2.4. Enzyme assay
2.4.1. Radial enzyme diffusion
Keratinolytic protease activity of the crude extract was
initially detected and quantified by radial diffusion of the enzyme
through skim milk and keratin as substrate containing gel based
on a modified method of Walsh et al. (2005). Skim milk and
keratin gel plates were prepared as has been outlined in Section
2.2, with each Petri dish (diameter 85 cm) containing 20 mL of
media. For detection of keratinolytic protease activity during
screening, 0.1 mL aliquots of each sample were added to circular
wells (7 mm diameter) punched in the gels and the plates were
incubated at 45 C for 48 h. The plates were examined every 6 h
interval to measure the zones of hydrolysis by direct visual inspection
through an arbiter scale and contrast was improved by
flooding the plates with 10% tannic acid. Keratinolytic protease
activity was determined in a semi-quantitative manner by
measuring the diameters of the zones of hydrolysis observed. The
linear relationship between the diameter of the zone of hydrolysis
and the log of keratinolytic protease activity was confirmed
using a commercial protease product (SigmaeAldrich, USA)
(Walsh et al., 2005).