Conversion of citric pectin into D-galacturonic acid with high substrate loading using a fermented solid with pectinolytic activity

•Fermented solid with pectinolytic activity was produced using Aspergillus oryzae.•The fermented solid was added directly to pectin to produce D-galacturonic acid.•D-galacturonic acid yield was 247 mmol L−1 from a 10% w/v pectin solution.•This is the highest reported D-galacturonic acid concentration for pectin hydrolysis.•This process can be used to produce D-galacturonic acid in citrus-waste biorefineries.

Citrus pulp is a waste product of orange juice processing. Pectin can be extracted from this pulp and used in the food industry. However, citrus pulp is produced in such large amounts that the pectin it contains is far in excess of the current world pectin market. An alternative strategy would be to hydrolyze this excess pectin to liberate D-galacturonic acid (D-galA), which can then be converted into several platform chemicals. We report, for the first time, the hydrolysis of pectin by the direct addition of “pectinolytic fermented solids”. These solids were produced by solid-state fermentation of a 30:70 mixture, by dry mass, of ground sugarcane bagasse and orange peels, using a strain of Aspergillus oryzae isolated from rotting passion fruit peels. With the addition of this lyophilized fermented solid to a 10% w v−1 pectin solution, we obtained 247 mmol L−1 of D-galA in the hydrolysate, this being the highest D-galA concentration yet reported. Since the direct addition of fermented solid to the reaction mixture avoids the need for extraction and recovery steps, our process has potential to provide low cost of pectinases for use in citrus-waste biorefineries.