Phytochemicals

Rye contains lots of phytochemicals which are suggested to impact our health. The knowledge on this field is growing fast. Among the most studied rye phytochemicals are lignans and alkylresorcinols, less is still known of benzoxazinoids, phenolic acids, phytosterols and tocols in rye.

Lignans

Lignans are phenolic compounds that can be found in many plants. Of all grains consumed, lignans are most abundant in rye, the two most common lignin types in rye being syringarecinol and pinorecinol. Lignans are concentrated on the outer layers of the grain and many of them are converted in the large bowel to enterolactone, which is the metabolite circulating in blood. Both plant lignans and enterolactone are excreted in urine in the conjugated form and in faeces mainly in the free form. Intake of rye bread has been shown to increase blood enterolactone levels. In contrary antibiotic intake, obesity and smoking are associated with low enterolactone levels.

Enterolactone is classified as phytoestrogen, being able to bond to the estrogen receptors in the body. In an animal study rye bran has shown to affect estrogen signaling and in a cross over trial rye diet is shown to increase the enterolactone levels in serum and urine in human.

Lignans seem to have several positive health effects, e.g. high lignan intake especially from rye products may protect agains certain types of cancer, such as hormone dependent breast and prostate cancer. The mechanisms behind these effects are still unclear.

Alkylresorcinols

Alkylresorcinols are phenolic lipids present in the outer parts of rye and wheat kernels. Relatively little is known about the metabolism of alkylresorcinols. Human subjects absorb alkylresorcinols in the small intestine via the lymph system and they are circulating bound to the lipoproteins. After wheat-bran and rye bread diets human urine has been shown to contain two metabolites, 3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-1-propanoic acid (DHPPA), but very small amounts of unchanged alkylresorcinols supporting the hypothesis that alkylresorcinols are metabolised in humans via ß-oxidation of their alkyl-chains. It is also known that when the intake of alkylresorcinol is regular and voluminous, alkylresorcinol are stored in adipose tissue.

In animal research alkylresorcinols are considered to be inhibitory components responsible for lowering feed intake and growth rate. Furthermore, alkylresorcinols have been shown to have many biological activities, including antimicrobial, antiparasitic, antitumour and antioxidative effects. The effects are possibly specific for different carbon chain lengths of alkylresorcinols. Rye alkylresorcinols have been shown to decrease oxidation of LDL particles in in vitro experiments.

Because alkylresorcinols are present in high amounts in whole grain wheat and rye but not in appreciable amounts in other foods, alkylresorcinols and their metabolites serve as novel biomarkers of wholegrain intake. The intake of wholegrain rye and whole grain wheat can as well be separated from each other by comparing the ratio of alkylresorcinol subgroups present in plasma.

Benzoxazinoids

Benzoxazioids are alleochemicals which plants use for stress signaling. Whole grain rye and wheat are known to be the main sources of benzoxazinoids in human diet. Differing from other bioactive compound of rye, benzoxazinoid are mainly located in the germ of the grain. In rye the most abundant benzoxazinoid is DIBOA (2,4-dihydroxy-1,4-benzoxazin-3-one) and other subgroups are known to exist, too. Benzoxazinoid are proved to be found in processed rye products although the amount and distribution of different benzoxazinoids can change during processing.

It is known that benzoxazinoids can be absorbed from the intestine, but quite little is yet known of their metabolism and function in the body.

Phenolic acids

Phenolic acids derive from benzoic acid and cinnamic acid. The most abundant of these in rye are cinnamic acid derivates ferulic acid and sinapinic acid. 90 percent of phenolic acids are bond to the arabinoxylans in the outer layers of grain but free ferulic acids are found as well both in outer and inner layers of the grain.

Processing, eg. fermentation, increases the absorption of bond phenolic acids. Because fermentation is typical for rye baking, phenolic acids in rye products are quite well absorbed.

In vitro studies have shown antioxidative properties of ferulic acids and they are proposed to be one link between rye consumption and lowered risk of cardiovascular disease, diabetes and cancer. Although there is slight evidence on the connection between phenolic acid content of rye bread and glucose and insulin responses after ingesting it, solid proof on health effects of phenolic acids is still lacking.

Phytosterols

Phytosterols are steroid alcohols from plant origin. In grains they are either in free or conjugated form. Phytosterols regulate plant cell membrane solubility and take part for example in different transportation and storage functions.

Phytosterols can be found in all layer of grain but their concentration increases with the fibre content so most abundant they are in the bran.

Phytosterols in high amounts can be used to reduce elevated blood cholesterol levels. The dose should be at least 2 g/d, which cannot be reached by only diet rich in rye but regular consumption of rye can increase the total amount of phytosterols in the diet and therefore it can help reaching the needed level for the health effects.

Tocotrienols and tocoferols

Tocotrienols and tocoferols are tokols, antioxidative components that possess vitamin-E activity. The most abundant tocols in rye are α-tocotrienol and α-tocoferol. Like most of the other bioactive compound, tocols are located in the outer parts of the rye kernel. The tocol content varies with the variety, growth site and timing. The amount of tocols is comparable with other grains, such as wheat and barley. Processing decreases the amount of tocols but despite this whole grain products are relatively good sources of tocols.

In in vitro studies tocols have improved the function of endothelial cells, regulated inflammation reactions and cell survival. In one large cohort study high α-tocoferol content of plasma decreased the risk of death in cardiovascular causes, cancer and other causes.

 

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