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 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.

The Chemical Composition of Rye, Wheat and Oat

Component % of dry matter
Rye 100 Wheat 100 Wheat 66 Oat Groat
Protein
Fat
Starch
Ash
Total dietary fibre
of which soluble fibre
8-13
2-3
56-70
2
15-17
3-4
12-14
3
67-70
2
10-13
1-2
13
1
84
0,5
3
1-2
13-16
6-7
54-64
2
11-13
3-5

(man et al. 1997, Clydesdale 1994, Lasztity 1998, Hrknen et al. 1997, Nilson et al. 1997a,b, 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
b-glucan content. b-glucan 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, man 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.

Nutrient Amount in 100g Rye Bread % RDI (for women) % RDI (for men)
Vitamin E
Thiamin
Riboflavin
Niacin
Folate
Iron
Zinc
Selenium
Calcium
Potassium
Magnesium
fibre
1,0 mg tocoph.
0,18 mg
0,2 mg
1,2 mg
43 g
2,7 mg
2,3 mg
3,2 g
31 mg
0,4 g
75 mg
9,9 g
14
16
15
8
14
18
33
8
4
13
27
40
10
13
13
6
14
27
26
6
4
11
21
40


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, Pealvo 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 g/100 g), PIN (381 g/100 g), LAR (324 g/100 g) and MED (148 g/100 g) (Pealvo et al. 2005). The SECO and MAT are the minor lignans (38 g/100 g and 27 g/100 g respectively) (Pealvo 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 in Rye


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