QUANTITATIVE MEASUREMENT OF EXTRUSION-INDUCED STARCH FRAGMENTATION PRODUCTS IN MAIZE FLOUR USING NONAQUEOUS AUTOMATED GEL-PERMEATION CHROMATOGRAPHY

Automated gel-permeation chromatography (GPC), with application of the universal calibration concept, was used to investigate the mechanism of extrusion-induced starch fragmentation in corn. High-amylose and high-amylopectin corn flours were subjected to twin-screw extrusion. The effects of moisture content, die temperature, screw speed, mass flow rate, and amylose-amylopectin ratio were investigated. Nonaqueous GPC, using a refractive index monitor and viscometer, yielded quantitative size profiles of native and extruded starches, as well as information describing branching patterns of the starch. Fragmentation was most pronounced in amylo-pectins with a molecular weight of 10(7)-10(9), which yielded fragments of 10(4)-10(7). Consistent with gravity-flow GPC with dimethyl sulfoxide, separation indicated that fragmentation was promoted at low temperatures. However, a correlation between degree of fragmentation and specific mechanical energy was not observed. Formulations containing high amylopectin levels were most prone to fragmentation. Die temperature significantly affected such textural properties as cohesiveness, springiness, gumminess, and chewiness of the extruded flours.