CHEMICAL COMPOSITION OF RYE
Down to the Molecular Level: What is Rye Composed of?
A rye kernel contains large amounts of
important dietary fibre components combined with other bioactive compounds, which have
numerous positive functions for our health and well-being. Rye contains both soluble and
insoluble dietary fibre. The main dietary fibre component in rye is the partly soluble arabinoxylan.
In bread making, the cell wall polysaccharides in rye have a profound effect on the
rheological properties of dough and bread.
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 Chemical Composition of Rye, Wheat and Oat
The comparison between the chemical compositions of rye, wheat and oat grains are shown in
the table below. All of these cereals are presented with an extraction rate of 100, which is
comparable to whole grain or whole grain flour. The composition of wheat is also presented
with an extraction rate of 66, which corresponds to white wheat flour. In Finland and
Denmark, rye flour generally means whole grain rye with an extraction rate of 100 or close
to it. In Sweden and Norway the most commonly used rye flour has an extraction rate of 80
or close to it.
% of dry matter
Total dietary fibre
of which soluble fibre
(Åman et al. 1997, Clydesdale 1994, Lasztity
1998, Härkönen et al. 1997, Nilson et
Welch 1995, Andersson et al. 1993, Vollendorff and Marlet 1991 and
Hansen et al. 2004)
The number after the name of the cereal indicates the extraction rate.
Extraction rate is the proportion of flour derived from a known quantity of grain.
Extraction rate 100 = whole grain flour.
Extraction rate 66 = 66% of grain is milled in this flour.
Due to differences in analyzing methods the values are not totally comparable.
There are two types of dietary fibre, soluble and insoluble. Water-insoluble dietary fibre
includes e.g. cellulose, and lignin, whereas xylans and
b-glucan are partly insoluble, partly soluble. Soluble fibre, such as
arabinoxylan and b-glucan, forms a
viscous gel already at very low concentrations (0.5-2%). Rye contains more arabinoxylan
and mixed-linked b-glucan than
wheat, but similar amounts of cellulose and lignin.
Oats are widely known for their high
has been shown to have a positive effect in reducing the risk of coronary heart disease. Whole-grain rye contains remarkable amounts of soluble arabinoxylan, which seems to have
positive health effects similar to the
b-glucan in oats.
The dietary fibre
content of typical rye bread is about three times higher than that of white wheat bread.
The reason for this is that rye bread is usually made of whole grain rye flour, while
white wheat bread is typically made of wheat flour, where the outer layers of wheat grain
have been eliminated during the milling process. However, even at the same extraction
rate, rye flour would have a higher fibre content than wheat flour.
The outer layer of the endosperm, the aleurone layer, is rich in proteins, minerals and
vitamins, especially B-vitamins. Rye is an especially good source of several minerals,
e.g. manganese, iron, copper, zinc, selenium, magnesium and fluoride. The aleurone layer,
i.e. the part of the grain very close to the surface, is difficult to separate from the
bran (Clydesdale 1994, Åman et al. 1997).
Mineral and Vitamin Content of Rye Bread and the Percentage of Recommended Daily
Intake (RDI) that 100 grams (3 slices) of Whole grain Rye Bread Provides.
||Amount in 100g Rye Bread
||% RDI (for women)
||% RDI (for men)
|1,0 mg tocoph.
Rye grains are also a good source of non-nutrient diphenolic lignans.
It was long assumed that matairesinol (MAT)
and secoisoresinol (SECO) are the main plant lignans. Recently new
lignans, pinoresinol (PIN), medioresinol (MED), syringaresinol
(SYR), lariciresinol (LAR) and isolariciresinol (ISOLAR) have been
found in rye comprising over 90% of total lignan content of rye
(Heinonen et al. 2001, Peñalvo et al. 2005).
Lignans have been shown to be concentrated in the outer layers of the kernel (Nilsson et al.
1997 a,b; Liukkonen et al. 2003). Most abundant lignans in whole grain rye are SYR (973
and MED (148
et al. 2005).
and MAT are the minor lignans (38 µg/100 g and 27 µg/100 g
(Peñalvo et al. 2005).
In the gut, the
intestinal microflora converts the plant lignans into their mammalian derivatives,
enterodiol and enterolactone, which may have a number of biological properties significant
to human health. Of the new lignans all, except isolariciresinol, are converted to
enterolactone and enterodiol (Heinonen et al. 2001). Rye grains also contain polyphenols,
e.g. tannin (antioxidant which inhibits the
activation of chemicals to mutagenic and carcinogenic derivatives and hastens chyme
passage), phytic acid and vitamins and minerals (Adlercreutz and Mazur 1997). Ferulic
acid is the major phenolic acid in rye, contributing to the antioxidative effects of rye
(Andreasen et al. 2000, 2001).
Alkylresorcinols are phenolic lipids that occur in rye at
concentrations of 30-150 mg/100 g dry matter (Ross et al. 2003).
Structures of Plant Lignans Identified
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