# Extraction of Dietary Fibers from Plant-Based Industry Waste: A Comprehensive Review
## 4 Dietary Fibers Extraction
### \(\beta\)-Glucan Extraction
Also, low pH values and the presence of endogenous enzymes can cause a reduction in the molar mass of \(\beta\)-glucan [74]. [PERSON] et al. [22] performed \(\beta\)-glucan extraction from oat flour using subcritical water extraction under optimized conditions (200 \({}^{\circ}\)C--extraction temperature, 10 min--extraction time, 4.0--solvent pH, and 425-850 \(\upmu\)m--particle size). Extraction yield was 6.98 g/100 g oat flour, which was twice the yield value achieved using hot water extraction at 60 \({}^{\circ}\)C for 3 h [22]. Hot water extraction was performed on the oat bran to extract \(\beta\)-glucan. Milled oat bran was first mixed with ethanol to deactivate \(\beta\)-glucanange, followed by the addition of water (55 \({}^{\circ}\)C) to the mixture and mixing for 2 h. After centrifugation, the supernatant was adjusted to pH 8.5 using NaHCO3 and then to pH 4 with citric acid. The slightly alkaline solution and acid solution were necessary for the separation of proteins and fibers. Finally, \(\beta\)-glucan was precipitated with ethanol and the yield obtained was 5.3% [75]. Barley (_Hordeum vulgare_ L.) \(\beta\)-glucan was extracted with subcritical water at temperatures of 130-170 \({}^{\circ}\)C and under pressures of 10-40 MPa in a semi-batch system. UV-Vis spectra and FT-IR spectra confirmed the extraction of \(\beta\)-glucan. These authors improved their extraction process with CO2 addition and their results showed that the extraction yield was significantly increased [76]. The same group of authors found that the entire amount of water-soluble \(\beta\)-glucan was extracted at 170 \({}^{\circ}\)C [77]. Table 2 lists the investigations conducted on \(\beta\)-glucan extraction from various material sources. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Plant Resource** & **Reference** \\ \hline \multicolumn{3}{c}{**Highland barley**} \\ \hline Method & Alkaline-acid-alcohol extraction method. & \\ \hline \multirow{3}{*}{Conditions} & Barley bran was mixed with water at pH 8 adjusted with NaOH and incubated for 2.5 h at 80 \({}^{\circ}\)C. \\  & The mixture was centrifuged two times (after the first one, the pH of the supernatant was \\  & adjusted to 4.5 with HCl, and after the second, the supernatant was reduced at 100 mL and mixed \\  & with ethanol) and after 10 h of incubation at 4 \({}^{\circ}\)C the precipitate was freeze dried. & \\ \hline \multirow{3}{*}{Observations} & \(\beta\)-glucan extract showed great thermal and pH stability and its solubility was influenced by \\  & temperature. & \\ \hline \multicolumn{3}{c}{**Hull-less barley bran**} \\ \hline \multirow{3}{*}{Method} & 1. & Ultrasound-assisted extraction. \\  & 2. & Microwave-assisted extraction. \\  & 3. & Microwave-ultrasound-assisted extraction. \\  & 4. & Hot water extraction. \\ \hline \multirow{3}{*}{Conditions} & 1. & A 1:25 \(w\)/\(v\)—solid: liquid ratio; 50\%—amplitude level; 20 min duration; and 50 \({}^{\circ}\)C temp; \\  & 2. & A 1:25 \(w\)/\(v\)—solid: liquid ratio; 3 min duration; and 800 W—microwave power; \\  & 3. & A 1:25 \(w\)/\(v\)—solid: liquid ratio; microwave heating for 1.5 min at 800 W; and sonicating for \\  & 10 min at 50 \({}^{\circ}\)C; \\  & 4. & A 1:15 \(w\)/\(v\)—solid: liquid ratio; 80 \({}^{\circ}\)C temp; 2 h duration; enzymatic treatment for \\  & removing starch and protein—\(\alpha\)-amylase and trypsin; precipitation in ethanol for 12 h; and \\  & freeze drying. & \\ \hline \multirow{3}{*}{Observations} & The microwave-ultrasound-assisted extraction resulted in the highest extraction yield (2.16\%) in \\  & the shortest amount of time. \(\beta\)-glucan obtained with this method had the highest apparent \\ \cline{1-1}  & viscosity, stronger foam stability and emulsifying properties than \(\beta\)-glucan obtained with \\ \cline{1-1}  & ultrasound-assisted extraction, which had the stronger foaming capability. & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Studies of \(\beta\)-glucan extraction from various material sources.