# Extraction, Characterization, and Applications of Pectins from Plant By-Products
## 3 Pectin Extraction Methods
### Traditional Methods for the Pectin Extraction  
In industry, pectin extraction is generally performed using strong acid solutions such as nitric, sulfuric, phosphoric, and hydrochloric acids, under heating [34]. Conventional pectin extraction takes several hours to obtain a good yield using boiling water [35; 36]. During the long heating process, the thermal degradation of pectins by beta-elimination and debranching leads to low-quality pectins. Therefore, pectin is extracted in acidic aqueous medium (pH 1.5-3) between 75 and 100 \({}^{\circ}\)C for 1-3 h with continuous stirring. In pectin extraction, the use of mineral acids has been related to environmental issues and increased costs. With regard to the emerging concept of \"green chemistry\" and \"green technology\", the focus is now shifting to organic acids (acetic and citric acids). Organic acids possess lower hydrolysis abilities compared to mineral ones [2]. Conventional extraction depends on several factors, such as temperature, pH, solvent properties, solid to solvent ratio, particle size, and diffusion rate [1]. After pretreatments of washing with water, blanching with hot water to inactivate enzymes, drying to remove water, and grinding to increase the exchange surface, pectin is extracted in an acidic aqueous medium and separated by alcohol precipitation from many other materials. The coagulate obtained is then filtered to clarify the extract, washed, dried under vacuum, and finally ground into a fine powder. Between the filtration and washing, the extract can undergo different steps. For example, the color of apple pectin can be removed by using activated carbon, and the residual starch can be degraded using amylase. Additionally, chemical, acid, and/or alkaline de-esterification can be used to obtain LM pectin. The extracted pectins generally have a DM between 55 and 75% and high molecular weights. The choice of solvent is based on several criteria, which are: dissolving of the specific components, high capacity for the solute separated into it, selectivity, stability, renewability, and low viscosity [37]. Chelating agents (CHAs), such as oxalate, have been used for pectin extraction. The efficiency of chelating agents for pectin extractions is impacted by the Ca\({}^{2+}\) content and the distribution of free acid groups in the HG chain [36]. CHAs solubilize high molecular weight pectins with a high DM [38]. Acid aqueous medium with low pH stimulates protopectin hydrolysis and solubility and promotes Ca\({}^{2+}\) and Mg\({}^{2+}\) removal, thus enabling higher isolated yields of HG-enriched pectin. Alkaline-extracted pectins have usually many RG-I oligomers branched with arabian and galactan side chains, low DM, and low yields [36]. Conventional pectin extraction using mineral acids has some important drawbacks, such as degradation of pectin, losses of some volatile compounds, increased costs for manufacturers, and environmental problems. Therefore, organic acids such as citric and acetic acids have attracted considerable interest [39]. Although strong mineral acids are cheaper and more effective than organic acids to extract pectin, The use of organic acid in the extraction of pectin leads to less hydrolysis and less depolymerization of the extracted pectin than the use of mineral acid [1]. Using citric acid with microwave heating provided higher DE values than using HCl with the same method [40]. This might have been due to the strong acid causing the demethylation and fragmentation of polygalacturonans [41]. Citric acid was reported to be a less pectin-degrading agent compared to HCl [2]. It is expected that the pectin extracted with organic acid as a solvent has a higher molecular weight compared to that of pectin extracted using mineral acid. The degree of esterification decreases with increasing heating time [42; 43]. Different extraction methods lead to the production of pectins with different DEs [41; 44; 45]. A low-viscosity solvent must be used as it easily enter into the plant matrix [42].