Pectinase-hyperproducing mutants of Aspergillus niger C28B25 for solid-state fermentation of coffee pulp

The aim of this study was to improve mold strains for the production of pectinases by solid-state fermentation (SSF) of coffee pulp. A screening of 248 strains, isolated in Mexico's coffee-growing areas, permitted us to select a wild strain of #Aspergillus niger$ which in 72 h attains a peak production of 27.7 U ml-1(138 U g-1 dry pulp) of pectinase measured by viscosimetry. Though the use of a selective culture medium with low water activity (aw = 0.954) with 2-deoxy-glucose (2DG) it was possible to isolate pectinase-hyperproductive mutant strains for SSF(44.5 U ml-1, 228 U g-1 dry pulp). Derepressed mutant strains that hyperproduced pectinase by submerged fermentation (SmF) were also obtained using a classic selective medium with high water activity (pectin + 2DG) with aw = 0.999. A comparison between both classes of mutants, called AW96 and AW99, respectively, points out the need to design special selective media in order to obtain strains adapted either to SSF or Smf in which the aw level would be a key selecting factor. (Résumé d'auteur