Microwave–vacuum extraction and electrospinning-based stabilization of tomato pomace phenolics in citric acid-modified gelatin nanofibers

Abstract

Phenolic-rich extracts were recovered from industrial tomato pomace using microwave–vacuum extraction (MVE) and incorporated into gelatin nanofibers via electrospinning. Optimal extraction conditions (1/10 w/v solid-to-solvent ratio, 4 min, 400 mmHg, 100% microwave power) yielded a total phenolic content (TPC) of 4.174 mg GA/g dry material and antioxidant activities of 0.225 mg DPPH/g and 4.417 mg GA/g (CUPRAC). Gelatin nanofibers (20% w/w) were loaded with tomato pomace extract (0.3–1.0% w/v), with and without citric acid (CA) as a cross-linker. CA markedly improved fiber morphology, producing smooth, bead-free nanofibers with average fiber diameters of 95.6 ± 7.0, 123.4 ± 7.4, and 129.0 ± 4.7 nm at 10%, 15%, and 20% gelatin concentrations, respectively. Higher extract concentrations significantly increased TPC, CUPRAC, and loading efficiency (p < 0.05), with the highest loading efficiency (83.7%) and TPC (3.450 mg GA/g) achieved at 1.0% extract with CA. FTIR analysis suggested structural reorganization of the gelatin network through enhanced intermolecular interactions involving hydrogen bonding and possible esterification, which contributed to improved jet stability, fiber uniformity, and phenolic retention. These results demonstrate that CA-modified electrospun gelatin nanofibers provide an interaction-driven protein-based carrier system for stabilizing phenolic compounds recovered from tomato pomace and highlight the potential of integrating MVE with electrospinning as a sustainable food-oriented strategy for valorization of agro-industrial by-products and development of functional antioxidant delivery systems.