Lignocellulosic Biomass as Source for Lignin-Based Environmentally Benign Antioxidants

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Food Science

Background:

• Technical lignin, a byproduct of pulping, possesses antioxidant properties but its complex structure limits applications.
• Antioxidants are crucial for preserving oxygen-sensitive products like food, cosmetics, and biomedicines.
• Lignin's heterogeneity and polydispersity have hindered its use as a natural antioxidant.

Purpose of the Study:

• To investigate the antioxidant capacity of technical lignin.
• To evaluate the impact of purification on lignin's structure and antioxidant activity.
• To compare the antioxidant potential of lignin from different sources and pulping processes.

Main Methods:

• Antioxidant activity assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay.
• Lignin structure and purity analyzed via UV/Vis, FTIR, HSQC, 31P NMR, SEC, and XRD.
• Differential scanning calorimetry (DSC) used to determine glass transition temperature.

Main Results:

• Double-fold selective extraction yielded lignin fractions with narrow polydispersity (3.2⁻1.6) and enhanced properties.
• The glass transition temperature of the purest lignin fraction increased from 123 °C to 185 °C.
• Kraft lignin fractions showed DPPH inhibition of 62–68%, higher than beech (42%) and mixed spruce/pine lignin (64%).
• Total phenol content (TPC) ranged from 26–35% for kraft lignin, comparable to beech (33%) and mixed spruce/pine lignin (34%).
• Storage decreased TPC but increased DPPH inhibition.

Conclusions:

• Purification significantly improves lignin structure and antioxidant capacity.
• Technical kraft lignin, particularly after purification, demonstrates potent natural antioxidant properties.
• Lignin's antioxidant potential is influenced by biomass source, pulping method, and purification degree, offering a sustainable alternative for product preservation.