Common name: Karaya gum

Karaya Gum or Kulu is a gum-yielding tree originating from India, where it occurs on dry, rocky hills and in the dry deciduous forests in the north and centre of the subcontinent.

It is a medium-sized deciduous tree, typically 9 to 15 m (30 to 50 ft) tall, with a short, crooked trunk supporting a much-branched, rounded crown of twisted branches. The bark peels off in transparent, papery flakes, exposing smooth, creamy-white underbark that contrasts strongly with the usually darker surroundings.

The leaves are large, 23 to 30 cm (9 to 12) long and just as wide, with five pointed lobes resembling a maple leaf. They are clustered at the ends of the branches and, with the onset of the dry season, change colour from green to yellow, then fall to the ground, leaving the branches bare and exposed.

Flowering follows leaf fall in the dry season, with flower clusters arising at the ends of the branches bearing small yellowish flowers. Fertilised flowers develop into softly hairy, star-shaped seedpods. When young, they are yellow-green, becoming orange or bright red when mature, and contain small black oval seeds.

Use

The bark, when wounded, yields 'Gum karaya' or 'Indian tragacanth', a commercial gum almost as important as Gum Arabic (from Senegalia senegal). When placed in water, it is an insoluble gum that swells to a jelly-like mass, transforming into a thick, translucent paste with enough water. In India, it is employed mainly as a gelling agent in confectionery. Outside India, it is used more as a substitute for gum arabic and Gum tragacanth, a gum obtained from several species of Astragalus, a tree species originating in Asia Minor, or modern-day Iran, Syria, and Turkey. 

Gum karaya is used as a thickening agent, gelling agent, stabiliser, and emulsifier in a wide range of food, pharmaceutical, and cosmetic products.

In food, it is used in bottled sauces and salad dressings, dairy products such as whipped cream and cheese spreads, and sausage meats to improve adhesion between the different ingredients. Its moisture retention and absorption properties also slow staling in baked goods and retards ice crystal formation in frozen desserts such as ice cream, mousse, and popsicles.

It is used in hair sprays, beauty masks, shaving creams, toothpaste and cosmetics. It is also a common ingredient in denture adhesive powders. 

Gum karaya is also used as a dye thickener in the textile industry and as a deflocculant and binder in paper manufacturing.

Gum collectors in India drill one or two holes in the tree trunk, then later collect the exudate, which can weigh up to 1 kg (2.2 lbs). A single tree may yield 2 to 5 kgs (4.4 to 11 lbs) of gum in a season, though it is not tapped every season so that it can have a rest period to recover. The highest yields and best-quality gum are obtained toward the end of the dry season, just before the monsoon season in its native region. 

The wood is medium-weight, averaging about 670 kg per cubic meter (42 lbs per cubic ft), and resists insect attack. However, it is usually harvested only for firewood and charcoal. 

Health use

Gum karaya has laxative action because it absorbs large amounts of water and expands up to 100 times its initial volume.

Climate

Grows naturally in sub-humid to moderately humid subtropical and tropical climates with a long dry season, generally areas with annual lows of 17 to 21°C, annual highs of 24 to 36°C, annual rainfall of 300 to 1900 mm and a dry season of 6 to 10 months. However, the trees that yield the most gum are found in areas with annual rainfall of 700 to 1300 mm. 

Growing

New plants are usually started from seed, which germinates readily without pre-treatment. They germinate within around three weeks. 

It performs best on free-draining loam and sandy soils that are moderately acidic to slightly alkaline, generally with a pH of 5.5 to 7.5, and on sites with full to partial sun exposure. The tree has poor tolerance for slow-draining or saturated soils and shade.

Problem features

There appears to be no record of it as a weed or invasive species.

Books

• Brady, G. S. & Clauser, H. R & Vaccari, J. A. 2002, Materials handbook : an encyclopedia for managers, technical professionals, purchasing and production managers, technicians and supervisors, 15th ed., McGraw-Hill, New York

• Champion, H. G. & Seth, S. K. 1968, A revised survey of the forest types of India, Natraj Publishers, Dehradun, India

• Coppen, J. J. W. 1995, Gums, resins and latexes of plant origin, Food and Agriculture Organization of the United Nations (FAO), Rome

• Groom, N. 1997, The new perfume handbook, 2nd ed., Blackie Academic & Professional, London

• Howes, F. N. 1949, Vegetable gums and resins, Chronica Botanica Company, Waltham, Massachusetts

• Imeson, A. 2010, Food stabilisers, thickeners and gelling agents, Wiley-Blackwell Publishing, Chichester, United Kingdom

• Khan, I. A. & Abourashed, E. A. 2010, Leung's encyclopedia of common natural ingredients : used in food, drugs and cosmetics, 3rd edition, Wiley Publishing, Hoboken, New Jersey

• Leakey, R. R. B et al. 1996, Domestication and commercialization of non-timber forest products in agroforestry systems : proceedings of an international conference held in Nairobi, Kenya, Food and Agriculture Organization of the United Nations (FAO) Press, Rome.

• Luna, R. K 1996, Plantation trees, International Book Distributors, Dehradun, Uttarakhand

• Parrotta, J. A. 2001, Healing plants of peninsular India, CABI Publishing, Wallingford, Oxfordshire

• Roecklein, J. C & Leung, P.S. 1987, A Profile of economic plants, Transaction Books, New Brunswick, New Jersey

• Troup, R.S. & Joshi, H. B. 1975 to 1981, Silviculture of Indian Trees (3 volumes), Government of India Publications, New Delhi

• Winter, R. 2009, A consumer's dictionary of cosmetic ingredients : complete information about the harmful and desirable ingredients found in cosmetics and cosmeceuticals, 7th ed, Three Rivers Press, New York