Carbohydrate quality of barley products with focus on β-glucan

Barley (Hordeum vulgare L.) has a high content of dietary fibre and especially of mixed-linkage (1→3),(1→4)-β-D-glucan (β-glucan). It is well documented that a high intake of dietary fibre promotes beneficial health effects e.g. lower risk of type II diabetes and cardiovascular disease. β-Glucan in oats and barley even has an approved EFSA health claim for maintaining normal blood cholesterol levels. Cereals are usually processed before consumption and it is therefore important to study not only raw materials, but also how they are affected by processing. \n \nSix barley varieties with different starch and dietary fibre content and composition were followed from kernel via sifted flour to two products: extruded breakfast cereal and bread. The starch and dietary fibre content and composition were analysed in each step to determine how processing affected each variety. The difference between kernels and sifted flour was large, as expected since the outer part of the kernel containing mostly insoluble dietary fibres was removed. The varieties were affected mostly in the same way and differences in kernels were observed also in sifted flours. \n \nExtrusion increased the extractability of arabinoxylan and β-glucan while decreasing the molecular weights and the contents. The molecular weight of arabinoxylan of one variety (SW 28708) was less affected by extrusion than the other varieties while another variety (KVL 301) had a considerably lower extractability of β-glucan in the extruded product than the other varieties. \n \nBread baking also increased the extractability of β-glucan and arabinoxylan while decreasing the molecular weights. There was however one variety (SLU 7) that maintained a higher molecular weight of β-glucan. Since molecular weight reduction during baking is a known problem this was studied further. The β-glucanase activity was similar in sifted flour of all barley varieties, but higher for the wheat flour used in this study. This implied that differences in β-glucan breakdown depend on structure or some inhibitory factor in SLU 7. Incubation with water in 37 °C also gave lower breakdown of β-glucan in SLU 7 compared to other varieties. β-Glucan generally consists of 90% cellotriosyl and cellotetraosyl units but the ratio between them was different for SLU 7 than for other varieties, which could be part of the explanation for the differences in β-glucan breakdown.