Natural plant resins and gums

Introduction

Resins and gums occupy a prime place among Non-wood Forest Produce (NWFP), and are known to mankind since time immemorial. These are perhaps the most widely used and traded NWFP's other than items consumed directly as food, fodder and medicine. Use of gums and resins for domestic consumption and sale to earn some cash is very common among the forest dwelling communities, particularly tribals in India. Thousands of forest dwellers particularly in the central and western Indian states depend on gums and resins as a viable source of income.

Resins and gums are metabolic by-products of plant tissues either in normal course or often as a result of disease or injury to the bark or wood of certain plants. There are a large number of trees in India which exude gums and resins. Some of these are of local or limited interest, while a few are used extensively all over India and also entered the export trade of the country. The total export of natural resins, gums and gum-resins during the year 2013-14 was 621246.6 tons valued Rs 12722.8 crores and total import was 37981.6 tons valued Rs 799.9 crores.

The gums and gum-resins of commercial importance collected from the forest are gum karaya, gum ghatti, salai gum, guggul, and gums from various species of Acacia, including Indian gum arabic from Acacia nilotica and true gum arabic from A. senegal. The importance of commercial resins are obtained from Pinaceae (rosin, amber), Leguminosae (copal) and Dipterocarpaceae (dammar) families.

The uses of natural gums and resins in food, medicines and in varnishes or as protective coatings go back to very early times. The present day uses of natural gums and resins are numerous and they are employed by a large number of manufacturing industries including food and pharmaceutical industries. Some of the plant based gums and resins of commercial importance are presented here.

Natural Resins

Resin secretion occurs in special cavities or in many plant species. They are formed in the specialized structures called passages ducts. Resins exude or ooze out from the bark of the trees and tend to harden on exposure to air. With the exception of lac, which is produced by the lac insect (Kerria lacca), all other natural resins are of plant origin. Natural resins of particular importance to the furniture coatings are rosin, damar, copal, sandarac, amber and manila.

The principal characteristics of resins are:

• They are insoluble in water.
• They are soluble in ordinary solvents like alcohol, ether and turpentine.
• They are brittle, amorphous and are transparent or semi-transparent.
• They have a characteristics luster, are ordinarily fusible and when ignited,resins burn with a smoky flame.

Natural Gums

Gums are a group of plant products, formed primarily due to the disintegration of plant cellulose. This process is known as gummosis.Gums are produced by members of a large number of families but exploitation is restricted to of commercial a few tree species Leguminosae, Sterculiaceae and Combretaceae families. The important gum yielding trees are Acacia nilotica (babul), A catechu (khair), Steruculia urens (kullu), Anogeissus latifolia (dhawra), Butea monosperma (palas), Bauhinia retusa (semal), Lannea coromandelica (lendia) and Azadirachta indica (neem). Gums is also extracted from seeds of certain plants like guar, tamarind, Cassia tora etc. Guar gum is the prominent seed based natural gum.

The principal characteristics of gums are:

• They consist of polysaccharides or their derivatives.
• They are soluble in water or at least become soft and swollen when mixed with water. However they are insoluble in alcohol and other organic solvents.
• They decompose completely on heating without melting and tend to become charred
• Most gums emanate from plants in a liquid form. They dry up into translucent,amorphous, tear-shaped bodies or flakes on contact with air.

Gum-resins

Gum-resins are a mixture of both gums and resins and possess the properties of both the groups. They contain traces of essential oils.These are usually derived from the plant growing in dry and arid regions. Some of the commonly used gum-resins ale asafoetida, myrrh, salai, guggul etc.

Source: Indian Institute of Natural Resins & Gums