RELATIONSHIP BETWEEN THE CONFORMATIONAL STRUCTURE AND PROCESSABILITY OF HYDROCOLLOIDS

摘要

Native starch and cellulose are semi-crystalline biohydrocolloids, by nature, structurally and functionally very weak for a diversified application in the (non-)food industry. Neither starch, nor cellulose can be processed easily by conventional thermoplastic processes, such as extrusion, injection moulding, kneading, casting or compression moulding, because both have to be disordered (i.e., gelatinized, melted or destructured) via high temperature, shearing and a suitable plasticizer. In case of starch, susceptibility to physical processing is determined by the ratio of amylose and amylopectin in the granular structure. High-amylose starch (long chain molecule) requires higher mechanical energy input than amylopectin (short-chain branched molecule) because of the high melt viscosity related to the higher gelatinization temperature and greater molecular entanglements, although the drawback is alleviated by better mechanical properties. An intrinsic analogy is given between amylose and cellulose, the latter enunciates its very high melting viscosity due to its highly ordered, chain-extended backbone, even though aided by the equatorial conformation of β-1,4-D-glucopyranose units.