# Harnessing Agri-Food Waste as a Source of Biopolymers for Agriculture
## 2 Sources of Biopolymers
### Lignin: Extraction Methods and Applications in Agriculture
Another advantage of a two-step delignification process is the fractionation of lignocellulosic components, as the first step of both the reported studies successfully removed and fractionated the hemicellulose fraction from the biomass. Conversely, corncobs treated solely with alkaline delignification afforded a lower delignification yield (Entry 3) [24]. The enzymatic treatment of pineapple leaf waste was reported in Entry 5 [26], presenting an effective removal of lignin from the biomass with high selectivity (78.5%); unfortunately, the lignin-rich fraction obtained was not characterized. Ultrasound-assisted (UA) delignification using NaDES as green solvents is also an interesting route to explore; in Entry 2 [23], different NaDES were tested with different extraction times (60 to 120 min). When US technology was used in combination with NaDES, a higher delignification time was required; however, higher yields were achieved. This phenomenon probably occurred because NaDES are viscous and need more time for an optimal mass transfer. Overall, chlorine chloride-levulinic acid (ChLevA) afforded the highest yield of delignification and had a similar extraction yield at 60 and 120 min. Unfortunately, the recovery of lignin extracted with NaDES was very low (30 and 10 mg) for ChLA (choline chloride-lactic acid) and ChLevA, respectively, starting from 2.5 g of grape stalks, while for ChLAGly (choline chloride-lactic acid-glycerol), no lignin was recovered. This is probably caused by the depolymerization of lignin promoted by the treatment; moreover, NaDES could act as strong solubilizers towards lignin, preventing its precipitation, because deep eutectic solvents (DES) possess a very high polarity and can form H-bonds with the -OH moieties of lignin. This makes DES very efficient in lignin \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Entry** & **Biomass** & **Delignification Method** & \begin{tabular}{c} **Yield** \\ **on Total** \\ **Lignin (\%)** \\ \end{tabular} & \begin{tabular}{c} **Yield on** \\ **Biomass (\%)** \\ \end{tabular} & **Ref.** \\ \hline \multirow{6}{*}{\(1\)} & & \multicolumn{3}{c}{Hydrothermal prehydrolysis +} & 65.0 & N/A & \\  & & \multicolumn{3}{c}{Alkaline delignification} & 37.2 & N/A & \\  & & \multicolumn{3}{c}{Hydrothermal prehydrolysis +} & 37.2 & \multicolumn{1}{c}{N/A} & \\  & & \multicolumn{3}{c}{Dioxane delignification} & 67.4 & N/A & \\  & & \multicolumn{3}{c}{Phosphotungstic acid prehydrolysis +} & 67.4 & \multicolumn{1}{c}{N/A} & [22] \\  & & \multicolumn{3}{c}{Alkaline delignification} & 45.5 & \multicolumn{1}{c}{N/A} & \\  & & \multicolumn{3}{c}{Dioxane delignification} & 60.6 & \multicolumn{1}{c}{N/A} & \\  & & \multicolumn{3}{c}{Dioxane delignification} & 35.6 & \multicolumn{1}{c}{N/A} & \\ \hline \multirow{6}{*}{\(2\)} & \multicolumn{3}{c}{\begin{tabular}{c} US ChLA Assisted (60–120 min) \\ US ChLAGly Assisted (60–120 min) \\ US ChLevA Assisted (60–120 min) \\ US ChLevA Assisted (60–120 min) \\ US Alkaline Assisted (60–120 min) \\ \end{tabular} & N/A & 40–50 & \\  & \multicolumn{3}{c}{\begin{tabular}{c} US ChLAGly Assisted (60–120 min) \\ US ChLevA Assisted (60–120 min) \\ US Alkaline Assisted (60–120 min) \\ \end{tabular} & N/A & 27.96–33.88 & [23] \\ \hline \(3\) & \multicolumn{3}{c}{\begin{tabular}{c} Alkaline extraction \\ \end{tabular} } & 73.76 & N/A & [24] \\ \cline{3-6}  & \multicolumn{3}{c}{\begin{tabular}{c} Autohydrolysis + Organosolv \\ Delignification \\ Autohydrolysis + Alkaline \\ Delignification \\ Autohydrolysis + Alkaline \\ Delignification \\ \end{tabular} & 76.0 & N/A & [25] \\ \hline \(5\) & \multicolumn{3}{c}{\
\begin{tabular}{c} Waste of pineapple \\ (_Annas comosus_) leaves \\ \end{tabular} } & \multicolumn{3}{c}{
\begin{tabular}{c} Increase from _Pleurotus jamor_ \\ \end{tabular} } & 78.5 & N/A & [26] \\ \hline \multicolumn{6}{c}{N/A: not available.} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Delignification processes.