Study of the chemical composition, hydration characteristics and structure of bran of wheat, rye, oat and maize

Abstract

Due to the growing interest in healthy and qualitative food, there is an increasing interest in dietary fiber. In Europe, the average daily intake of fiber lies beneath the recommended intake. In this context, bran may be part of the solution because it is one of the most concentrated sources of dietary fiber. The objective of this study is to examine the differences in chemical composition, physical characteristics and structure of wheat-, rye-, oat- and maize bran. This information is important in the context of understanding the physiological effects of bran consumption. Commercial bran contains residual endosperm that interferes with the characterization of the botanical bran. Therefore, methods were developed to reduce the endosperm contamination with a minimal loss of non-endosperm material. The starch content of wheat bran was drastically reduced (from 24% to 2%) and a clear reduction in starch content was also obtained for rye bran (from 45% to 7%), oat bran (from 57% to 13%) and maize bran (from 62% to 2%). Chemical characterization was performed, showing large differences in composition between bran of different cereals. Oat bran had the highest beta-glucan content (17%). Maize bran was characterized by a high arabinoxylan content (43%) and a low mineral content (1%). Rye bran contained more water-soluble compounds, mainly fructan (7.5%) and water extractable arabinoxylan (1.3%), than wheat bran (3.4% and 0.6%, respectively). The bran samples furthermore differed in physical characteristics. Oat bran had the highest capacity to strongly bind water (1.7 g/g dry bran) compared to wheat bran (0.8 g), rye bran (0.8 g) and maize bran (0.9 g). Moreover, when an extract was made of the different bran samples, the oat bran extract was the most viscous. Furthermore, the water extractable content of rye (35%) and oat bran (31%) was higher compared to wheat (24%) and maize bran (13%). Also bran morphology, which was examined using cryo-SEM microscopy, was highly cereal dependent. It can be concluded that the chemical composition, the physical characteristics and the structure of wheat, rye, oat and maize bran differ markedly. Hence, their physiological effects in humans can be expected to differ accordingly.status: publishe