CHAPTER TWO
LITERATURE REVIEW
2.1 Arabic Gum
Gum Arabic is a natural plant polysaccharide, a dried exudate of acacia trees (family: Leguminosae). Gum Arabic is the oldest plant polysaccharide in use by man and its use begun around 5000 years ago. Gum Arabic is obtained from acacia trees around the world (around 900 species) but the largest production come from regions of Africa like Sudan, Nigeria, Senegal, and Mauritania [79]
In ancient times, in Egypt use of GA was reported as a mineral pigment adhesive in paint and for embalming mummies (Whistler and BeMiller, 1993). Some species of the Acacia genus are the source of GA. Due to its natural origin and safety record, it is recognized as the most crucial exudate gum. It finds application in food, pharmaceuticals, cosmetics, textile, paper, ink, adhesive, paint and printing. It is mainly produced in sub-Saharan Africa and small quantities in Arabian Peninsula and South Asia. GA is primarily consumed in developing and developed countries. The annual average export of crude and semi-processed gum was about 35,000 tons in 1992–94, which increased to 102,000 tons during 2014–16. During this period, processed gum exports increased from 17,000 tons to 53,000 tons. The value of GA export during 2014–16 was an average of $337 million per year, in which the contribution of crude gum and semi-processed gums were 44 & 56%, respectively (Jales, 2018).
Acacia senegal is a drought-resistant tree found naturally in arid, subtropical and semi-arid climatic zones (Omondi et al., 2010). It is a deciduous, small, spiny shrub and usually branched from the ground of 2–6 or even 12 m high (Fig. 1a) (Duke, 2012). Branches bifurcate repeatedly, and when fully grown, the tree forms a rounded, flat-topped crown. The trunk of the tree has a diameter of about 30 cm and is found covered with greyish-white bark (Gardens, 2016). The tree has alternate pinnately compound leaves, green-grey and 3.5–8 cm long (Fig. 1b). Two glands are present between the uppermost and lowermost pinnate. Leaflets are small, linear to elliptic-oblong, and their tip is either blunt or somewhat pointed. The flowers are found on cylindrical spikes and are yellowish-white in colour, possessing fragrance (Fig. 1c). When matured, the pods are straight, thin, flat, oblong and green (Fig. 1d). The tree is armed with three powerful hooked thorns just below the nodes, one pointing forward and the other backwards (Fig. 1d).
Seeds are dark-brown in colour and appear smooth, flat and shiny (Fig. 1e) (Duke, 2012). The flowers in this tree often appear before the first rain; however, sometimes, it also appears towards the end of the rainy season (July - September). Apart from taking gum production from the Acacia senegal tree (Fig. 1f), it is also used in developing green walls to confine the desertification. Acacia senegal leaves incorporated in soil improve its fertility, and is a leguminous tree, and it helps in nitrogen fixation in the soil. Its wood is used for firewood, construction and posts for fencing (Odee et al., 2012).
The Acacia trees play an essential environmental and sociological role in Savanna region countries in Africa(Karamalla et al., 1998; Mukhtar, 2001). Acacia senegal trees grow naturally or are planted in these regions for gum production. Sudan is the world's largest and best-quality GA producer (Balla, 2006).
Acacia senegal is found abundantly in sub-Sahara African countries, i.e. Mauritania, Mali and Senegal in the west; Burkina Faso, Niger, Benin, Nigeria, Chad and Cameroon in the northern central region; Sudan, Somalia, Eritrea and Ethiopia in the East; and Angola, Mozambique, Zimbabwe, Botswana, Namibia, and South Africa in the West. Apart from Africa, Acacia senegal is also found in Pakistan (Sindh and Baluchistan), Oman and India (Rajasthan, Haryana, Gujrat, MP, UP and Punjab) (Islam et al., 1997).
Acacia senegal trees are also found in large numbers, even in rocky land forms spread over Arid Western Rajasthan, accounting for 23,520 sq. km. Bringing untapped trees in these areas for GA production and adopting an improved gum tapping method may substantially increase GA production in India. Further, there are scopes of increasing GA production in Africa by bringing more area under Acacia senegal plantation and planting these trees on field boundaries in potential GA producing countries, i.e. Sudan, Nigeria, Niger, Senegal and Mali (Muhammad et al., 2020).
Acacia senegal tree has a typical thorn (Fig. 1d) which gets entangled when animals or human beings come in contact with it, and it becomes challenging to disengage the thorn quickly. These characteristics of Acacia senegal tree thorn make the tree ideal for bio-fencing. These trees at the field boundaries and some other small shrubs like C. carandas planted between two Acacia senegal trees can work as bio-fence for the agricultural field.
Gum arabic also known as acacia gum is highly branched water-soluble polysaccharide, mainly obtained from Acacia senegal and Acacia seyal trees. Structurally, it’s composed of galactopyranose, l-arabinose, l-rhamnose, d-glucuronic acid, and some protein as well.
GA (also known as acacia gum, chaar gund, char goond, or meska) is sourced from Acacia Senegal and Acacia Seyal.
2.1.1 Properties of Arabic Gum
Gum Arabic is unique among the natural hydrocolloids because of its extremely high solubility
in water. Gum Arabic is insoluble in oil and in most organic solvents. It is soluble in aqueous ethanol up to a limit of about 60% ethanol. Limited solubility can also be obtained with
glycerol and ethylene glycol. Whereas most gums form highly viscous solutions at low
concentrations of about 1-5%. High viscosities are not obtained with Gum Arabic until
concentrations of about 40-50% are obtained. This ability to form highly concentrated
solution is responsible for the excellent stabilizing and emulsifying properties of Gum Arabic
when incorporated with large amounts of insoluble matters. The viscosity of Gum Arabic
solutions will depend upon the type and variety of the Gum Arabic used. At concentration up
to 40%, Gum Arabic solutions exhibit typical Newtonian behavior. Above 40%, solution takes
up pseudoplatic characteristics as denoted by a decrease in viscosity with increasing shearing
stress, Benecke, (2009).
In Nigeria, Gum Arabic is classified into 3 grades namely.
i. Acacia Senegal (grade 1)
ii. Acacia Seyel (grade 2)
iii. Combretum and other source, Abubakar (2004).
Gum Arabic is mainly produced from two Acacias that are found to a varying intensity in the
belt of sub-Saharan Africa. The Acacias are; Acacia Senegal that produces hard gum and
Acacia Seyel that produces friable gum, Macrac and Miller (2002).The Gum Arabic of
commercial is water soluble exudates. The major source (95%) is Acacia Senegal while the
remaining 5% is from Acacia Seyel, which are sold as an entirely separate product. Both
trees species grow in various communities in the drier parts of Africa and Asia, Seifel (1969).
Friable gum is considered to have a relatively low quality and may be used for a price
advantage or when supplies of hard gum are low, Macrase and Miller (2002).
Gum Arabic is a complex, slightly acidic polysaccharide. The precise chemical and molecular
structure differs according to the botanical origin of the gum. As a result, the functional
properties and uses to which Gum Arabic can be put (and its commercial values) are very
dependent on its origin.
Arabic gum, also known as acacia gum, is a natural exudate derived from the sap of certain species of Acacia trees. It has been used for various purposes throughout history, owing to its unique properties and versatile applications.
2.1.1.1 Chemical Composition:
Arabic gum primarily consists of complex polysaccharides, with arabinose, galactose, rhamnose, and glucuronic acid as the main sugar constituents. It also contains glycoproteins and traces of minerals.
2.1.1.2 Physical Properties
Gum arabic, also known as acacia gum, has a wide range of applications across various industries. Here are some of its primary applications:
2.1.2.1 Food Industry
1. Emulsifier and Stabilizer: Used in beverages, confectionery, and processed foods.
2. Coating Agent: Provides a glossy finish on candies and nuts.
3. Texture Modifier: Improves the texture of baked goods and dairy products.
2.1.2.2 Pharmaceuticals
Binder: Used in tablet formulations to impart cohesion.
Suspension Agent: Helps to suspend insoluble drugs in liquid preparations.
Film Coating: Used for taste masking and controlled release of drugs.
2.1.2.3 Industrial Applications
1. Adhesive: Used in industries like paper and printing for its adhesive properties.
2. Textile Printing: Used as a thickener in dyeing processes.
2.1.2.4 Health and Wellness:
Dietary Fiber: Used as a dietary supplement due to its prebiotic properties.
2.1.2.5 Safety and Regulatory Aspects:
Arabic gum is generally recognized as safe (GRAS) by regulatory authorities like the FDA in the United States.
2.1.3 Challenges and Future Directions
Despite its widespread use, there may be issues related to sourcing, quality control, and sustainability of production.
In conclusion, Arabic gum's unique properties, including its solubility, emulsification, and film-forming abilities, make it a valuable ingredient in a wide range of industries. Ongoing research aims to further explore its potential applications and address challenges associated with its production and use.
REFRENCES
Pragnesh N. Dave, Ankur Gor, in Handbook of Nanomaterials for Industrial Applications, 2018. Showkat Ali Ganie, ... Qing Li, in Advanced Green Materials, 2021.
Vinod V.T. Padil, ... Miroslav Černík, in Comprehensive Analytical Chemistry, 2021.
Abubakar A. (2004) Report on Survey of Selected Agricultural Raw Materials in Nigeria (Gum Arabic). Submitted to Raw Materials Research and Development Council Abuja.
Grieve, M. (Mrs), (2009) A modern Herbal (Gum Acacia) Botanical Com. Macrae, J. & Miller, G. (2002) “The prospect and Constraints of Development of Gum Arabic in sub-Sahara Africa” Washington, D. C, World Ba