New insight in crosslinking degree determination for crosslinked starch.

The crosslinked starch has been studied for many years, but it is difficult to characterize degree of substitution on crosslinking of the very high and low crosslinked starches. The available approaches (including viscosity, settling volume, and P content) all have their limitations, i.e., not applicable in a large scope, pollution problem, and can not reflect the internal structure change. Here in this paper starch-iodine (St-I) method was proposed as a new approach to characterize the crosslinking degree. In this investigation, three starches of A, B, and C crystalline pattern with different amount (from very low to very high, 0.01, 0.05, 0.1, 0.5, 1, 5, 10%) of crosslinking reagent added were studied. This method is based on the mechanism that crosslinking reaction take place between amylose/amylopectin, amylopectin/amylopectin, whereas the amylose dose not crosslink one another. After crosslinked to amylopectin, the result amylose-amylopectin complex can be considered as a new amylopectin. Results showed that the St-I method can characterize all the crosslinked starches of the three starches, at low reagent level (0.01-0.1%), the amylose was found to decrease rapidly, this can also replace the viscosity method, whereas at high reagent level (1-10%), although the significant differences can still be observed, the effect was not so obvious as it for the lower crosslinked starches, here we firstly applied dose efficiency to characterize this phenomenon, which was informative and helpful in determining this modification process.