In vitro study of the inhibitory effect of Fe(II), Fe(III) and Zn(II) ions on the activity of trypsin

The effect of Fe(II), Fe(III) and Zn(II) addition on the in vitro digestibility of casein was examined using trypsin as the proteolytic enzyme. The in vitro digestibility was determined by change in trichloroacetic acid (TCA) solubility of casein and by potentiometric titration. The effect of all three metal ions was also examined on the digestion of casein heated at 80°C for 15 min prior to the enzymic hydrolysis. Heat treatments did not cause significant changes in the proteolysis of casein. The addition of Fe(II) and Fe(III) clearly slowed the proteolysis in both heated and unheated casein. The decrease in rate of proteolysis was in a direct linear relationship with the amount of Fe(II) and Fe(III) addition. The inhibitory effect of Fe(III) was more pronounced as compared to Fe(II). The addition of Zn(II) did not affect the proteolytic activity in both heated and unheated casein.