Determination of hydration rate for micro-konjac flour by rapid visco analyzer

The objective of this paper is to search for a rapid determination of hydration rate for micro-konjac flour. The hydration processes of konjac and micro-konjac flour were investigated by stereomicroscope and Rapid Visco Analyzer (RVA), respectively. The results showed that the hydration process of intact konjac granules could be viewed as swelling period and dissolving period. But these two periods could not be distinguished for micro-konjac flour because of its rapid hydration process almost completing in a minute. RVA could be used as a rapid test method to determine the hydration rate of micro-konjac flour. The suitable test concentration is 1%, test temperature, test speed, test time could be set as (30±1)℃, 160 r/min and 16 min, respectively. The results of curvilinear regression analysis showed that the viscosity data for hydration process of micro-konjac flour obtained by RVA were subjected to a model agreed with logistic procedure: η=η_max/(1+EXP(a-bτ)); τ is test time, η is the viscosity of the hydration process, η_{max is the attainable maximum viscosity, b is rate constant, a is a constant relating to initial viscosity. The rate constant (b) and the time reaching the half of maximum viscosity (τp=a/b) could be used as parameters of hydration rate for the hydration process. The difference of hydration rate between 120～140 mesh and 120～250 mesh of micro-konjac flour was successfully distinguished by application of these two parameters. The inhibition capability of sodium chloride solution for the hydration process of micro-konjac flour was also successfully distinguished by these two parameters for micro-konjac flour dispersed at different concentrations of sodium chloride solution. These results indicate that RVA is a very good fast technique for determining the hydration rate of mcro-konjac flour.}