Green valorization of garlic peel waste using halophilic laccase for efficient biomass delignification and biorefinery applications

Abstract

Lignocellulosic biomass, mainly composed of cellulose, hemicellulose, and lignin, is an abundant renewable resource in agricultural and forestry residues. In contrast to cellulose and hemicellulose, lignin remains underutilized due to its complex structure. In this study, a halophilic bacterium, Virgibacillus salarius was isolated, and its laccase production was optimized for delignification. Using response surface methodology (RSM), a maximum laccase activity of 392.0 U L⁻¹ was achieved. This enzyme demonstrated high efficiency, reducing lignin content in garlic peel from 32.4 to 3.6% and increasing cellulose content from 42.1 to 44.1%. Additionally, the delignified biomass exhibited increased crystallinity and a porous surface, enhancing its suitability for further processing. The delignification process yielded valuable by-products, including 3-hydroxybenzoic acid (a food preservative and flavor enhancer) and aromatic compounds such as 2-methoxyphenol (guaiacol) and ethyl-2-methoxyphenol (homovanillin), which are widely used as flavoring agents. These findings emphasize the potential of V. salarius laccase in sustainable biomass conversion for industrial applications.