# Extraction of Dietary Fibers from Plant-Based Industry Waste: A Comprehensive Review
## 4 Dietary Fibers Extraction
### \(\beta\)-Glucan Extraction  
Across the food industry, there has been an increased interest focused on the investigation of \(\beta\)-glucan extraction and purification techniques, as well as ways of incorporating \(\beta\)-glucan into food products. Techniques which achieve the highest yields and do not affect the molecular weight of \(\beta\)-glucan are favored [69]. Various extraction methods were developed for acquiring \(\beta\)-glucan from oats and barley. These methods include dry and wet processes. Milling and sieving, i.e., the dry extraction methods, serve to obtain flour fractions rich in \(\beta\)-glucan [22]. Dry fractionations include various operations, such as hammer milling, roller milling, abrasion milling, shifting, and pearling [69; 70]. The main disadvantage of these methods is the poor yield of \(\beta\)-glucan (of around 30%) [71]. Concentrations of \(\beta\)-glucan obtained through dry methods can be increased with the application of ultrafine grinding and electrostatic separation, as reported by [PERSON] et al. [72], with a 56.2% \(\beta\)-glucan concentration in the final product. Wet techniques include a solvent for a wet extract, and they comprise hot water extraction, solvent extraction, alkali extraction, and enzymatic extraction [22]. Using these methods, \(\beta\)-glucan may be concentrated up to 95% [69]. \(\beta\)-glucanase is an endogenous \(\beta\)-glucan enzyme which degrades and comments \(\beta\)-glucan. During water extraction, this enzyme may be activated, and the result produced via this technique is the lowering of \(\beta\)-glucan molecular weight and viscosity. This problem can be overcome through the inactivation of \(\beta\)-glucanase with ethanol (80% \(v/v\)) before extraction [69; 73]. Contaminants, such as starch and proteins, are usually removed using hydrolytic enzymes or through selective adsorption [74]. Problems with wet extraction can be caused by the high viscosity of \(\beta\)-glucan aqueous extracts, even at low concentrations. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Plant Resource** & **Reference** \\ \hline \multicolumn{3}{c}{**Banana peel**} \\ \hline Method & Microwave-assisted extraction (continuous and intermittent). & \\ \hline \multirow{3}{*}{Conditions} & Optimized conditions for continuous extraction: pH 3; 900 W—microwave power; and 100 s \\  & duration. & Optimized conditions for intermittent extraction: pH 3; 900 W—microwave power; and \\  & 0.5—pulse ratio. & \\ \hline \multirow{3}{*}{Observations} & The highest extraction yield for continuous extraction was 2.18\%, while for the intermittent extraction it was 2.58\%, respectively. & \\ \hline \multicolumn{3}{c}{**Lemon wet and dried peels**} \\ \hline \multirow{3}{*}{Method} & 1. & Water-based extraction. \\  & 2. & Microwave-assisted extraction. \\ \hline \multirow{3}{*}{Conditions} & 1. & Acidified water (with sulfuric acid)—solvent; pH: 1, 2, and 3; temperatures: 80, 90, and \\  & 95 \({}^{\circ}\)C; and time: 60 and 90 min. & \\  & 2. & Distilled water, 0.05 M ethylenediamine tetra acetic acid (EDTA), and 1 M sodium \\  & & hydroxide—solvents; time: 5, 10, and 15 min. & \\ \hline \multirow{3}{*}{Observations} & The maximum pectin yield with water-based extraction was obtained at 95 \({}^{\circ}\)C, pH of 1, for 90 min for both wet and dried lemon peels, at 46\% and 16\%, respectively. For microwave extraction, the maximum yield was obtained using EDTA at an extraction time of 15 min. & \\ \hline \multicolumn{3}{c}{**Banana peel**} \\ \hline Method & Ultrasound-assisted extraction. & \\ \hline \multirow{3}{*}{Conditions} & The conditions were as follows: 0.1 M of citric acid with pH 1.5, solid: liquid ratio 1:33.3 g/mL, \\  & temperature of 75 \({}^{\circ}\)C, and sonicated for 23 min. & \\ \hline \multirow{3}{*}{Observations} & Using the optimal extraction conditions, the achieved pectin yield was 6.08\%. The obtained \\  & pectin was high-methoxy pectin with improved gelling time. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cont.