**3. Conventional sources of pectin and their applications**

Commercial pectin is generally obtained from citrus peels (25% dry matter) and apple pomace (15–18% dry matter), their processing subproducts, and sugar beet pulp (25% dry matter) [18]. The most significant part of commercial pectins includes 85.5% from citrus peels, 14% from apple pomace, and ~ 0.5% from sugar beet pulp [19]. Industrial processes for the extraction of pectin are based on the thermal hydrolysis of the citric peels (mainly from orange, lemon, and lime), apple pomace, and sugar beet pulp by using hot mineral acids like HCl, H2SO4, or HNO3 (~pH 1.5) at ~85°C [20], where the control of the extraction conditions is of great relevance for minimizing the de-esterification and depolymerization of the polysaccharide and improving the functional properties of pectins as gelling, fiber enrichment, stabilizer, texture, and rheology control agent [21]. Notably, these pectin extraction processes generate large amounts of acidic industrial wastes and high energy consumption [22]. Hence, recent investigations have explored the use of more green technologies to overcome these environmental issues and enhance yield extraction [23]. **Table 1** shows some physicochemical properties of pectins obtained from conventional sources using different extraction procedures.


*HHP: High hydrostatic pressure; MW: Molecular weight; ηint: Intrinsic viscosity; USE: Ultrasound-assisted extraction; WHC: Water holding capacity; OHC: Oil holding capacity.\* Depending on the variety of pomace.*

#### **Table 1.**

*Physicochemical properties of some pectin extracted from conventional sources.*

Pectin is widely used in the food industry as an excellent thickener agent for producing jellies and jams, a pH stabilizer in dairy products and low-calorie products, and an emulsifier in pharmaceutics for the design of drugs to treat gastrointestinal disorders, blood cholesterol reduction, and cancer treatment as well as good former of edible films and coatings, foams, and paper substitutes [17, 24]. Because of the

*New Sources of Pectin: Extraction, Processing, and Industrial Applications DOI: http://dx.doi.org/10.5772/intechopen.109579*

**Figure 2.**

*Principal applications of commercial pectin in food, packaging, and pharmaceutical industries [17].*

functional properties of pectins, both LM and HM, many applications in food, industrial, and pharmaceutic sectors can be considered (**Figure 2**).

Most commercial pectins are facilitated to dissolution when a dextrose content is present. An additional pectin classification is based on its gelling capacity, which is relevant in product processing and preservation. Pectins are classified as rapid-set pectin, when gels are formed, preferably at high temperatures, generally used for jams because it reduces the possibility that the fruit rises to the surface before the pectin gel is set, and slow-set pectin, which is preferred in jellies because it allows handling the product before the gel setting without damaging the texture and firmness of the product [25].

Despite the presence of extensive contents of pectin polysaccharide in fruit subproducts, like citrus peels, apple pomace, or sugar beet pulp, it is not the most critical parameter to define a lucrative extraction and the best functional properties for this functional agent [17]; the exploration of novel sources of pectins is raising the attention of scientists and technologists.

### **4. Vegetable sources of pectin**

New sources of pectin that are receiving significant interest in the scientific field are those obtained from different kinds of vegetables, such as pumpkin, eggplant, chayote, and *Opuntia ficus* indica cladodes.

Several studies have been conducted on the extraction of pumpkin pectin using different extraction methods, such as the chemical acid treatment (0.1 M HCl) or enzymatic extraction, where the last has given much higher yields than the acid extraction [26]. Pumpkin pectin fraction **A** was obtained from raw pumpkin with an enzyme preparation of cellulase and α-amylase. Pumpkin pectin fraction **B** was

obtained by treating the solution of fraction **A** with pronase to reduce the protein content. The pumpkin pectin fractions **A** and **B** yielded 10.03 and 8.08 g/100 g, respectively.

The DE values of about 47% for pumpkin pectin fractions **A** and **B** were not significantly different, while the GalA contents represent 75.02 and 78.22 g/100 g, respectively. This finding indicated that both fractions are mainly composed of HG [27]. Small amounts (about 10 g/100 g) of six different neutral sugars were found in both pectin fractions, including rhamnose, arabinose, galactose, glucose, xylose, and mannose.

FT-IR and 1D NMR analyses revealed that the pumpkin pectin backbone is mainly composed of 1,4-D galacturonic acid, in which a considerable portion of galacturonic acid residues is present as methyl esters, and L-rhamnose is involved in the linear region of the backbone through α-1,2 linkages. The emulsifying capacity and stability of pumpkin pectin fraction **A** were 63.7 and 58.3%, respectively. At the same time, both properties were not detected in pumpkin pectin fraction **B**. Pectin fraction **A** exhibited emulsifying properties in the water–oil mixture, evidencing the presence of hydrophobic protein components in the pectin structure. In contrast, protein removal in fraction **B** resulted in a loss of emulsifying properties [26]. Therefore, pumpkin pectin could be used as an emulsifying agent in the preparation of oil-in-water emulsions for the beverage industry as long as residual hydrophobic protein components are not removed.

Eggplant fruit (*Solanum melongena* L.), a popular vegetable with an elongated oval shape and dark purple peels, grows worldwide, especially in tropical and subtropic regions. Under optimal extraction conditions by the ultrasound-assisted extraction method (UAE) (ultrasound power of 50 W, irradiation time of 30 min, and pH of 1.5), the pectin extracted from the peels of this vegetable (EPP) indicated that the EPP had a high GalA content (66.08 g/100 g) [28]. Considering the Food and Agriculture Organization (FAO) and European Union recommendations, the GalA content of pectin used as a food additive or pharmaceutical purpose should not be lower than 65 g/100 g pectin. This pectin had a high DE (61.22%) and was categorized as HM pectin (DE > 50%). EPP had a protein content of 2.53 g/100 g, which can be attributed to the difference in raw materials and extraction techniques. However, FAO suggests that the protein content of pectin should not be higher than 15.6 g/100 g [24]. In addition, EPP showed good values in functional features such as waterholding capacity (WHC) and oil-holding capacity (OHC). Under the optimal extraction conditions, EPP exhibited a WHC of 6.22 ± 0.21 g water per g EPP, while the OHC was 2.12 ± 0.15 g oil per g EPP. The emulsifying activity (EA) and emulsifying stability (ES) of EPP were evaluated, EA was about 56.16%, and the highest emulsion stability was 96.36 ± 0.80 at 4°C. EPP also exhibited antioxidant activity, determined by the DPPH radical scavenging method, reaching a highest antioxidant activity at a concentration of 50 mg/mL (94%), which was still lower than the antioxidant activity performed by the ascorbic acid, with an IC50 value of 1.39 mg/mL; this activity is due to the higher total phenolic content (TPC = 96.81 ± 2.18 mg GAEa/g pectin) associated to the EPP. The GalA content of the extracted pectin can be also effective in the antioxidant activity due to active portions in its structure [29].

Chayote is one of the most cultivated vegetables in the world. The major producing countries are Mexico, Brazil, and China [30]. The UAE method has been used to extract chayote pectin (PEUO) [31]. Using a liquid/solid ratio of 50 mL/g, a temperature of 70°C, and an ultrasonic time of 40 min as optimal extraction conditions. The yield was around 6.19%. Under these extraction conditions, PEUO exhibited a low DE (17.6%), indicating that the chayote pectin could be considered as LM pectin.

#### *New Sources of Pectin: Extraction, Processing, and Industrial Applications DOI: http://dx.doi.org/10.5772/intechopen.109579*

This property could be attributed to the harsh extraction conditions that would promote the de-esterification of polygalacturonic chains. The GalA content in PEUO accounted for 57.25%. To our knowledge, the ripeness, blanching, ultrasound, and other effects may influence the GalA content in the extracted pectin [31], besides the contribution to improve the depolymerization of polysaccharides, releasing the water-soluble pectin from the plant tissue [32]. The molecular weight in pectins significantly affects the emulsification, rheology, and their colloid stability. In this sense, the weight-average molecular weight and number-average molecular weight of PEUO were 2.47 × 106 g/mol and 1.29 × 106 g/mol, respectively, and the polydispersity index was 1.91. Polydispersity index higher than 1 suggests that PEUO extracted by UAE represents a heterogeneous natural polysaccharide with a broad range of polymer size distribution [31]. The monosaccharide composition of PEUO indicated the presence of five monosaccharides, where glucose (Glu) represents the most abundant monosaccharide (90.6%), followed by Gal (8%), D-Xyl (0.6%), Ara (0.6%), and Rha (0.2%). Besides, the content of Gal was significantly higher than that of Ara, indicating that the RG-I region may have been highly branched with galactan or arabinogalactan. Rheological properties of PEUO aqueous dispersions (<5%wt.) exhibited a non-Newtonian behavior [31]. Other functional properties like WHC and OHC for PEUO showed suitable values for both WHC (3.14 ± 0.42 g water/g PEUO) and OHC (3.73 ± 0.30 g oil/g PEUO). High WHC in PEUO makes it suitable as a food industry thickener. EA and ES were determined at 4°C and 25°C. The ES for PEUO emulsions were 88.36 ± 5.63% and 81.28 ± 4.82% after 1 day, and these values changed after 30 days to 85.33 ± 4.16% and 77.59 ± 5.19%, respectively. The lower temperature (4°C) was presumably more suitable for storing the PEUO emulsion. These results provide further evidence that chayote pectin may have great potential to be applied as an emulsifier and stabilizer in the food industry [31, 33]. Regarding the antioxidant activity of PEUO, it was higher when compared to pectin extracted from apples. Due to its techno-functional properties, PEUO may be used as a gelling agent and preservative in jam production or as a viscosity enhancer in beverages.

Another source of pectin that has received much attention is the *Opuntia ficus* indica (OFI) cladodes. This pectin has been extracted by acid water, ultrasound, and enzyme treatments [34, 35]. The pectin obtained by ultrasound under optimal conditions (sonication time of 70 min, temperature of 70°C, pH of 1.5, and water:solid ratio of 30 mL/g) reached an extraction yield of 18.14% ± 1.41%, with a GalA content of 68.87%. This pectin had a DE of 41.42%, classifying it as an LM pectin [36]. This DE value was higher than that achieved when the OFI pectin was extracted by the chemical process, which was 30.67% [37]. WHC in OFI pectin was 4.84 g water/g OFI pectin, ultrasound-induced cavitations in the pectin structure improving the water penetration and its absorption [38]. WHC for OFI pectin extracted by the chemical process was higher (5.64 g water/g OFI pectin) [34]. OHC for OFI pectin extracted with ultrasound was 1.01 g oil/g OFI pectin, slightly lower than pectin extracted by the chemical method (1.24 g oil/g OFI pectin) [34]. EA and ES were determined at two pectin concentrations (2 and 4% w/v). EA values were 19.23% and 26.92%, respectively, showing that the emulsion stability depends on the pectin concentration. OFI pectin at 4% maintained stability of more than 57% of the emulsion after 30 min of incubation at 80°C, unlike the 2% pectin solution, which could not retain more than 40% of the emulsion. This stability of the emulsions could be attributed to the rise of viscosities in the pectin solutions caused by the formation of a layer of pectin around each oil droplet, delaying the coalescence phenomenon [39, 40]. This stability was affected by the high pectin extraction temperature (> 45°C) [41]. ES in

OFI pectin extracted with acid water at 2% displayed higher values (90.45%) [34]. Differences in the ES are due to differences in the extraction methods, which affect the average molecular weight and the GalA content in the structure of pectin and therefore influencing the long-term stability in the emulsions [42]. When enzyme treatments were used for OFI pectin extraction, the optimal conditions were cellulase/xylanase at an LS ratio of 22 mL/g, cellulase/xylanase ratio of 2 U/U, and enzymes/matter ratio of 4 U/g, reaching an extraction yield of 17.91% [35], being more effective than the chemical treatment, which resulted in an extraction yield of 6.13 ± 0.60% [34]. Enzyme-assisted extraction of pectin depends on the choice of enzymatic activities based on the strength of pectin connection with cellulose and xylan and their abundance in the cell wall of the plant source [43].

For OFI pectin, the total sugar content was 89.94%, the main monosaccharide was GalA (66.66 ± 2.46%), with a DE of 35.04%, which was higher than that reported by Lira-Ortiz et al. [44] for pectin from prickly pear fruits (*Opuntia albicarpa*; DE 30.7%). OFI pectin had a WHC of 5.42 ± 0.16 g water /g OFI pectin, slightly lower than that for pectin extracted by the chemical process (5.64 g water/g OFI pectin) [34]. Various intrinsic factors, like the chemical structure of the biomaterial, and extrinsic factors, such as the pH, temperature, and ionic strength, can affect the WHC [45]. The OHC value of pectins was 1.23 ± 0.42 g oil/g OFI pectin. It was like the OHC of the OFI pectin extracted by the acid water method [34]. Thus, the oil retention power depends essentially on the hydrophilic nature and the overall charge density of the constituents [45]. EA values for OFI pectin emulsions at 2 and 4% were 26.9% and 30.77%, respectively. These values were lower than the ones found by Bayar et al. [34] for a 2% concentration of pectin extracted by the chemical process from the OFI cladodes (35%), proving that the extraction process influences the functional properties of pectin macromolecules [46]. The ES rates were 14.31% and 87.48% for 2% and 4% of pectin hydrocolloid in the emulsions, this long-term stability when emulsions were submitted to temperature treatment at 80°C is due to the high viscosity of pectin solution and by the formation of layers around the fat globules by the pectin [39].
