Most natural gums are extracted from or tree sap or seed coatings, while some others are produced from seaweed or bacterial fermentation (see table below). Tree gums appear as sticky exudations on the trunks and branches of many species of trees or shrubs belonging to the family Fabaceae (Leguminosae) of the pea order Fabales, which are spread across the arid regions of Africa, the Middle East, India, the Americas and Australia. The trees naturally exude the gum in response to damage to their internal tissues, through a process known as gummosis which is believed to guard against bacterial infection, fungus and insect attack. Gum flow can be stimulated by deliberately wounding the tree by making an incision in the bark and then tapping the exudate.
Natural gums are often sold in the form of small, dried lumps, which are usually transparent and light yellow. They are polysaccharides of natural origin and can be classified as either ionic polymers (polyelectrolytes) or uncharged polymers (see table below). Chemically, gums consist essentially of polymeric carbohydrates which hydrolyse easily to form sugars, notably hexose, pentose and arabinose, saccharides, some water, natural colouring matter of a pale tint and small quantities of impurities. Alkali metal salts of acids combined with sugars form part of the total, while nitrogen is often present but is not an essential constituent.
The main factor that distinguishes gums from resins and oleo-resins, is that gums are soluble in water. Gums are uncrystallisable hydrophylic colloids that can be divided into two groups. The first group (e.g. Gum Arabic) dissolve readily in water to form a more or less clear solution. The second group (e.g. Tragacanth) absorb large amounts of water and swell at first to form thick gel-like mucilages before subsequently dissolving as more water is added to yield an opaque viscous sol (colloidal solution). It is the ability of gums to form semi-solid and liquid materials with colloidal properties that makes them so useful across many diverse industries. When added to an aqueous solution, they are capable of causing a large increase in viscosity, even when added in small concentrations.
Gums are insoluble in alcohol, ether and other organic solvents and do not melt upon heating but ultimately decompose.
Natural gums are widely used across the food, confectionery, pharmaceutical, personal care, paint and printing industries for a variety of applications. They are often dissolved in water-based solutions and function as binding agents, adhesives and encapsulating agents once the water evaporates. They are also used as sizing, a protective filler or glaze that changes the absorption and wear characteristics of textiles and paper.
Natural gums are commonly used as food additives, with many having been allocated E numbers by the European Commission (see table below). They mainly function as emulsifiers, stabilisers, thickeners and gelling agents, but are also used as clarifying agents, flocculants, swelling agents, foam stabilisers and crystal inhibitors.
Listed below are some of the main natural gums, including their source and type:-
Ionic Polymers (Polyelectrolytes)
|From Seaweeds||Agar (E406) from red algae of the genara Gelidium and Gracilaria.|
|Alginic acid (E400), from the cell walls of brown algae.|
|Carrageenan (E407), from red edible seaweeds.|
|Sodium alginate (E401), from the cell walls of brown algae.|
|From Trees and Seeds||Gum Arabic/Acacia (E414), from the sap of Acacia trees.||Beta-glucan, from oat or barley bran.|
|Ghatti (E419), from the sap of Anogeissus trees.||Chicle, from the Chicle tree.|
|Tragacanth (E413), from the sap of Astragalus shrubs.||Damar, from the sap of Dipterocarpaceae trees.|
|Karaya (E416), from the sap of Sterculia trees.||Konjac (E425), from the Konjac plant.|
|Guar (E412), from Guar beans.|
|Locust Bean/Carob gum (E410), from the seeds of the Carob tree.|
|Mastic, from the Mastic tree.|
|Psyllium seed husks, from the Plantago plant.|
|Spruce gum, from spruce trees.|
|Tara gum (E417), from the seeds of the Tara tree.|
|From Bacterial Fermentation||Gellan gum (E418), from bacterium Sphingomonas elodea.||Xanthan (E415), from bacterium Xanthomonas campestris.|