The dietary fibre content of rye is the highest among common cereals. Typical rye bread contains about three times more fibre than white wheat bread mainly because the starchy endosperm of rye contains twice as much cell wall components than wheat. Also, rye is typically used as whole grain unlike wheat.
The main components in rye fibrer are arabinoxylan, (7.5-10.3%), fructan (3.6-4.6%), β-glucan (1.4-1.5%), cellulose and resistant starch (2.6-3.5%). Depending on definition also lignin and some other compounds attached to fibre complex of rye are included into the fibre fraction. Therefore the total amount of fibre can vary in different sources, being 15-24 % of dry matter.
Fibre, especially arabinoxylan, content and solubility influence the breakdown of starch, softness and aging of rye products. On the other hand during food processing, such as baking, the dietary fibre content may change. Common changes include an increased content of resistant starch and reduced content of soluble fibre components, such as fructan, β-glucan and arabinoxylan. Sourdough and yeast fermentation result a significant degradation of the rye fructan. Arabinoxylan retains relatively well high molecular weight in bread making process, contrary to β-glucan. The crisp breads produced without yeast have the highest dietary fibre and fructan contents. During porridge making and bread baking the content of total dietary fibre is increased (from about 20% to 23% of dry matter) due to formation of resistant starch. The molecular weight of extractable fructan and arabinoxylan remains stable during porridge making. However, incubation of the rye flour slurries at increased temperature resulted in a significant decrease in extractable arabinoxylan molecular weight. The baking-method-dependent change in content and molecular weight of extractable dietary fibers may be of significant importance for the nutritional and technological properties of the rye dietary fiber.
Besides fibre, the so called rye dietary fibre conmplex contains associated bioactive components, such as phenolic acids, cinnamic acids, alkylresorcinols, lignans, sterols, vitamins and minerals.
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