Effect of potato starch modification on mechanical parameters and granules morphology

Research was conducted to recognise the interrelations between morphology and mechanical properties of powders used in the food industry (dried potato protein, granulated starch, gelatinising starch, potato starch, pudding flour, starch thickener, and six kinds of dextrins: 40% white dextrin, 60% white dextrin, yellow dextrins: S, N, W, WB). Microscopic examination, determination of particle size distribution, particle shape index, as well as direct shear tests were performed. Single particles of dextrins were found to have similar shapes and dimensions. Classification of materials based on the results of mechanical testing was found to be in close agreement with classification based on morphology. The values of unconfined yield strength of dextrins and other materials investigated were found to be close, and characteristic of easy flowing and cohesive materials. Oscillations in the shear stress–strain curves were observed for two experimental materials: potato starch and white dextrin 60%, while those for other experimental materials run smooth. The highest values of unconfined yield strength σc were found in a range from 4.5 to 8 kPa for dried potato protein, at major consolidation stress values of 4 and 10 kPa, respectively. The lowest values of σc, characteristic for easy flowing and free flowing materials, were found for potato starch and granulated potato starch. The results of this study confirmed the relevance of morphology to the mechanical properties of powders.