不同类型大米吸着等温线差异性研究
Difference in sorption isotherms of different types of milled rice
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摘要: 对11个大米样品(5个粳米、2个籼米、4个糯米),采用静态称重法测定了水分吸附和解吸等温线数据,温度分别为10、20、25、30、35℃,相对湿度范围11.3%96%,并分别采用修正Chung-Pfost方程(MCPE)拟合等温线。在1035℃范围内,拟合的粳米、籼米及糯米每个温度水分吸着等温线依次降低。粳米与糯米之间吸附等温线差异显著大于粳米与籼米之间吸附等温线差异,籼米与糯米之间吸湿性相似,粳米与籼米解吸等温线之间差异不显著,但是粳米与糯米解吸等温线之间在1030℃范围、低相对湿度下存在差异。Mixolab分析仪适量加水实验显示,粳米米粉的吸水率大于籼米和糯米。粳米、籼米、糯米米粉团的蛋白质网络强度(C2)依次减少,但是米粉团淀粉糊化(C3)、糊化淀粉粒的物理溃败(C4)和淀粉回生(C5)减少次序是籼米、粳米和糯米。与籼米比较,糯米米粉团具有弱的蛋白网络、低的淀粉糊化粘度值、低的糊化淀粉粒物理溃败和淀粉回生值,这些物理化学特性不降低其米粉吸水率。Abstract: 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.