Starch gelatinization corresponds to a melting phase transition in aqueous medium. Such a transition involves important mass transfer of water. Using a high-pressure bomb including optical ports, the volume variation of starch granules in suspension was related to gelatinization during a high-pressure treatment up to 420 MPa. Microscopic observations of wheat and potato starch granules were compared with macroscopic measurements of compressibility up to 600 MPa and gelatinization intensity using differential scanning calorimetry on treated suspensions. Wheat starch gelatinization started below 300 MPa and was completely achieved at 600 MPa. Potato starch was not altered under 600 MPa. The behavior of the volume variation of starch granules under pressure compared with starch suspensions compressibility could be explained by simultaneous compression and hydration mechanisms. Keywords: Starch gelatinization; high hydrostatic pressure; image analysis

Wheat starch suspensions of 5% dry matter were treated at 86 °C, 15 min, or with pressure at 600 MPa, 25 °C, 15 min. Both treatments were found to induce no further melting peak when differential scanning calorimetry was used. Under these previous conditions, starch suspensions subjected to pressure gave original products in terms of swelling index (water binding), amylose release and specific gravity. Pressure induced starch gelatinization with preservation of the granular structure. As a consequence, peculiar properties were expected for pressure-induced gels of 30% dry matter obtained at 600 MPa, 25 °C, 15 min. By using Young modulus measurements, calorimetry, X-ray diffraction, and drying kinetics experiments, results showed a limited retrogradation for gels obtained under pressure. Keywords: Starch gelatinization; gel; high pressure; specific gravity; retrogradation

Wheat starch suspensions in water (5% dry matter) were subjected to various pressures (0.1-600 MPa) and temperatures (-20 to 96 degrees C) for 15 min. The gelatinization rate was measured after treatment by using microscopic measurements of the loss of birefringence of the granules. This method was previously calibrated by differential scanning calorimetry. Curves of isogelatinization were found to be quite similar to a pressure-temperature (P-T) diagram of unfolding proteins. Results were first analyzed by considering the thermodynamic aspects related to the dT/dP curve shifts. On the basis of equations already shown for proteins, the P-T gelatinization diagram of wheat starch would show different kinds of thermal contributions, suggesting endothermic, athermic, or exothermic melting reactions. Second, as a practical consequence, these previous P-T areas corresponded to specific gelatinization conditions as confirmed by hydration evaluation measured by starch swelling index. Depending on the pressure-temperature conditions, gelatinization would involve hydration. Lowering the pressure and temperature resulted in a complete gelatinization with less hydration in comparison with a thermal treatment at atmospheric pressure. A hydration model based on an energetic approach was proposed.

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