2.5. Protein digestibility
Protein digestibility (PD%) was determined as described by
Rudloff and Lönnerdal (1992) with modifications. Approximately
2.3 g of sample was dispersed in 10 mL of distilled water, adjusted
to pH 2 with 6 mol/L HCl and pepsin was added in order to have 1/
15 and 1/20 enzyme/protein ratio. The samples were kept in dark,
in a shaking water bath at 37 C for 30 min. Then, the pH was
gradually increased to 7.0 with 1 mol/L NaHCO3 and 2.5 mL of
pancreatin solution (0.4 g/100 mL 0.1 mol/L NaHCO3) was added
and incubated for 1 h at 37 C. Digested samples were immediately
placed in boiling water for 10 min to inactivate the enzymes. On
5 mL aliquot of the digested samples, 5 mL of 200 g/L TCA was
added, stayed 30 min at 4 C and centrifuged 30 min at 5000 g. PD
% was defined as non protein nitrogen (NPN) after digestion, in
relation to the total nitrogen content (TN).
PD% ¼ 100 NPN=TN