# Extraction, Characterization, and Applications of Pectins from Plant By-Products
## 4 Commercial Pectins
### Pectin from Watermelon  
Several studies have analyzed the pectin extracted from watermelon rind. The extraction of this pectin was carried out with conventional, enzymatic, and microwave-assisted extractions. Conventional extraction of watermelon rind using nitric acid, for 45 min, pH 1.65, with a solid to liquid ratio of 0.258 g/mL using a water bath, has shown an extraction yield of 12%. Moreover, pectin yield for enzymatic extraction of watermelon rind using Fibrilase and Multifect XL at solid to liquid ratios of 0.18 and 0.25 g/mL using enzyme loadings of 4.6 and 3.0 FPU/g, respectively, at 50 \({}^{\circ}\)C for 15 h in 50 mM citrate buffer could reach 20%. The highest galacturonic acid content was found using acid extraction (-70%) and all the pectins obtained were LM [91; 92; 93]. Extraction of pectin from watermelon by MAE, at a power of 500 W, pH of 1.5, time of 7 min, and a solid-liquid ratio of 1:20, led to yields between 19.1 and 19.6%. The pectins extracted had DEs between 44.3 and 48.7%, molecular weights between 143,400 and 154,300 Da, and GalA contents between 74.6 and 76.1%. Yields of 17.4-17.6%, ash content of 1.6-1.9%, GalA contents of 78.3-82.8%, DE of 38.2-41.2%, and Mw of 110,600-128,000 Da were reported for pectins extracted by CHE. CHE was carried out in the following optimum conditions: pH of 1.0, temperature of 90 \({}^{\circ}\)C, time of 150 min, and solid-liquid ratio of 1:20 [70]. The effect of pretreatment (drying of watermelon rind) was evaluated by Petkowicz et al. (2017) [6]. They reported that the pectin obtained from fresh and lyophilized watermelon (FW and LW) rind has a high degree of methyl esterification (60%). FW and LW were able to produce a lower dynamic surface tension and higher foaming ability than gum arabic at the same concentration. The viscosity of the FW sample was higher than that of LW sample despite their similar molar mass [6]. Maran et al. (2014) showed that the optimum conditions to obtain the maximum yield (25.79%) of pectin is microwave power of 477 watts, time irradiation of 128 s, with a pH of 1.52 [76]. Additionally, Rasheed et al. (2008) reported that the pectin extracted from watermelon peel with a yield of 15.19% was an LM pectin (DE = 44.3) [43]. Hartati et al. (2014) found that the optimum MAE conditions for the highest extraction yield of 11.25% were achieved with a 15 min extraction time in 0.5 M sulfuric acid solution with a solid-liquid ratio of 1:08. The lower extraction yield observed for extraction with higher power could be due to pectin degradation, as reported previously [92]. The isolated pectins were HM pectins (DM higher than 50%). These results contrast with those reported by Jiang et al. (2012). Indeed, only LM pectins were obtained from watermelon rind extractions by these authors [6]. Korish (2015) extracted pectin from _Citrullus lanatus_ var. Colocynthoides (C. var. Colocynthoides), a wild type of watermelon, only cultivated for seeds. The highest yield (19.75% \(w\)/\(w\)) was achieved using a solid-liquid ratio of 1:15, pH 2, and 85 \({}^{\circ}\)C, for 60 min. The galacturonic acid content and methylation degree of extracted pectin were 76.84 and 55.25%, respectively. The neutral sugars of the extracted pectin were galactose (9.07% (\(w\)/\(w\) of pectin)), followed by arabinose (4.88%), rhamn (2.54%), glucose (2.52%), mannose (0.22%), and xylose (0.56%) [93]. Watermelon rind can be considered as a valuable source of pectin because it contains a significant amount of this polysaccharide (Tables 1 and 2), although it is lower than that of citrus, the main commercial source of pectin. According Table 3 and Table 4, watermelon pectin can have emulsifying activity and good water-holding (WHC) and oil-holding (OHC) capacities. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Feen Sources**} & \multicolumn{1}{c}{\multirow{2}{*}{**Testments**}} & \multicolumn{1}{c}{\multirow{2}{*}{**Solvents**}} & \multicolumn{1}{c}{**Extraction Conditions**} & \