Thiamine destruction during extrusion cooking as an indicator of the intensity of thermal processing

Abstract

SummaryAssessment of the intensity of high temperature‐short time (HTST) extrusion cooking was studied by measuring the extent XA of thiamine destruction. Small quantities of thiamine hydrochloride (0.1–0.7 g per 100 g) were mixed with wheat flour (containing ∼ 14% water) prior to extrusion experiments. Results indicate that thiamine destruction follows an apparent first‐order reaction and that the rate constant K of destruction, calculated from near isothermal extrusion experiments at 133, 142 or 152°C (product temperature), follows an Arrhenius relationship with an activation energy of 49.9 kJ/mol. K values were calculated from experimental determination of XA and of the residence time distribution (RTD) in the effective heating zone of the extruder.The influence of product temperature (just before the die), water content during extrusion and speed of screw rotation on the overall K (for non‐isothermal extrusion experiments) was determined and analysed by multiple regression. Results show that thiamine destruction XA can be predicted by means of a linear mathematical model.Each experimental XA value can be used, in combination with Arrhenius equation constants and RTD, to express a given extrusion process in terms of equivalent isothermal temperature and equivalent plug flow residence time.