Dietary fibre plays an important role in health and has been linked to prevention of heart disease and cancer, as well as protecting against obesity. Many of its health effects are a result of the microbial fermentation of dietary fibre in the large intestine, notes author Sirpa Karppinen from VTT.
While the macronutrients in rye are the same as in other cereals - starch, dietary fibre, and protein - rye generally contains less starch and crude protein than wheat, but more free sugars and dietary fibre. Of the free sugars, sucrose and fructo-oligosaccharides dominate.
The researcher studied the effect of solubility and processing on the fermentability of rye bran from different rye bran fractions. Before fermentation, substrates were enzymatically digested simulating conditions within the small intestine in order to remove starch and protein. Fermentability was studied in vitro.
Three groups of dietary fibre polysaccharides were identified - fermentable, soluble polysaccharides that are rapidly fermented; fermentable cell-wall associated polysaccharides that are gradually released from the cell-wall matrix and then fermented; and polysaccharides and cell-wall structures that are not fermented at all.
The process led to production of short-chain fatty acids, which was related to the consumption of carbohydrates: the higher the rate and quantity of carbohydrate consumption the higher the rate and quantity of the fatty acid production. Butyric and propionic acids were produced in all rye fermentations, according to Karppinen.
The partly soluble fibre arabinoxylan was found to be fermented in vitro by Bifidobacterium longum, a dominant Bifidobacterium species in the adult human colon. Arabinoxylan may have positive health effects similar to another soluble fibre, beta-glucan, found in high quantities in oats. Beta-glucan has been shown to help reduce the risk of coronary heart disease. Rye could therefore be considered a candidate prebiotic.
Rye is also rich in plant lignans. Intestinal microflora in the gut converts plant lignans into their mammalian derivatives, enterodiol and enterolactone, which may have a number of biological properties significant to human health. Fermentation of carbohydrates also had an impact on this conversion process, reports the author.