Characterisation of dietary fibre in cereal grains and products : emphasis on triticale and rye

Sammanfattning: Utility of cereals is mainly defined by their composition. High content of extractable dietary fibre (DF) with retained molecular features may be desired for human consumption to derive certain benefits associated with DF. In contrast, low amount of extractable DF with degraded molecules will give higher feed value to cereals intended for animal feed. This thesis investigated the composition of DF in cereals, particularly triticale and rye products. Processing effects on extractable DF components, e.g. arabinoxylan (AX), β-glucan and fructan, were also examined. The structure of AX and β-glucan in triticale, barley and tritordium and the rheology of triticale extracts as influenced by content and extractability, molecular size and structure of AX were analysed. DF in triticale spanned a relatively narrow range (13-16%), with significant cultivar and location effects. Unfavourable growing conditions resulted in significantly lower molecular weights of AX, β-glucan and fructan in triticale. On the whole, triticale DF profile was more similar to wheat than rye. Among rye products, porridge had the highest DF content (23%) with retained molecular weight, followed by crisp breads (17.8%) and soft breads (12.6%). AX appeared to be more stable during processing, while β-glucan was more labile to endogenous enzymes. Substitution pattern of AX fragments released after enzymatic hydrolysis demonstrated less branching in triticale grown under unfavourable weather conditions. The molar proportion of cellotriosyl units of barley β-glucan had a strong positive correlation with the total content. Viscoelastic properties of triticale extracts varied between locations and cultivars. β-Glucan appeared to make a negligible contribution to triticale extract rheology, which was mainly influenced by structural features of AX rather than extractable content or molecular size. The knowledge presented here will be useful for consumers of rye products when assessing processing-generated changes in DF content and composition. The cereal industry will be able to redefine processing parameters and DF labelling based on new facts. Broad variation in DF chemistry of triticale will provide more options for farmers and feed manufacturers to select cultivars best suited for animal feed formulation.

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