Physico-Chemical Behavior of Glycerol-Coated Cassava Starch Gels Incorporating Kaolin and Metakaolin

This study aims at analyzing the physico-chemical interactions in glycerol-coated cassava starch gels incorporating clay as mineral filler during heating. The physico-chemical and structural characterization of the clay used is composed of 75% kaolinite, 14% quartz and 11% illite. A thermal treatment at 700°C for 1 hour of this kaolinitic clay has allowed strong destructuring of the crystalline structure. The suspensions of glycerol plasticized cassava starch without charge or containing 5% by weight of clay were prepared and then heated at various temperatures between 30°C and 100°C. The suspensions viscosity increases according to the temperature up to a maximum following the penetration of the water molecules inside the starch grains. This phase is followed immediately by a sharp drop in the viscosity, resulting in a granular destructuring and solubilization of the starch grains. The suspensions incorporating metakaolin have a higher viscosity than those incorporating kaolin. The gels incorporating metakaolin have a hight ability to downgrade. The infrared spectroscopy of gels taken at different temperatures show the formation of the inter and intra molecular bonds within the starch granules.