Comparative evaluation ofAspergillus nigerstrains for endogenous pectin depolymerization capacity and suitability for D-galacturonic acid production

Pectinaceous agricultural residues rich in d -galacturonic acid ( d -GalA), such as sugar beet pulp, are considered as promising feedstocks for waste-to-value conversions. Aspergillus niger is known for its strong pectinolytic activity. However, while specialized strains for production of citric acid or proteins are openly available, this is not the case for the production of pectinases. We therefore systematically compared the pectinolytic capabilities of six A. niger strains (ATCC 1015, ATCC 11414, NRRL 3122, CBS 513.88, NRRL 3, N402) using controlled batch cultivations in stirred-tank bioreactors. A. niger ATCC 11414 showed the highest polygalacturonase activity, specific protein secretion and a suitable morphology. Furthermore, d -GalA release from sugar beet pulp was 75% higher compared to the standard lab strain A. niger N402. Our study therefore presents a robust initial strain selection to guide future process improvement of d -GalA production from agricultural residues and identifies the most suitable base strain for further genetic optimizations.