# Extraction of Dietary Fibers from Plant-Based Industry Waste: A Comprehensive Review
## 5 Conclusions and Future Perspectives
\begin{table}
\begin{tabular}{c c} \hline \hline  & **Plant Resource** & **Reference** \\ \hline \multicolumn{3}{c}{**Orange peel**} \\ \hline Method & Extraction with sodium sulfite and sodium metabisulfite. \\ \hline \multirow{3}{*}{Conditions} & The applied conditions were as follows: 98 \({}^{\circ}\)C temp; 7.5:1—liquid: solid ratio. \\  & Bleaching treatment was performed under an alkaline medium, slightly acid medium, and \\  & hydrogen peroxide at 25 \({}^{\circ}\)C temp for 240 min, 120 min, and 60 min, respectively. \\ \hline \multirow{3}{*}{Observations} & The optimum yields were 45.2\% and 40.4\% for sodium metabisulfite and sodium sulfite, \\  & respectively. The results showed good purity, whiteness, water retention, molecular weights, and \\  & low crystallinities. \\ \hline \multicolumn{3}{c}{**Lemon (_Citrus limon_) seeds**} \\ \hline Method & Water extraction of cellulose and preparation of cellulose nanocrystals through sulfuric acid \\  & hydrolysis, ammonium persulfate oxidation, and TEMPO oxidation. \\ \hline \multirow{3}{*}{Conditions} & Extraction of cellulose from lemon seed powder with water at 80 \({}^{\circ}\)C for 2 h. Lignin was removed \\  & with 59 \(\%\)\(w/v\) NaClO\({}_{2}\), pH 3.8-4, at 75 \({}^{\circ}\)C for 5 h. Hemicellulose and residual lignin were \\ \cline{1-1}  & removed with 10\% \(w/v\) NaOH at 30 \({}^{\circ}\)C for 12 h. \\ \cline{1-1}  & Sulfuric acid (64\% \(w/w\)) hydrolysis was conducted for 1.5 h at 45 \({}^{\circ}\)C. \\ \cline{1-1}  & Ammonium persulfate (1 M) oxidation was performed at 70 \({}^{\circ}\)C for 14 h. \\ \cline{1-1}  & TEMPO oxidation was conducted with the TEMPO/NaBr/NaClO system in water (pH 10) for 4 h. \\ \hline \multirow{3}{*}{Observations} & The lemon seed cellulose yield was 14.6\% (\(w/w\)). \\ \cline{1-1}  & The yield of cellulose nanocrystals obtained with sulfuric acid hydrolysis, ammonium persulfate \\ \cline{1-1}  & oxidation, and TEMPO oxidation was 27.61\%, 13.02\%, and 52.01\%, respectively. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._of extraction methods should be examined. Subsequently, the ones with the highest capability of exhausting by-products and achieving maximum product quality should be chosen. Application of green extraction techniques, which do not use solvents that are harmful to the environment and minimize energy use, in combination with the use of plant-based industrial waste to extract components of interest, would provide a foundation for sustainable food production with an ecologically friendly approach. Investigation of new industrially relevant extraction techniques is expensive; however, reducing the time of extraction, energy consumption, and reagent expenses, while increasing extraction yields and achieving improved quality of the final products, can result in the economic and commercial validation of these novel methods since they can achieve profitability in the long run. Although numerous studies have been performed on dietary fiber extraction by implementing new extraction techniques using various plant-based by-products, which resulted in promising results both in terms of yield and product quality, there are still many challenges and obstacles to their industrial applications. Some of these challenges are the lack of providers of such equipment, the previously mentioned high costs, and also the lack of professional operators, as well as programs for their training and education. Also, not enough is known about the applicability of these techniques after their scale-up to industrial production capacities, but successful laboratory studies on various plant-based by-products are an invitation to industries to cooperate with the scientific sector. Conceptualization, M.K., D.S. and J.S. ; investigation, I.B., J.B., D.S. and A.P. ; data curation, I.B., J.B. and A.P. ; writing--original draft preparation, I.B. ; writing--review and editing, M.K., A.P. and J.S. ; visualization, M.K., D.S. and J.S. ; supervision, M.K., J.B. and A.P. ; project administration, M.K. ; funding acquisition, M.K.