Regular articleIntermittent agitation contributes to uniformity across the bed during pectinase production by Aspergillus niger grown in solid-state fermentation in a pilot-scale packed-bed bioreactor

•Fermentations involved 27 kg of wheat bran and 3 kg of sugarcane bagasse.•Three regimes were compared: 1 (10 h), 3 (8-10-12 h) and 5 (8-10-12-14-16 h) agitations.•The best regime was three agitation events, with harvesting at 20 h.•Substrate agglomeration was avoided and the bed temperature was well controlled.•This gave uniform pectinase levels: 22 U g−1, with a sample standard error of 2 U g−1.

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 U g−1, with a sample standard deviation of 2 U g−1. We conclude that the use of intermittently-mixed packed-bed bioreactors is a promising strategy for producing pectinases in solid-state fermentation.

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