The absorbance of the deep orange colour produced by incubating protein hydrolysates with trinitrobenzene sulphonic acid was used to follow the liberation of free amino groups. Five animal and five plant proteins were hydrolysed with pepsin-pancreatin and papain-pronase E and aliquots were taken every 4 hr. To facilitate proteolysis the proteins were presolubilized in 0.05 M HCl at 70°C for 2 hr with 1.0 ml 0.8% mercapto-ethanol added to reduce disulphide bonds. An increase in absorbance occurred in all enzymatic digests between 8-20 hr incubation. No further hydrolysis took place after 20-28 hr incubation. The extent of the hydrolysis in vitro correlated with in vivo measurements of digestibility and so may serve as a more rapid predictor of digestibility.
Rapid in vitro enzyme predictive model for the in vivo digestibility of food proteins. J. Available from: https://www.researchgate.net/publication/229952359_Rapid_in_vitro_enzyme_predictive_model_for_the_in_vivo_digestibility_of_food_proteins_J [accessed Dec 28, 2015].