A wholly biological method for galactaric acid production from pectin by the combination of enzymatic hydrolysis and resting-cell catalysis

Abstract

Galactaric acid (GA), an attractive biomass-based platform compound produced from galacturonic acid (GalA), has gained considerable attention in industry due to its application as a precursor for various polymers. Currently, GA is oxidized from galactose using nitric acid or GalA using bromine but its low selectivity and yield limit its industrial-scale production and application. The present study first sought to produce GA without any by-product from the monomeric compound of GalA obtained from pectin hydrolysis in an eco-friendly manner using Gluconobacter oxydans (G. oxydans) as the research object. In this regard, a wholly biological method was designed by combining enzymatic hydrolysis, electrodialysis, and resting-cell catalysis with pectin as a raw material to enhance its production. After a series of pectin degradation experiments, including degradation scheme screening and enzyme dosage and substrate concentration optimization, a pectin degradation rate of 96.9% was finally achieved. Furthermore, the resting-cell catalytic efficiency of the enzymatic hydrolysate purified by electrodialysis was consistent with that of the simulated solution, which was 20.7% higher than that of the untreated enzymatic hydrolysate. Additionally, the experiment confirmed that pH significantly influenced the catalytic and oxidative efficiency of resting-cell catalysis. Finally, 2520 mg L⁻¹ of GA was stably produced by resting-cell catalysis in the broth at pH 4.0 for 72 h, suggesting it to be a promising green approach for industrial bio-production of GA.