# Extraction of Dietary Fibers from Plant-Based Industry Waste: A Comprehensive Review
## 4 Dietary Fibers Extraction
### Pectin Extraction
Regarding the implemented pH values (1.5, 2, and 10) the highest amount of pectin was obtained at pH 1.5, and in systems with ethanol and EDTA [54]. The conventional acid technique was performed for pectin extraction from fresh watermelon rinds and lyophilized watermelon rinds. Pectin was extracted from alcohol-insoluble residues with boiling nitric acid (0.1 M) under reflux for a duration of one hour where the solid: liquid ratio was 1:25 (\(w/v\)). Precipitated pectin was washed with ethanol and dried under vacuum. The obtained results showed a higher yield for the fresh watermelon rinds than the lyophilized material. The obtained pectin showed a relatively high viscosity, good foaming and emulsifying properties, and could have potential applications in the food industry with great economic prospects [55]. Table 1 summarizes the studies conducted on the extraction of pectin from different plant materials using different extraction techniques. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Plant Resource** & **Reference** \\ \hline \multicolumn{3}{c}{_Musa balbisiana waste_} \\ \hline Method & Ultrasound-assisted with citric acid-mediated extraction. & \\ \hline \multirow{2}{*}{Conditions} & Optimized conditions were as follows: 323 W—ultrasound power; 3.2—pH; 28 min—extraction & [56] \\  & time; and 1:15 g/mL—solid: liquid ratio. & \\ \hline Observations & The experimental pectin yield was 8.99\% while the predicted yield was 9.02\%. & \\ \hline \multicolumn{3}{c}{**Passion fruit peel**} \\ \hline Method & Ultrasound-assisted extraction. & \\ \hline \multirow{2}{*}{Conditions} & The conditions were as follows: 644 W/cm\({}^{2}\)—power intensity; 85 \({}^{\circ}\)C temp; 1:30—dried peel: solvent ratio; and 10 min—sonication. & \\ \hline \multirow{3}{*}{Observations} & The achieved pectin yield under these conditions was 12.67\% and the esterification degree and galacturonic acid content were 60.36\% and 66.65\%, respectively. The authors made a comparison of this extraction method with the conventional method under similar conditions and the obtained pectin yield was higher with the ultrasound-assisted extraction. & \\ \hline \multicolumn{3}{c}{**Lime peel**} \\ \hline Method & Microwave-assisted and conventional extraction. & \\ \hline \multirow{2}{*}{Conditions} & Hydrochloric and citric acids—solvents; 1:20 or 1:40—peel: solvent ratio; 95 \({}^{\circ}\)C—temp for conventional method; 700 W—microwave oven power. & \\ \hline \multirow{3}{*}{Observations} & Pectin yield was higher with the conventional method with hydrochloric acid. & \\ \cline{1-1}  & Microwave-assisted extraction with citric acid resulted in pectin without loss in quality (higher equivalent weight and degree of esterification) and this method also resulted in a reduced energy consumption due to the shortened extraction time. & \\ \hline \multicolumn{3}{c}{**Sisal waste**} \\ \hline Method & Ultrasound-assisted extraction. & \\ \hline \multirow{3}{*}{Conditions} & Optimized conditions were: 61 W—ultrasonic power; 50 \({}^{\circ}\)C temp; 26 min—time of sonification; and 1:28 g/mL—solid: liquid ratio. & [59] \\ \hline \multirow{3}{*}{Observations} & The experimental pectin yield was 29.32\%, and the authors highlighted the advantages of this method due to reduced energy consumption, lower temperatures, and a shorter extraction time. & \\ \hline \multicolumn{3}{c}{_Malus domestica_ **Falticeni’ apple pomace**} \\ \hline \multirow{3}{*}{Method} & 1. Microwave-assisted extraction. & \\ \cline{1-1}  & 2. Ultrasound-assisted extraction. & \\ \cline{1-1}  & 3. Enzyme-assisted extraction. & \\ \cline{1-1}  & 4. Ultrasound-assisted extraction—heating treatment. & \\ \cline{1-1}  & 5. Enzyme-assisted extraction—ultrasound treatment. & \\ \cline{1-1}  & 6. Conventional citric acid extraction. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Studies of pectin extraction from various material sources.