Microstructure and mechanical parameters of five types of starch
2006
Molenda, M., E-mail: [email protected] | Stasiak, M. | Horabik, J. (Polish Academy of Sciences, Lublin (Poland). Inst. of Agrophysics) | Fornal, J. | B³aszczak, W. | Ornowski, A. (Polish Academy of Sciences, Olsztyn (Poland). Inst. of Animal Reproduction and Food Research)
Microscopic examination, determination of particle size distribution, as well as direct shear and uniaxial compression testing were performed on five types of starch extracted out of: potato, wheat, corn, tapioca and amaranth. Regarding geometrical features (morphology) of granules, three distinct groups of materials were distinguished. Classification of materials based on the results of mechanical testing was found in a close agreement with classification based on morphology. Potato and wheat starches that had relatively large granules (d(0.5) of 41.5 and 20.2 mcm) and bimodal particle size distribution showed stress-strain curves with fluctuations, particularly high in the case of potato starch. Tapioca and corn starches had smaller granules of similar sizes (d(0.5) of 15.6 and 13.8 mcm, respectively). The uniaxial compression stress-strain curves of the two materials were also very similar, as well as their angles of internal friction. Granules of amaranth starch with d(0.5) of 3.0 mcm were several times smaller than those of corn and tapioca starches (parameter d(0.5) is the size in microns at which 50 percent of the sample is smaller and 50 percent is larger). As a result, amaranth starch was characterized by relatively weak compressibility and flowability, the lowest of all the materials tested
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