Solid-state fermentation could be used to produce low-cost pectinases that could then be used to saccharify pectin in citrus waste biorefineries. Recently, we produced pectinases in a pilot-scale packed-bed bioreactor, growing Aspergillus niger on a substrate mixture consisting of 27 kg of wheat bran and 3 kg of sugarcane bagasse (dry mass). However, the agglomeration of particles and shrinkage of the bed created preferential flow paths, leading to overheating within the bed and poor uniformity of pectinase levels at the end of the fermentation. In the current work, we used intermittent agitation as a strategy to minimize agglomeration, comparing one agitation (10 h), three agitations (at 8, 10 and 12 h) and five agitations (every 2 h from 8 to 16 h). The pectinase activity in the bed was uniform after agitation, but poor uniformity occurred when the bed was left unmixed for more than 10 h. The best regime was that with three agitations: For 15 samples removed from different vertical and horizontal positions of the bed at 20 h, the average pectinase activity was 22 Ug(-1), with a sample standard deviation of 2 Ug(-1). We conclude that the use of intermittently-mixed packed-bed bioreactors is a promising,strategy for producing pectinases in solid-state fermentation. (C) 2017 Elsevier B.V. All rights reserved.

Pectinases can be used in citrus waste biorefineries to hydrolyze the pectin in citrus pulp to produce D-galacturonic acid, a potential platform chemical. Solid-state fermentation has the potential to produce low-cost pectinases for such biorefineries, but it is difficult to control the process at large scales. In the current work, Aspergillus oryzae was cultivated in a pilot-scale packed-bed bioreactor, on 15 kg of a substrate containing 51.6% citrus pulp and 48.4% sugarcane bagasse (w/w, dry basis). The sugarcane bagasse gave a high bed porosity and ensured a stable bed structure, avoiding problems of bed shrinkage and the formation of compact agglomerates within the bed. As a result, bed temperatures were controlled to within 1 degrees C of the inlet air temperature and pectinase yields of 33-41 U g(-1) were obtained across the bed. When the fermented solids were dried and added directly to a pectin solution, they gave a profile for the release of D-galacturonic acid similar to that obtained with a commercial pectinase. These results show the potential for using solid-state fermentation to produce pectinases in a citrus waste biorefinery, with subsequent direct addition of the fermented solids to produce D-galacturonic acid from the pectin contained in the citrus pulp. (C) 2016 Elsevier B.V. All rights reserved.