Onobrychis viciifolia Scop. (Sainfoin)

Distribution and Importance of Sainfoin

Sainfoin (Onobrychis viciifolia Scop, (family Leguminoseae) is a perennial forage legume that has been grown in Europe and Asia for centuries. The most widely used common name, sainfoin, is derived from the French “saint foin” meaning holy or wholesome hay. Other common names include: holy or holy hay, French grass, everlasting grass, medick vetchling, cockshead, esparcet, or snail grass. Its botanical genus name, Onobrychis, comes from the Greek words “onos” meaning ass, and it is felt that brychis is derived from “bruchis”, a plant. This provides some insight into the value that was placed on this species because it had been noted that asses were particularly partial to sainfoin as a feed. Sainfoin grew in Russia as a forage crop over 1000 years ago and was noted in France in the 14th century, Germany in the 17th century, and Italy in the 18th century. The first introductions of sainfoin came to North America from Europe in the early 1900s, but its success as a forage crop did not occur until the 1960s when strains from Turkey and the USSR displayed the necessary adaptibility and yield to enable the development of cultivars for the Northern Great Plains and Canadian Prairies. Although North American cultivars are restricted to the species O. viciifolia, there are other species in cultivated use. O. arenaria (Kit.) DC. and O. transcaucasica Grossh. are cultivated in the USSR and China, while O. saliva Lam. is grown in Great Britain along with O. viciifolia ().

O. viciifolia is an au’totetraploid (2n = 28) which has erect, coarse, but not tough, hollow stems about 1 m in length with oddly pinnate compound leaves having 11-29 leaflets. Inflorescences have up to 80 pink flowers on a single, erect raceme and the fruit is a pod containing a single kidney-shaped seed. Sainfoin is best suited to deep, well-drained soils with a neutral pH and good moisture-holding capacity. The deep, branched taproot can penetrate the soil to a depth of 250 cm. Being deep-rooted, it is fairly resistant to drought, but does not tolerate saline, acid, or poorly drained soils. It is winter-hardy and will normally live for 3 to 5 years as a cultivated crop. Pollination occurs via honey bees, and sainfoin has been credited as one of the most important sources of honey on the European continent.

Sainfoin is highly palatable to livestock which consume it in greater quantities than grasses of similar digestibility, and prefer it to alfalfa, a legume considered as a standard of excellence in forage crops. It has also been reported that superior weight gains in beef cattle are made with sainfoin compared to alfalfa. Interest in sainfoin occurred in North America during the 1960s because of the need for a dryland forage legume and the threat to alfalfa on irrigated land by the alfalfa weevil. Sainfoin is immune to the alfalfa weevil, but its most prominent feature is that, unlike alfalfa, it is completely bloat-safe when used as a pasture forage. Even with these attributes, sainfoin is still considered a special purpose legume in Canada and the USA. The cultivars developed are winter-hardy and drought-resistant, but they are not as widely adapted or long-lived, recover more slowly after cutting limiting the crop to a basic one-cut system, and yield 10 to 20% less dry matter when compared to alfalfa. These limitations, along with a strict requirement for neutral, well-drained soils, do not allow this species to compete with alfalfa in most areas.

Although sainfoin is native to Europe and western Asia, cultivars have been successfully bred in other countries. Using the unsophisticated breeding technique of mass selection, the varieties Melrose and Nova were produced in Canada, and the varieties Eski, Remont, and Renumex in the USA. The variety Cotswold Common is grown in England and Wales, and Canadian varieties are used successfully in New Zealand. In China, sainfoin has been extensively cultivated in the northern provinces as well as in dry and semidry areas for over 30 years. It is also used as a hay and pasture crop in South Africa, South America, and is cultivated as a forage in Australia.

Condensed Tannins (Proanthocyanidins): Occurrence and Uses

The term tannin was introduced at the end of the 18th century and was originally used to define organic substances found in aqueous extracts of various plant parts. These substances were used to tan animal hides, hence “tannin” is derived from “tanning”, the process of turning an animal skin into leather, a material much more resistant to bacterial decay, heat, or abrasion. Whereas most tanning processes now use synthetic agents, the tanning chemicals used in earlier times came from the extracts of a few dicotyledonous plants, some of which are still used today. The accumulation in these plants of compounds that tan proteins is particularly high and may occur in roots, stem, fruits, pods, bark, wood, and leaves. There are two major classes of tannins: gallic or hexahydroxydiphenic  acid-derived  hydrolyzable  tannins,  and  flavan-3,4-diol-derived condensed tannins. The compounds used for tanning leather have since been found to be condensed tannins or proanthocyani-dins. Condensed tannins occur not only in plant species used by the tanning industry, but are by far the most widely distributed tannin in vascular plants occurring in horsetails, ferns, gymnosperms, and angiosperms. They are found in virtually every part of the seed plant, especially in regions of active growth.

Tannins in Folklore and Modern Medicine

Descriptions of sainfoin having medicinal properties, whether tannin-associated or otherwise, were not found in the literature. There are, however, numerous accounts linking plant tannins and folklore medicine, and some scientific studies citing substantiated evidence of the medicinal properties of these secondary compounds. Knowledge concerning the medicinal uses of tannin-containing plants has been preserved, passed on, and added to as part of the history of numerous cultures. Plant-derived beverages, decoctions, pastes, etc. are still used today as home remedies. In areas of South Carolina, particularly around Charleston, bush teas made from the bark of cherrybark oak (Querqus falcata), the leafy branches of wax myrtle (Myrica cerifera) and sweet gum (Liquidamhar styraciflua), and the roots of marsh rosemary (Limonium nashii) and trailing blackberry (Rubus trivialis), all species with a high tannin content, are taken primarily as remedies for diarrhea, colds, influenza, sore throats, and hemorrhages. Women regularly take a tea made from branch tip shoots and needles of the longleaf pine (Pinus palustris) to relieve menstrual cramps, and the tannin-rich leaves of sweet gum are chewed as a relief for sore throat and diarrhea. Blackberry wine is a very popular home beverage in South Carolina and is also a standard remedy for diarrhea. This wine contains more tannin than any other, which accounts for its medical use. In Curacao, bush teas are made from a variety of tannin-rich plants (Krameria ixina, Acacia glauca, Melochia tomentosa) and are taken regularly as daily beverages and also as tonics to “protect the kidneys”, or after over-indulgence of alcohol. Some are taken as aphrodisiacs or abortifacients, and others routinely given to children to induce sleep. In Africa, folklore medicines favor astringent, tannin-rich plants which give immediate relief for sore throats, diarrhea, dysentery, and hemorrhaging, and in northern Iran, strong, tannin-containing tea is the main remedy for diarrhea. In South America, mate, made from the tannin-rich plant Ilex paraguariensis, is used by many for medicinal purposes. As a beverage, it is claimed to improve digestion, eliminate fatigue, stimulate the muscles and nerves, and clarify the mind. Its external use is for conjunctivitis, various skin ulcers, and as a cicatrizant on gangrenous wounds.

The interest taken in folklore medicine has led to the science of pharmacognosy, a major discipline in pharmaceutic education, whereby many of the drugs used by the ancients are still employed in the same manner today. High-tannin plants such as yellow dock (Rumex crispus) and sweet pond lily (Nymphea odorata) have been used as folk medicine cancer remedies. Numerous species have been documented as having antitumor action, their activity in this regard being due to the presence of tannins, however, because they are difficult to purify, chemically unstable, and toxic, tannins hold little promise as anti-cancer agents. Tannins can cause regression of tumors already present in tissue, but with excessive use over a period of time they can also be tumor-causing in healthy tissue. A number of tannin-containing plants are used as pharmaceuticals, for example, drugs made from Krameria and Hamamelis species are employed as astringents and for the treatment of burns (); Acacia and Rumex tannins are used as demulcents, astringents, and topical agents (); and Acacia tannins are used indirectly as molluscicides to interrupt the transmission cycle of schistosomiasis. Tannins are also reported to have anti-viral characteristics. Poliovirus, herpes simplex virus, and various enteric viruses are inactivated when incubated with red grape juice and red wines containing a high content of condensed tannins.

Commercial Aspects

Plant tannins have been used commercially for centuries, and it has only been with the advancement of chemistry and plant physiology that we have been able to attribute the effects of many of the extracts used by the ancients to these secondary metabolites. The most commonly used example is the tanning of leather hides; however, tannins have been the common ingredient for the treatment of a number of maladies from headaches to constipation, all with varying degrees of success. Tannins are important in the wine and beer-making industries as well as having industrial applications such as wood adhesives and wood preservatives. The nutritional aspects of condensed tannins are growing areas of research in agriculture with the realization of their effects in forage consumption by domestic animals. Subcutaneous injections of plant tannin fractions injected into rats have produced cancerous tumors, and in human consumption, significant correlations have been found between the excessive intake of high-tannin foods (bush-tea) and esophageal cancer. Tannins are employed as specialty chemicals in a wide range of fields such as dispersants for drilling fluids, agricultural micronutrient carriers, chemical grouting systems, and additives for boiler and cooling waters. Our expanding knowledge of the pervasiveness of these compounds in such diverse areas should ensure continued research in tannins. Commercially, leather tanning remains the major use for tannin extracts. For this and other purposes, tannins are plentiful in bark, wood, and nutshells, however, the cost of extraction must be low enough to allow these compounds to compete as synthetic chemical substitutes, or to offer manufacturing processes advantages that give lower overall production costs. The more steps required to isolate, purify, and transform tannins into speciality chemicals the greater the cost of the final product. Hindrances to utilization in commercial-scale applications include difficulties in isolation and concentration due to the variety of polyflavanoids in plants and their strong association with other organic plant materials. As an example, the commercial substitution of tannin for phenol requires that the tannin be obtained through a one-step extraction process to be economically viable. These cost restrictions and the fact that condensed tannins are available in sufficient quantity from numerous species of plants make the commercial application of a labor-intensive and costly procedure such as tissue culture highly uneconomical. The worldwide abundance of plant tannins has created continual interest in their chemical utilization. Until more is known, however, regarding the structure, biochemistry, and biological significance of these substances, which may in turn lead to specific condensed tannins being required for special purposes, the advent of tissue culture as a primary commercial source of these compounds seems remote.

Conclusions and Prospects

Condensed tannins in themselves, while of interest to a growing number of researchers, do not seem to possess the economic or agronomic importance to entice large scale-up commercial operations in tissue culture with sainfoin or any other tannin-containing species. Tannins, however, have been the focus in many tissue culture studies even though protocols have been restricted to fulfill laboratory-designed, small-scale needs centering around plant breeding requirements and physiological investigations. While only a minor amount of research has been conducted in tannin-related sainfoin tissue culture, there appears to be much interest in condensed tannins in the tissue culture of other species.

An excellent review of plant tannins is given by Hemingway and Karchesy (1988), which reports on structural elucidation, biochemistry, and biological significance, the latter assuming an ever-increasing portion of tannin research. As research reveals more about specific tannin interactions within the host plant and the milieu of plants and other organisms in the surrounding environment, more efforts will be made to capitalize on those which prove to be beneficial. This may involve production of very specific compounds in a purity and amount requiring highly specialized techniques, possibly tissue culture. Tissue culture may offer a unique opportunity to study these compounds at the cellular level. The physiological processes involving tannin metabolism are largely unknown. The presence of specific cell types producing tannins with particular structures may provide a vehicle for the enhanced study of individual polymers and their effects. The emerging new technologies in genetic transformation offer the potential to utilize the genetic material responsible for the production of known, useful tannins for the benefit of agriculture and other areas as yet unidentified.