Derivatization of Starch Granules as Influenced by the Presence of Channels and Reaction Conditions

摘要

Research related to (a) effects of the presence of channels, (b) the natures of derivatizing reagents, and (c) the nature of the reaction medium and reaction conditions on the efficiency and location of derivatizing reactions in starch granules is reviewed. The presence of channels in starch granules influences the path of reagent solution penetration into granules. In granules in which channels are present, reagent solution largely passes through the channels to the interior cavity and then penetrates the granule matrix from the cavity outward, but granules are heterogeneous, both with respect to channelization and with respect to patterns of reagent solution penetration. Development of two methods to determine locations of reaction within granules is reviewed. Both methods revealed that phosphoryl chloride, a highly reactive reagent, reacts primarily on or near granule surfaces (the external surface of potato starch granules which have no channels, and all surfaces [predominately the surfaces of channels and the cavity, but also to a lesser extent the external surface] in corn starch granules). On the other hand, an analog of propylene oxide, a slowly reacting reagent, was able to diffuse throughout granules before reacting, resulting in more uniform, but not completely homogeneous, derivatization. Factors effecting efficiency of the modification of waxy corn starch with propylene oxide and a derivative of it are reviewed. pH is the predominate variable. This data reinforced the previous conclusion that there is a correlation between swelling and reaction efficiency, with greater swelling resulting in greater efficiency. The research reviewed is practically important as one route to the production of improved modified starch products, especially modified food starches, within restrictions of types of reagents and degrees of modification that can be used.