I am working on the production of the pectinase enzyme by Aspergillus spp. by the Solid-state fermentation (SSF) . The medium contained 2 g dry citrus peel 8 g of dry wheat bran. The solid media were inoculated with 107 spores per gram of dry substrate and incubated at 30°C for 72 h. For the extraction, 100 mL of acetate buffer (0.2 M, pH 4.5) was added per gram fermented solids and the mixture was incubated on an orbital shaker at 30°C for 45 min at 180 rpm. The crude extracts were centrifuge and filtered using Whatman nu1 filter paper. The filtrate was stored at 4 °C.

In assessing the pectinase with DNS method, negative control (enzyme (crude extracts) with DNS, without substrate) is positive reaction?

Is there a disruptive factor in the crude enzyme? How can I fix it?