An immobilized digestive enzyme assay (IDEA) system composed of two bioreactors, one containing pepsin and the other trypsin, chymotrypsin, and intestinal mucosal peptidases, was used to assess changes in protein digestibility resulting from alkali treatment or heat treatment in the presence of fructose. The degree of amino acid racemization and the amount of lysinoalanine (LAL) formed due to alkali treatment were determined. A linear correlation (r = 0.84) was obtained between loss of digestibility and the sum of the effects of both LAL formation and racemization. The effect of Maillard reactions on both digestibility, as measured with the IDEA system, and available lysine also was assessed. A linear correlation (T = 0.87) between loss of digestibility and loss in available lysine was obtained. These data indicate that the IDEA system is quite sensitive to protein modifications resulting from alkali treatment or Maillard reactions and may be a good predictor of in vivo digestibilities of processed proteins.

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