Whole yeast cell synthesis of 5-hydroxymethylfurfural-derivatives from apple waste processed by green technologies

The transition to renewable resources and bioprocesses is essential to address climate change and meet energy demands. Biorefineries offer a sustainable solution by valorising agro-industrial wastes, such as apple pomace, a by-product of the juice and cider industries. This study presents an efficient process to produce 5-hydroxymethylfurfural (HMF) derivatives using deep eutectic solvent (DES) and microwave-assisted heating. Under optimal conditions (160 °C, 30 min, and 50 % Choline Chloride: Lactic acid (ChCl:LA) DES) HMF yield reached 34.6 %. Engineered Saccharomyces cerevisiae strains expressing HMF oxidase enzyme facilitated the bioconversion of HMF from apple pomace hydrolysate into high-value derivatives, particularly furandicarboxylic acid (FDCA), a precursor for bio-based polymers. The best-performing strain achieved 10.8 mM FDCA and 15.5 mM 5-formyl-2-furancarboxylic acid (FFCA) under optimised conditions. This integrated approach-combining catalytic HMF production via DES microwave-assisted technology with microbial biocatalysis-offers a sustainable pathway for agro-waste valorisation and the production of renewable chemicals.