Extrusion-Cooking of Protein-Enriched Cookies

Time-Temperature Measurements and Maillard Reactions

Abstract

A mix containing 42% wheat flour, 20% corn starch, 20% sucrose, 11% soy protein isolate, 6% sodium caseinate, and 1% NaCl was texturized in a corotating twin screw Creusot-Loire BC-45 extruder. Temperature and pressure of the mix measured just before the die, and distribution of residence time measured using erythrosin, were reported as a function of water content, feed rate, screw rotation, and barrel temperature. Under usual operating conditions, 13% water, 40 kg/hr, and 80 rpm, the mix progressed without bachmix along the first 400mm of screw length in 10 sec; in the last 150mm section, where the reverse screw element was located, the melted mix remained from 25 to 70S, at about 200°C. Sucrose hydrolysis during extrusion, as determined by the invertase-glucose oxidase method, varied from 2 to 10% of initial sucrose. Loss in FDNB-reactive lysine caused by Maillard reaction was from 0 to 44%, depending mainly on temperature and water content, and not on screw rpm; lysine loss decreased when water content increased from 13% to 18%, even when the barrel temperature was increased so as to keep the temperature of the flour mix constant. Molar ratio of sucrose to lysine loss was always≥1.2. Decreasing the pH of the flour mix with citric acid or glucono-δ-lactone enhanced the loss of FDNB-reactive lysine. Severe conditions of extrusion-cooking also caused a decrease in cystine and arginine.