International Dietary Fibre Conference (DF12) location:Rome, Italy date:7 - 9 May 2012
Grains, all belonging to the family of the grasses or Graminaceae, typically have hemicellulose type cell walls which are rich in arabinoxylans (AX) and mixed-linkage β-glucan. However, different grain types and tissues are known to differ strongly in the relative amounts of AX and β-glucan in their cell walls. In this study, the location of AX and β-glucan in cell walls of wheat, barley, oat and rye was investigated by microscopic analysis. AX and β-glucan were stained with different techniques, i.e. AX staining with a fluorescently labeled xylanase probe, β-glucan staining with Calcofluor and immunolabeling using monoclonal antibodies against AX or β-glucan. The staining methods were complementary to each other in revealing the location and distribution of the major cereal dietary fiber components in the different grains. AX was mostly concentrated in nucellar epidermis and aleurone cells, whereas β-glucan was concentrated more in subaleurone cells. Furthermore, in the case of barley and rye, the endosperm cell walls also contained high amounts of β-glucan. Interestingly, β-glucan in rye and barley endosperm cell walls was located adjacent to the cell contents, suggesting that it is not evenly distributed in the endosperm cell walls. The results give new insight into the structure of the cereal dietary fiber complex. Further development of microscopic techniques will help in elucidating the cereal cell wall structure even in more detail.