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. Through the use of a selective culture medium with low water activity (a(w) = 0.954) with 2-deoxy-glucose (2DG) it was possible to isolate pectinase-hyperproductive mutant strains for SSF (44.5 U ml-1, 228 Ug-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 a(w) = 0.999. A comparison between both classes of mutants, called A W96 and A W99, respectively, points out the need to design special selective media in order to obtain strains adapted either to SSF or SmF in which the a(w) level would be a key selecting factor.