Raw eggshell membrane was obtained from commercial eggs.
The outer membranes were carefully removed manually and
washed with distilled water. Porcine gastric mucosa with an activity
of 750 U/mg proteins was purchased from Sigma Aldrich Co. (St.
Louis, US). Sodium chloride, acetic acid, sodium hydroxide and Tris
(hydroxymethyl) amino methane were purchased from Merck
(Darmstadt, Germany). All reagents used in this study were analytical
grade.