Antimicrobial and antioxidant properties of water-soluble lignin extracts obtained from ozonation of Miscanthus giganteus and Vitis vinifera in a pilot-scale reactor

Abstract

Lignin is a potential source of polyphenols with different biological activities which might be affected by the extraction or isolation process. This study investigated the effect of ozonation on the bioactive properties of water-soluble lignin extracts from Miscanthus giganteus (grass-type biomass) and Vitis vinifera (wood-type biomass). Total polyphenolic content, antioxidant activities (ABTS, DPPH and β-carotene bleaching assays), and antimicrobial properties were evaluated. Although ozonation did not improve the antioxidant activity per gram of lignin extract with any of the methods employed, it significantly enhanced extraction of antioxidants. All lignin extracts displayed significant antioxidant potential, DPPH IC50 values ranging from 7.6 to 29.0 µg/mL and ABTS ranging 64.1–154.6 mg Trolox/g extract. Miscanthus lignin extracts achieved 70.6 % β-carotene bleaching inhibition, compared with 96.2 % inhibition by BHT. Miscanthus lignin extracts exhibited better yield and antioxidant activity compared with vine shoots, likely due to their lower molecular weight and higher content of phenolic monomers. Antibacterial analysis revealed that Miscanthus lignin extracts had superior activity against Staphylococcus aureus and Escherichia coli, which was enhanced by ozonation and linked to zeta potential and compositional aspects. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for Miscanthus extracts were 3 mg/mL and 6 mg/mL, respectively. Miscanthus extracts from 160 min ozonation demonstrated better antifungal activity than vine shoots, particularly against Penicillium digitatum (MIC:12 mg/mL) compared with Botrytis cinerea (MIC:25 mg/mL). The bioactive properties of water-soluble lignin extracts from ozonated Miscanthus open up new possibilities for their potential use in food and food packaging applications.