Carboxymethylation of Plasticized Starch by Reactive Extrusion (REX) with High Reaction Efficiency

Carboxymethyl potato starches with degrees of substitution (DS) of 0.15–0.64 are synthesized in one step and in high levels of reaction efficiency (RE) using reactive extrusion processes on plasticized starch. The influence of process parameters such as screw geometry, specific mechanical energy (SME), temperature, and residence time on DS, RE and crystallinity are determined. SME have a surprisingly greater influence than the reaction time on RE. Up to 64% RE is reached with high values of SME (297 kJ kg−1). SME also have a major impact on starch chain degradation. The co‐rotating screw geometry have a positive influence on the RE. The temperature is found to have no effect on the reaction in the 90–120 °C range. Two types of malto‐dextrins are successfully used as alternative plasticizers for starch. The carboxymethylated starches are characterized using nuclear magnetic resonance spectroscopy, size exclusion chromatography, and X‐ray diffraction. This study shows that starch can be efficiently carboxymethylated in a plasticized medium with high RE using different plasticizers in very short reaction times. Carboxymethyl starch is synthesized by fast reactive extrusion process in glycerol plasticized medium. High specific mechanical energy (SME) provides high reaction yields in a very short reaction time. Substituent distribution patterns remain unchanged whatever SME parameters are used. Sugar dextrins can also plasticize the reaction medium.