It was easy to demonstrate to the students the breakdown of
starch by amylase or proteins by pepsin. In the experiment
shown in Fig. 4, an egg was hardboiled, and the white was
separated from the yolk. The egg white was whisked using a
kitchen mixer. We scaled 10 g of whisked white and put it into
a 500-ml beaker; 200 ml of distilled water were then added,
and the beaker was placed for 15 min on a magnetic stirrer. The
solution was filtered through cotton, and the filtrate was divided
into two halves and then poured into two 250-ml beakers.
We added a solution of previously prepared pepsin to the
first beaker. The solution consisted of 2 g pepsin suspended in
100 ml of distilled water and 1.2 ml of concentrated hydrochloric
acid. Distilled water (100 ml) was added to the second
beaker as a control. Both beakers were put onto the magnetic
stirrers, and the transparency was measured as a rise in illumination
(Fig. 5).
Additionally, it was possible to investigate the effect of pH
or temperature on pepsin activity in a similar fashion. We did
not perform these experiments because of the lack of class
time