Synergistic Microwave–Zwitterionic Natural Deep Eutectic Solvents System for Selective Fractionation of Pineapple Leaf Agro-Biomass, Enabling Multifunctional Lignin and Bioethanol Production

Abstract

This study introduces a novel, rapid, and sustainable biorefinery approach for lignocellulosic biomass valorization, employing a natural deep eutectic solvent (NADES) system composed of betaine hydrochloride and lactic acid (15:85 w/w). Within just 4 min of microwave-assisted treatment, this green solvent system enables efficient extraction of structurally pristine lignin, preserving its native architecture and unlocking its remarkable multifunctionality. The extracted lignin exhibits exceptional properties, including >95% UV shielding efficiency (transmittance < 5% in the 280–400 nm range at 0.5 mg/mL), strong antioxidant activity (69.7% DPPH inhibition at just 50 μg/mL), and potent antimicrobial effects, especially antifungal inhibition zones surpassing those of standard agents by over 75%. Simultaneously, the holocellulose-rich residue was successfully converted into bioethanol via fed-batch simultaneous saccharification and fermentation, achieving an impressive 82% of the theoretical yield. This integrated process is not only time- and solvent-efficient but also entirely free from toxic chemicals, aligning perfectly with the principles of green chemistry and circular bioeconomy. Altogether, this work positions betaine hydrochloride/lactic acid–based NADES as a transformative green solvent for holistic biomass valorization, offering a promising pathway toward sustainable production of advanced biofuels and high-value functional bioproducts.