| Automated gel permeation chromatography (GPC) with dimethylacetamide/lithium chloride, with application of the universal calibration concept, was used to investigate the mechanism of extrusion-induced corn and wheat starch fragmentation. The effects of extrusion operating conditions on starch structure and textural properties were studied. Detection of native and extruded starches using refractive index and viscosity detectors enabled application of Mark-Houwink calculations and quantitative size profiles to be obtained, as well as information describing branching patterns of the starch.; Corn starch fragmentation was most pronounced in amylopectins of MW 10{dollar}sp7{dollar}-10{dollar}sp9{dollar}, which yielded fragments of MW 10{dollar}sp4{dollar}-10{dollar}sp7{dollar}. Consistent with gravity-flow GPC in DMSO, fragmentation was promoted at low temperatures, however, a correlation between degree of fragmentation and specific mechanical energy was not observed. High amylopectin-containing formulations were most prone to fragmentation patterns. Die temperature was shown to significantly affect the textural properties of the extruded corn flours.; Wheat starch fragmentation was most pronounced in amylopectins of MW 10{dollar}sp7{dollar}-10{dollar}sp8{dollar}, which yielded fragments of MW 10{dollar}sp5{dollar}-10{dollar}sp7{dollar}. Of the operating parameters investigated, die temperature and moisture content led to extensive fragmentation. Methylation analysis showed only modest changes in linkage distributions, with little or no increase in terminal glucose indicating few fragmentation points relative to the total number of glycosidic linkages present. The lack of dextrins or oligosaccharides suggests that fragmentation occurs primarily in the B chains of amylopectin. Interactions between die temperature and moisture content were shown to significantly effect the textural properties of the extruded wheat flours. |
