**2. Materials and Methods**

#### *2.1. Materials*

Salted wet cowhide leathers were obtained from the Timex Tannery Company, Cairo, Egypt, and then tanned, as reported by Ali et al. [39]. As for chemicals; sodium hydrogen selenite, ascorbic acid, and polyvinylpyrrolidone (PVP) were purchased from Loba Chemie, Mumbai, India. Other chemicals were of commercial grade.
