Sustainable valorization of lemon juice pomace into bioactive pectin: Experimental cytoprotection, molecular docking, and DFT analysis against cadmium-induced oxidative damage.
Abstract
This study uniquely integrates extraction optimization, structural characterization, cytoprotection, molecular docking, and DFT analysis to valorize lemon juice pomace pectin within a circular bioeconomy framework, distinguishing it from previous work limited to peel pectin or crude extracts. The extraction process was carefully optimized to preserve the structural integrity of the polysaccharide, resulting in a high yield of galacturonic acid-rich pectin with moderate degrees of esterification. Structural analyses confirmed typical pectic features, including α-configured galacturonic acid residues as well as rhamnose, arabinose, glucose, mannose, xylose and galactose units. Therefore, PLP polysaccharides exhibited significant antioxidant activity, demonstrated by dose-dependent DPPH radical scavenging (79.5% at 10 mg/mL) and ferric-reducing antioxidant power (FRAP) of 1522.5 μmol Fe2+/L, comparable to other pomace-derived pectins. Moreover, toxicological evaluations on HEK and HCT cell lines revealed no cytotoxicity at functional concentrations and highlighted a pronounced cytoprotective effect against cadmium-induced oxidative stress. PLP significantly enhanced cell viability, reduced malondialdehyde (MDA) accumulation, and attenuated intracellular reactive oxygen species (ROS) production. Complementary in silico analyses supported these findings: molecular docking on the KEAP1 Kelch domain (PDB ID: 4L7B) showed that a galacturonic-acid tetramer engages the NRF2-binding pocket, while DFT calculations confirmed a strongly favorable carboxylate-bridged coordination of Cd2+ by pectin. Collectively, these findings position PLP as a safe and effective bioactive polysaccharide with promising potential for incorporation into functional foods, nutraceuticals, and antioxidant-enriched materials, while promoting the circular and sustainable valorization of agro-industrial by-products in line with "zero waste" principles.