Difference in sorption isotherms of different types of milled rice

The moisture sorption isotherm data of eleven milled rice varieties were determined by the static gravimetric method at five different temperatures (10, 20, 25, 30, 35℃) and relative humidity ranging from 11.3% to 96%.Modified Chung-Pfost (MCPE) was used to fit the sorption data.The fitted isotherms of adsorption, desorption, or the average of both were compared for different types of milled rice at each temperature.The fitted isotherms of adsorption, desorption, or the average of Japonica rice were respectively higher than those of Indica rice and glutinous rice.The difference in the adsorption isotherm between Japonica and glutinous rice was bigger than that of between Japonica and Indica rice.Both Indica rice and glutinous rice had the similar moisture sorption isotherms.Similar desorption isotherms were found between Japonica and Indica rice, but the significant difference in the desorption data between Japonica and glutinous rice was at low RH and a temperature of 10 ~ 30℃.The mixing and pasting behavior of rice flour dough was shown by Mixolab that the water absorption of Japonica rice flour was higher than those of both Indica rice and glutinous rice flours.The protein weakening (C2) of Japonica, Indica, and glutinous rice was in turn increased, but the starch gelatinization (C3) , physical breakdown of gelatinized starch granules (C4) and starch retrogradation (C5) were in turn decreased for Indica, Japonica, and glutinous rice.These results showed that the weak protein network and significantly low starch gelatinization of glutinous rice dough did not influence its water sorption when compared with Japonica and Indica rice dough.