Pressure-temperature phase diagrams of maize starches with different amylose contents.

The amylose/amylopectin ratio in starch granules has a distinct impact on the physicochemical properties of starches. In this study the effects of high pressure and temperature combinations on the gelatinization of four maize starches with different amylose contents were investigated in an excess of water (90% w/w). Microscopy was used to determine the loss of birefringence in starch granules. Experiments were undertaken in the pressure range of 0.1-750 MPa and temperature range of 30-110 degrees C, holding the conditions constant for 5 min. Temperature and pressure stabilities of high amylose starches were found to be significantly higher than those of waxy and normal maize starch. Thermodynamic models are proposed to describe the loss in birefringence as a function of pressure and temperature. From the pressure-temperature phase diagrams constructed it was evident that maize starch gelatinization is not accelerated at pressures below 300-400 MPa. However, at higher pressures the threshold temperature to initiate starch granule hydration and gelatinization is significantly reduced for all starches investigated. This study extends the knowledge of the impact of high pressure on food components and will possibly make the technology more attractive to use as a substitute for or in combination with conventional food-processing methods.