folates and tocols. The prominence of wheat grain in the human diet is largely due to its versatility in being processed into diverse products like flour, semolina, and other bakery products. Processing is a pre-requisite for using cereal grains as food and obtaining end products with various unique properties that are safe and appealing to consume. Processing may also help reduce the amount of hazardous molecules potentially present in harvested wheat, such as pesticides, mycotoxins and heavy metals. Each regulated step in a processing series influences the composition and/or the physicochemical properties of the different grain components, which in turn define the technological quality and the nutritional and health promoting properties of the end product. The unique textural properties of wheat foods are largely determined by the starch and gluten proteins present in the starchy endosperm, the main constituents of white flour and semolina. The health-promoting effects of wheat-based products are mainly associated with the dietary fiber and bioactive compounds that are enriched in the grain peripheral layers, and mainly the aleurone layer, which is generally a component of the bran fraction after milling. Fractionation by milling and the way the different milling streams are subsequently recombined therefore has a considerable impact on the relative abundance of each grain component in the wheat flour/semolina and, consequently, in end products. Further processing steps, such as dough making, microbial fermentation, extrusion, and baking can also affect the relative amounts and bioavailability of grain components. Some examples of the effects of grain processing procedures on the bioavailability of important grain components in wheat foods consumed by humans will be presented in this chapter. Suggestions of how to improve these processes in light of the implications for human health will also be discussed.