Jan A. Delcour, Willem F. Broekaert, Christophe M. Courtin, and Hans Goesaert, Katholieke Universiteit Leuven, Laboratory of Food Chemistry and Biochemistry, Kasteelpark Arenberg 20 bus 2463, B-3001 Leuven, Belgium
The Science of Gluten-Free Foods and Beverages
Consumers are increasingly aware that their daily diet is an important determinant for a healthy life. Food products are no longer only judged in terms of taste and nutritional needs, but also in terms of their ability to improve the consumer's health and well-being. Functional foods and functional food ingredients can meet these new consumer demands. They exert a beneficial influence on body functions, improve the host's well-being and health, and reduce the risk of chronic diseases when consumed at levels that can normally be expected to occur in the diet (Ashwell, 2002). Therefore, both from a scientific and an industrial point of view, interest in functional food products and ingredients is high. Within this context, cereal non-starch polysaccharides (NSP), such as mixed-linkage β-(1,3)(1,4)-glucan (β-glucan) and arabinoxylan (AX), show great potential as health-promoting food components, in particular as dietary fibre constituents or as a source for producing prebiotic compounds.
β-glucan consists of a heterogeneous group of long, linear glucose polymers, which are present in the cell walls of cereals. In general, β-glucan is made up of repetitive cellotriosyl and cellotetraosyl units separated by single β-(1,3)-linkages, but longer units of 4–15 consecutive β-(1,4)-linked glucose residues occur as well. Barley and oats are particularly rich in β-glucan, while lower levels are found in rye and wheat (Table 1) (Åman and Hesselman, 1984). β-glucan is present in a water-extractable and water-unextractable form. A lot of research has been done on the structure, functionality and physiological effects of cereal β-glucan (for a recent review, see Lazaridou and Biliaderis, 2007). A main property of this polymer is its high viscosity-forming potential, which not only depends on its conformation, but also on its molecular weight and concentration (Lazaridou and Biliaderis, 2007). The health benefits of (soluble) β-glucan, such as reducing blood serum cholesterol and regulating blood glucose levels, have been well documented (Klopfenstein, 1988; Hecker et al., 1998; Cavallero et al., 2002; Lazaridou and Biliaderis, 2007). Moreover, the United States Food and Drug Administration (FDA) allows the health claim on the relationship between the consumption of β-glucan soluble dietary fibre (3 g/day) and a reduced risk of coronary heart disease (FDA, 1997).
In contrast to the well studied physiological effects of β-glucan, knowledge about the health benefits of AX is rather poor. However, in many cereals AX constitutes the largest NSP fraction and often exceeds the β-glucan levels in β-glucan rich cereals (Table 1). Therefore, we will focus on the potential use of cereal AX in the production of potential health-promoting ingredients. In particular, after giving an overview of AX structure and properties (see Courtin and Delcour, 2002, for an overview) and the main xylanolytic enzymes, we will discuss how AX modification/degradation using enzyme technology may result in functional food components, such as high molecular weight soluble dietary fibre and prebiotic non-digestible oligosaccharides.