**Abstract**

With the advent of science and technology, agro-industrial wastes are converted into various value-added products to meet the demands of increasing population. In recent years, natural polymers have evoked tremendous interest due to easy conversion into value-added products. Apart from various natural polymers, pectin occupied a prominent place due to diverse pharmaceutical and therapeutic applications. Excess utilisation of pectin, the gap between production and demand is widening. To fulfil this gap various techniques are adopted for obtaining high yield pectin from various agro-industrial wastes. This chapter will be focusing on extraction and purification of pectin from various agro-industrial wastes, considered as main environmental pollutants.

**Keywords:** agro-industrial, waste, pectin, pharmaceutical, therapeutic

### **1. Introduction**

Pectins are complex branched polysaccharides present in the primary cell wall of plants [1]. It is a highly valued food ingredient commonly used as a gelling agent and stabilizer [2]. It is usually extracted by chemical or enzymatic methods from fruits [3]. Pectin is considered as the most complex macromolecule in nature, since it can be composed of up to 17 different monosaccharides containing more than 20 different linkages [4].

Pectins are enriched with repeated units of methyl ester galacturonic acid [4]. They form chemically stable and physically strong skeletal tissues of plants when combined with proteins and other polysaccharides [5]. They are usually produced in the initial stages of primary cell wall growth and make one third of the cell wall in both monocots and dicots [6]. Pectin is significantly reduced or absent in non-extendable secondary cell walls and is the only major class of plant polysaccharide largely limited to primary cell walls [7]. Pectin imparts strength and flexibility to the cell wall, apart from number of fundamental biological functions such as signalling, cell proliferation, differentiation, cell adhesion and maintaining turgor pressure of cell [8]. Pectins are involved in regulating mobility of water and plant fluids through the rapidly growing parts [6]. It also influences the texture of fruit and vegetables [9]. Apple pomace

and orange peel are the two major sources of commercial pectin due to the poor gelling behaviour of pectin from other sources [6].

Pectin is one of the most important polysaccharides due to its increasing demand in the global market, reaching a total production capacity of around 45–50 Million tonnes per annum. While the demand in 2011 was approximately 140–160 Million tonnes per annum, earning the interest of industry in this complex polysaccharide processing [10]. Pectins have received considerable attention as a high fibre diet that benefits health by reducing cholesterol and, serum glucose levels and acting as anticancer agents [11]. Pectins have shown promising results as drug carriers for oral drug delivery and are widely used for various bio-medical applications [5]. In addition, pectin has been described as an emerging prebiotic with the ability to modulate colon microbiota [12]. Considering above properties and applications, pectin has gained immense priority in the global biopolymer market with great potential and opportunities for future developments.

#### **2. Structure and properties of pectin**

One of the most abundant macromolecules present in the primary cell wall of the plants is pectin; their presence is detected in the matrix as well as in the middle lamellae [7]. Pectin is highly rich with galacturonic acid (GalA), that forms the backbone of three more domains found along with pectin that are homogalacturonan (HGA), rhamnogalacturonan-I (RG-I) and rhamnogalacturonan-II (RG-II) [13]. About 70% of pectin is mainly composed of galacturonic acid (GA) [14]. Pectin is made of three polysaccharides that are covalently linked together, thus forming pectin networks in the cell wall matrix and the middle lamellae [15, 16].

Homogalacturonan (HG) takes up about 60–65% of the total pectin [3, 17], with a backbone of alpha-1,4-linked GalA residues, these GalA residues are methyl esterified which has an important role in the physical properties of pectin [4]. The presence of HG is seen to be present in approximately 100 GalA residues, but there are cases when its detected interspersed within other pectin polysaccharide [14]. On the other hand rhamnogalacturonan-I (RG-I) backbone which contributes 20–35% of pectin is composed of repeated and alternating groups of l-rhamnosyl and d-galacturonosyl residues [18]. There can be as many repeats as 300 of this disaccharide in case of sycamore cells, which are cultured in suspension [3, 16, 19]. The rhamnosyl residues have side chains of sugars which are mainly consisting of either galactosyl or arabinosyl residues [5]. The GalA residue of RGI unlike HGA are mostly not methyl esterified [20].

Rhamnogalacturonan-II (RG-II) is one of the highly conserved and complex structure which consist of distinct regions within HG, which makes up about 10% of the pectin [3], they have side chains of four different types with a particular sugar residue like aceric acid, apiose-3-deoxy-lyxo-2-heptulosaric acid, and 3-deoxy-manno-2-octulosonic acid. The HG residues along with nine of the GalA residues are attached to these side chains [3, 5]. There are other substituted HG residues that make up pectin such as xylogalacturonan and apiogalacturonan whose expression is restriction. Even a minor mutation in R-II structure can lead to defects in the plant growth like dwarfism, thus suggesting its importance for normal growth of plant [3]. RG-I being highly branched in nature thus, called as the hairy region of pectin on the other hand HGA domain are known as the smooth region [7]. It is generally believed and noticed that there is covalent linkage within the pectin polysaccharides and pectin degrading enzymes are needed to separate and isolate HG, RG-I and RG-II from each other [21, 22]. Due to their similarity in

**49**

*Extraction and Purification of Pectin from Agro-Industrial Wastes*

group that is mainly responsible for its precipitation [24].

polymer chains stabilizes the pectin polymer [9].

present in the peel of fruits [26].

**4. Extraction and purification of pectin from agrowaste**

HG and RG-II backbone structure composing of 1-4-linked alpha-D-GalA residues, they are likely to be linked covalently but there are no reports of RG-I to be cova-

Pectin precipitates as a solid gel on treating with a dehydrating agent like alcohol. They are extremely sensitive to dehydration and get effected by any other hydrophilic colloids as well, thus they are known to be insoluble in most of the bio-colloids. The negative charge of pectin depends on the number of free carboxyl

Based on solubility pectins are of two types i.e., water soluble and water insoluble. Factors affecting the solubility of pectin are pH, temperature, nature of the solute and concentration of the solute [6, 13]. Pectin attains stability at a pH of 4 [17]. The solubility of pectin also depends on its composition like monovalent cation of pectin are soluble in water whereas di or trivalent are insoluble in water.

One of the most interesting properties of pectin is its ability to form gel in the presence of either acid or calcium or sugar, this enables them to be used in many food industries [15]. Hydrogen bonding and hydrophobic interactions between

Pectin is a high molecular weight polysaccharide that is present in almost all plants and help in maintaining the integrity of cell structure. Pectin is used in food industries to increase the viscosity of food products such as beverages, jams and jellies. It also has implications in pharmaceutical industry, especially in drug formulations, as an excipient due to its characteristics in release kinetics. Due to increased demand for pectin in food, pharmaceutical and therapeutic applications, thus, require efficient extraction processes. In order to increase the yield of pectin, various extraction methods have been adapted to obtain insoluble pectin present in the middle lamellae of plant cells, one of them being heating in acidic medium that makes insoluble pectin as soluble. Ripening of fruits also converts insoluble pectin into soluble pectin. Pectin can be extracted from various kinds of fruits, but the most commercial form of pectin is extracted from the peels of citrus fruits by alcohol precipitation [9, 25]. Citrus fruits contain 0.5–3.5% pectin which is largely

Pectin has been isolated from various plants such as apple [27], citrus peel, carrots [28], sugar beet pulp [29, 30], sunflower heads [31], papaya [32] and oranges [33]. The most commonly used method for extracting pectin from plant tissue is by heating the plant sample in acidified water. The addition of extra chelating agents such as EDTA to the extraction mixture helps in easy release of pectin from cell wall. Care should be taken not to perform a long period of direct heating as it may lead to the thermal

*DOI: http://dx.doi.org/10.5772/intechopen.85585*

lently linked with HG [23].

**3. Properties of pectin**

**3.1 Colloidal**

**3.2 Solubility**

**3.3 Gelation**

HG and RG-II backbone structure composing of 1-4-linked alpha-D-GalA residues, they are likely to be linked covalently but there are no reports of RG-I to be covalently linked with HG [23].
