Table 3.
Keratinolytic activity testing methods.
| Substrate and unit definition | Reference |
|---|---|
| Azo-keratin | |
| The amount of enzyme yielding 0.001 (415 nm) absorbance units/h | (Gonzalo et al., 2020) |
| The amount of enzyme that increases the absorbance (440 nm) of the solution by 0.1per mL (U/mL) at the assay conditions | (e Silva et al., 2014) |
| Keratin azure | |
| The increase in absorbance at 450 nm of 0.01 after 20 min in the test reaction compared with the control reaction | (Tork et al., 2016) |
| The amount of enzyme causing an increase of 0.1 in absorbance at 440 nm in 1 min under the assay conditions | (Habbeche et al., 2014) |
| The amount of enzyme required to increase absorbance at 595 nm by 0.01 in 1 h | (Nahar et al., 2016) |
| Human hair | |
| 1 keratinase unit = 0.1 corrected absorbance at 280 nm | (Mukhopadhyay and Chandra, 1990) |
| Cow horn | |
| An increase of 0.01 absorbance unit at 280 nm ml−1 h−1 | (Dozie et al., 1994) |
| Feather powder | |
| 1 mmol tyrosine liberated per min | (Fang et al., 2013) |
| Wool top | |
| The amount of enzyme which liberates 1 μmol tyrosine/min under the assay conditions | (Iglesias et al., 2017) |
| Soluble recombinant chicken feather | |
| The amount of enzyme that produced 1 nmole of free amino groups (equivalent to arginine) as products per min at the assay conditions | (Jin et al., 2017) |