Trypsin at a concentration of
1.6 mg/ml was maintained in an ice bath and the pH was adjusted
to 8.00 with 0.1 M NaOH and/or 0.1 M HCl. Five millilitres of
enzyme solution were then added to the protein suspension, which
was kept stirred at 37 C. The trypsin had an activity of 13,766
BAEE units/mg protein. The pH drop was recorded at 15 s after
enzyme addition and at one minute intervals for 10 min. The
enzyme solution was always freshly prepared before each series
of experiments. The percent protein digestibility (Y) was calculated
by using Eq. (1) (Hsu et al., 1977):
Y ¼ 210:464 18:1x; ð1Þ
where x is the change in pH after 10 min.