Starch fragmentation in relation to processing conditions and sensory quality of conventional processed grit corn flakes
Abstract
A study is presented on the influence of processing conditions on tempering grit rheology and the resulting molecular fragmentation of starch that occurs during the milling of conventional processed grit corn flakes. Corn grits were tempered and milled under a range of combinations of processing conditions which included low and high percent moistures and tempering temperatures. Starch fragmentation was determined using hot and cold water-soluble fractionation methods and an intermediate-pressure size-exclusion chromatograph with multi-angle laser light scattering and refractive index detection. Rheology of the tempered grits was obtained using a broad band frequency squeezing flow technique. Results showed that tempered grit moisture content and tempering temperature and time directly influence the rheology of the tempered corn grits. Rheology of the tempered corn grits was shown to directly influence mill gap width and roll vibrations. Corn grits processed under low moisture-low tempering temperatures were significantly harder. Generally, moisture content was the principal component governing final grit hardness and milled flake thickness in experiments using the same flaking roll setting. Processing conditions resulting in increased shear forces at the flaking mill produced increased amounts of fragmented amylopectin with decreasing average molecular weights. Overall, thinner flakes produced a higher degree of starch fragmentation, yet processing conditions can be modified to yield a range of starch fragmentation for any given milled flake thickness. Characterization of the fragmented starch occurring during milling is presented. Depending on processing conditions, the average molecular weight of the branched polymer was 1.5 × 10 6 to 1.1 × 107 Da. Resulting starch fragmentation was shown to strongly impact bowl life and overall sensory quality of the finished corn flakes. Corn flake samples containing high amounts of starch fragmentation were positively correlated to increased water uptake and increased leaching of starch fragments into water. Processing conditions resulting in corn flakes of the same milled flake thickness, but containing different amounts of starch fragmentation, further corresponded to different bowl lives with the flake sample containing the highest amount of starch fragmentation yielding the poorest bowl life.
Degree
Ph.D.
Advisors
Hamaker, Purdue University.
Subject Area
Food science
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