# Extraction of Dietary Fibers from Plant-Based Industry Waste: A Comprehensive Review
## 4 Dietary Fibers Extraction
### Pectin Extraction
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Plant Resource** & **Reference** \\ \hline \multirow{4}{*}{Conditions} & 1. & pH 2.2; 560 W—microwave power; and 120 s—duration. \\  & 2. & pH 1.8; 30 min—sonification. \\  & 3. & With cellulase: pH 4.5 (adjusted with citric acid); 47 \({}^{\circ}\)C temp; and 20 h duration. With \\  & & Celluclast 1.5 L: pH 4.5; 48 \({}^{\circ}\)C temp; and 18 h and 14 min duration. \\  & 4. & After ultrasound-assisted extraction, the sample was heated for 2 h at 86 \({}^{\circ}\)C. \\  & 5. & After enzyme-assisted extraction with cellulase, the sample was sonicated for 21 min. \\  & 6. & pH 1.9; 90 \({}^{\circ}\)C temp; and 148 min duration. \\ \hline \multirow{4}{*}{Observations} & The highest extraction yield was obtained with microwave-assisted extraction while the lowest \\  & was with enzyme-assisted extraction (with Celluclast 1.5 L). Pectin obtained via \\  & microwave-assisted extraction had a high galacturonic acid content, acceptable color parameters, \\  & increased equivalent weight, high molecular weight, and degree of esterification. Pectin obtained \\  & through ultrasound-assisted extraction also had a high galacturonic acid content, degree of \\  & esterification, and molecular weight. Pectin obtained with enzyme-assisted extraction had a \\  & lower degree of esterification and was classified as low-methovylated pectin. \\ \hline \multicolumn{2}{c}{**Gold kiwifruit (_Actinidia chinensis_)**} \\ \hline Method & Conventional citric acid extraction, water extraction, and enzyme-assisted extraction. \\ \hline \multirow{4}{*}{Conditions} & Acid extraction: pH 2.2; 1; 3 \(w/v\)—solid: liquid ratio; 50 \({}^{\circ}\)C temp; and 60 min duration. \\  & Water extraction: pH 3.7; 1; 3 \(w/v\)—solid: liquid ratio; 25 \({}^{\circ}\)C temp; and 30 min duration. \\  & Enzymatic extraction: Celluclast 1.5 L; pH 3.7; 1; 3 \(w/v\)—solid: liquid ratio; 25 \({}^{\circ}\)C temp; and \\  & 30 min duration. \\ \hline \multirow{2}{*}{Observations} & Pectin extracted with water exhibited the properties closest to its native form. The highest \\  & extraction yield was obtained with enzyme-assisted extraction. \\ \hline \multicolumn{2}{c}{**Sour orange peel**} \\ \hline Method & Microwave-assisted extraction. \\ \hline Conditions & Optimized conditions: pH 1.5; 700 W—microwave power; and 3 min—irradiation time. \\ \hline \multirow{4}{*}{Observations} & Pectin yield was 29.1% and degree of esterification ranged from 1.7% to 37.5%, which indicated \\  & low-methovylated pectin. Emulsifying activity and galacturonic acid content was 40.7% and 71%, \\  & respectively. \\ \hline \multicolumn{2}{c}{**Lemon, mandarin and kiwi peels**} \\ \hline Method & Microwave-assisted extraction and ultrasound-assisted extraction. \\ \hline \multirow{4}{*}{Conditions} & Hydrochloric acid and nitric acid—solvents. For microwave-assisted extraction: \\  & 360–600 W—microwave power; and 1, 2 and 3 min—irradiation time. \\  & For ultrasound-assisted extraction: 60 \({}^{\circ}\)C and 75 \({}^{\circ}\)C temp; and 15, 30 and 45 min—sonification. \\ \hline \multirow{4}{*}{Observations} & The highest yield was obtained for kiwi peel using hydrochloric acid (17.97% for \\  & microwave-assisted extraction at 360 W for 3 min and 17.30% for ultrasound-assisted extraction \\  & at 75 \({}^{\circ}\)C for 45 min, respectively). Generally, for all materials, microwave-assisted extraction \\  & resulted in higher extraction yields. \\ \hline \multicolumn{2}{c}{**Apple peel**} \\ \hline Method & Organic acid extraction. \\ \hline Conditions & Citric, malic, and tartaric acids—solvents; 85 \({}^{\circ}\)C temp. \\ \hline \multirow{2}{*}{Observations} & Citric acid extraction resulted in pectin with the highest molecular weight and apparent viscosity. \\  & Pectin obtained with all tested organic acids was highly methovylated. \\ \hline \multicolumn{2}{c}{**Melon peel**} \\ \hline Method & Conventional citric acid extraction. \\ \hline Conditions & Optimized conditions: pH 1; 95 \({}^{\circ}\)C temp; 10 \(v/w\) ratio; and 200 min—duration. \\ \hline \multirow{4}{*}{Observations} & The extraction yield was 29.48% and the galacturonic acid content was 48%, respectively. The \\  & emulsifying activity was 35% and at concentrations of 1% \(w/v\), the obtained pectin behaved as a weak gel. \\ \hline \end{tabular}
\end{table}