Kinetics of lysine and other amino acids loss during extrusion cooking of maize grits

Abstract

Maize grits were extrusion-cooked in a conical, counter-rotating twin-screw extruder at different barrel temperatures, feed moistures, and screw speeds. Residence time distribution was measured by a dye tracer technique. Experiments with lysine-fortified maize grits showed a 1st order reaction for lysine loss. A detailed kinetic study has been performed for the losses during extrusion cooking of lysine, cystine, and arginine. The 1st-order rate constants were dependent mainly on product temperature and feed moisture, whereas screw speed had no influence. Activation energy of lysine, arginine, and cystine loss was 127, 68, and 76 kJ/mol, respectively. Shear stress significantly affected the rate constants of amino acids loss in extrusion cooking.