There is an abundant literature about cellulase assays. Beside Congo red and filter paper assays, there are also chromogenic or fluorogenic substrates, such a p-nitrophenyl-beta-cellobioside. However, to my knowledge, there is no easy universal assay that can predict the activity of a crude cellulase prep on a different substrate. If you want to know the activity on filter paper, use filter paper; if you want to know the activity on Avicel, use Avicel etc. Congo red is quick and will give you an idea about endoglucanase activity, butit is worthless for predicting the activity against crystalline cellulose.
Mmm...I want a quick method about cellulase activity (using microcrystalline cellulose as substrate), because I have five points in kinetic curve that I have to compare for expression analysis. So, An idea about the total activity of cellulases is very helpful...
But I would like to know if the results of the screening are reliable (cause with the soften cellulose we have reducing sugars and that interferes with the cellulolityc activity)