Gallnut

Plant galls are abnormal growths (plant excretion) of plant cells formed as a response to insect's (such as the gall wasps of the Cynipidae family) burrowing into the bark and laying eggs. The eggs are ussualy laid in the leaf or stem in the spring, before leaves are fully developed. The immature insects can often be found in a cell or cells within the developing gall. After a brief period of cell growth, gall development stops. The insect becomes enclosed by the gall and feeds only on gall tissue during its development. Small holes on the outside of the gall indicate that the adult insects have emerged. If galls are cut open the larvae, pupae and adults may be observed; providing they have not previously emerged. These growths may also be the result of fungi, bacteria, nematodes or mites, but insects are the prime cause. Gall-forming insects include aphids, phylloxerans, psyllids, midges (gall gnats) and cynipid wasps (gall wasps). The gall wasps (order Hymenoptera, family Cynipidae) are the most important insects that induce plant galls. These wasps are very small and, all but a few species, are less than 1/4 inch in length. Color varies greatly. Some species are black, others are red, yellow or amber. The larvae are legless and both larvae and pupae are white in color.

These growths are called galls because they contain large amounts of tannin which has a very bitter taste. They are known as gallnuts because they tasted as bitter as gall. Galls vary widely in size, shape, texture and color. It is not uncommon to find several different species on the same woody plant or tree. A major commercial source of medicinal gallnuts is oak trees, which yield the herb moshizi, but a similar material is found on sumac (Rhus species), produced by the activities of a type of aphid; these galls are called wubeizi by herbalists. The plant secretes the liquid gall, comprised mainly of tannins, that hardens to become the "nut." Gallnuts are a native product of Southeast Asia, China, but are also produced in small amounts in Turkey, India, Japan, and Korea. Galls occur on a wide variety of woody plants.

Sumac Gall                           Oak Gall

Gallnuts from oak and sumac contain the highest naturally occurring level of tannin (gallotannin): 50-75%. They also contain 2-4% each of the smaller molecules gallic acid and ellagic acid that are polymerized to make tannins. The tannin of gallnuts has been used for centuries for tanning of leather (a process involving coagulating proteins) and inks. Now, gallnut extracts are widely used in pharmaceuticals, food and feed additives, dyes, inks, and metallurgy. Gallotannin (comprised of molecules of gallic acid attached to a central glucose) is obtained from natural gallnuts by extraction with hot water; gallic acid is obtained by the hydrolysis of tannic acid with sulfuric acid. When heated above 220°C, gallic acid loses carbon dioxide to form pyrogallol; other chemicals in demand, such as propyl gallate, octyl gallate, dodecyl gallate, syringic acid, and trimethoxybenzoic acid, can all be made from gallnuts.

There are additional sources of these desired components. Since 1989, manufacturers of gallnut products began using tara (spiny sappan; Caesalpinia spinosa) imported from Peru for production of gallic acid. While sappan heartwood (from Caesalpinia sappan) is used in medicine as a blood vitalizer, Tara is an extract from the fruits pods of the related C. spinosa. The tannin concentration is high in the pods; a typical analysis is:

• gallotannin 53.1%
• gallic acid 9.5%
• ellagitannin 6.9%

Other major sources of tannins are

• chestnut
• mimosa
• quebracho
• valonea
• myrobalans (fruits and twigs).
• tea
• rhubarb root
• geranium
• sanguisorba
• Polygonum bistorta
• Polygonum multiflorum

Many herbs contain tannins in nature, but have only a small or insignificant influence on therapeutic activity due to the type or degree of tannin in the herb. A Chinese-Tibetan herb recently popularized as an "adaptogen," rhodiola, is high in tannins (about 16-18% of the root, but as much as 40% of the hot water extract). In Ayurvedic medicine, the tannin-rich myrobalans fruits, such as amla (Emblica officinalis), are used like the Polygonum multiflorum (heshouwu) as anti-aging remedies.

Pharmacology - Tannins comprise a large group of natural products widely distributed in the plant kingdom. They have a great structural diversity, but are usually divided into two basic groups:

• Hydrolyzable tannins - are readily degraded into smaller molecules. Hydrolyzable tannins are present in many different plant species but are found in particularly high concentrations in nutgalls growing on Rhus semialata (and Korean gallotannins) and Quercus infectoria (Turkish and gallotannins), the seedpods of Caesalpinia spinosa (Tara tannins), and the fruits of Terminalia chebula. The hydrolyzable tannins react with proteins to produce the typical tanning effect; medicinally, this is important for treatment of inflamed or ulcerated tissues. They also contribute most of the astringent quality that is noted when drinking tannin-containing beverages. Hydrolyzable tannins include the commonly-occurring gallic acid and the ellagic acid.
• Condensed tannins - also known as proanthocyanidins, are much more resistant to decomposition and merely yield polymers or precipitates when acidified. The basic monomer of condensed tannins is epicatechin and catechin (identical except for orientation of the molecules, see below); these are then extended by the successive addition of similar phenol units to produce polymers (polyphenols). Traditionally, important commercial sources of condensed tannins are the heartwood of Schinopsis spp. (quebracho tannins), the bark and/or heartwood of Acacia catechu (catechu tannins) and Acacia mollisima (mimosa tannins), and the bark of Rhizophora (mangrove) and Eucalyptus species. The application of proanthocyanidins as health protective antioxidants was popularized through extracts of pine bark (particularly the branded product Pycnogenol) and grape seeds, which can be used interchangeably. In addition, proanthocyanidins were recognized as beneficial for vision, and are active components of bilberry extract sold for this purpose.

Both types of tannin have been used to treat diseases in traditional medicine, but the hydrolyzable tannins have long been considered official medicinal agents in Europe and North America. They are specifically referred to as tannic acid and recommended for treatment of inflammation and ulceration, including topical application for skin diseases and internal use for intestinal ulceration and diarrhea. Now, the condensed tannins also have important medicinal roles, such as stable and potent antioxidants. In China, tannin-containing substances, such as galls, pomegranate rinds, and terminalia fruits, are used in several medicinal preparations.

Medical Use of Tannin containing Herbs - Herbs that have tannins as their main component are astringent in nature and most such medicinals are listed in the Materia Medica category of astringents. The most common applications are in treating:

• Intestinal disorders, such as diarrhea and dysentery, intestinal parasites, rectal prolapse, hemorrhoids;
• Bleeding, including functional bleeding, hematochezia (blood in the stool), bleeding hemorrhoids, and topically for bleeding wounds and ulcerations; and
• Excessive discharge, such as enuresis and frequent urination; leucorrhea; hyperhidrosis (excessive sweating) and night sweating; involuntary seminal emission.

Herbs of medicine with tannins as a major component and their uses; these are listed in the Materia Medica category of astringents (except catechu is listed with topical therapies):

Note - Catechu (also known as Cutch, or Cashoo) is an extract of any of several species of Acacia - but especially Acacia catechu - produced by boiling the wood in water and evaporating the resulting brew. Catechu (called katha in Hindi) is an astringent and has been used since ancient times in Ayurvedic medicine as well as in breath-freshening spice mixtures. It has recently also been utilized by Blavod Drinks Ltd to dye their vodka black. Also called cutch, it is a brown dye used for tanning and dyeing and for preserving fishnets and sails. White cutch, also known as gambier, gambeer, or gambir, has the same uses.

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