# Extraction, Characterization, and Applications of Pectins from Plant By-Products
## 5 Techno-Functional Properties and Application of Pectin
### Emulsion  
Oil-in-water (\(o/w\)) emulsions are interesting delivery systems of lipophilic bioactive compounds, such as vitamins and antioxidants [134]. These emulsions are thermodynamically unstable systems, consisting of dispersed oil droplets in a continuous, aqueous phase. Emulsifiers are often added to kinetically stabilize \(o/w\) emulsions. The type of emulsifiers used depends on the product shelf life, functionality, and stability. In the emulsification process, the emulsifier adsorbs at the surface of the fine droplets, which is created by mechanical homogenization, and protects them from coalescing with neighboring drops by forming a steric stabilizing layer. The most commonly used types of emulsifier in the food industry are small-molecule surfactants, biopolymers, and phospholipids [135]. Emulsifying activity (EA) and emulsion stability (ES) are two parameters used to characterize an emulsion. They are defined, respectively, as the maximum amount of oil that can be emulsified by a fixed amount of the emulsifying agent and as the rate of phase separation of water and oil during storage of the emulsion. Good emulsion stability means that the size distribution and the spatial arrangement of droplets do not change significantly during the observation time. Rheological properties of food emulsions play an important role in the stability as well as in the mouthfeel and texture of these products [136]. Pectin has been introduced as an emulsion-stabilizing agent, mainly by increasing the viscosity of the continuous phase [137]. A high viscosity of the aqueous continuous phase can reduce oil droplet coalescence and flocculation [137]. The ability of pectin to increase the viscosity of the aqueous phase is partly caused by its HG domain. The contribution of HG to emulsion stabilization might be dependent on the HG/RG-I ratio [138]. Therefore, HG-rich pectins reveal higher solution viscosity, as compared to RG-I-rich pectins [118]. The amount and pattern of distribution of hydrophilic and hydrophobic groups in pectin determine the solubility and rheological properties of liquid food products to which pectin has been added. Different extraction methods lead to the production of pectins that ultimately produce different viscosities in aqueous solution, affecting emulsion characteristics [77]. Additionally, the presence of high hydrophobicity  
\begin{table}
**Pectin Sources** & **Measurement Conditions** & **WHC** & **OHC** & **References** \\ \hline Walnut & \(1\) g powder/10 mL deionized water & 5.84 g water/g & 2.22 g oil/g powder & [132] \\ Walnut & mixing for 1 min & powder & & \\ centrifuging at 3000\(\times\)\(g\) for 20 min & & & \\ \hline Commercial apple & \(1\) g powder/60 mL deionized water & & \\ pectin & incubating at room temperature for 24 h & 2.00 g water/g & \\ centrifuging at 14,000\(\times\) g for 1 h & powder & & \\ \hline Commercial citrus & \(1\) g powder/60 mL deionized water & & \\ pectin & incubating at room temperature for 24 h & 10.00 g water/g & \\ centrifuge at 14,000\(\times\)\(g\) for 1 h & powder & & \\ \hline By-product from & \(1\) g powder/60 mL deionized water & & \\ olive oil production & incubating at room temperature for 24 h & 1.87 g water/g & \\ centrifuge at 14,000\(\times\)\(g\) for 1 h & powder & & \\ \hline Pistachio green hull & \(1\) g powder/10 mL deionized water & & \\ mixing for 1 min & & powder & \\ centrifuging at 3000\(\times\)\(g\) for 30 min & & & \\ \hline \hline \end{tabular} \begin{tabular}{c c c c} \hline \hline \end{tabular}  \ \begin{tabular}{c c c} \hline \hline \hline \end{tabular} \begin{tabular}{c c} \hline \hline \hline \end{tabular}  \begin{of the protein moieties linked to the arabin galactan part of pectin and its methyl, acetyl, and ferulic acid ester contents provide the ability to adsorb at the oil-water interface [135]. These compounds play a role in the initial stage of emulsion formation, while the next stage is emulsion stabilization.