重量法研究大豆水分吸附速率和有效扩散系数

Study on moisture adsorption rate and effective moisture diffusivity in soybean kernels by gravimetric method

在5种温度（10~35℃）、3个湿度（RH 65%、86%及100%）组合环境中,以称重法测定了初始低水分（4.33%~5.85%）、正常水分（11.74%~12.65%）、高水分（17.58%~17.89%）两个大豆品种“中黄37”和“澄豆”含水率随时间的变化,并采用修正的扩散方程描述水分吸附/解吸速率变化规律,对径向对称的球形大豆籽粒采用斜率方法分析计算水分扩散系数和活化能。在RH 65%~100%范围内,大豆初始水分越低,10~35℃条件的水分吸附速率越大,且温度较高,吸附速率较大。同样的初始水分条件,暴露的相对湿度越高,大豆的水分吸附/解吸速率越大。正常水分的大豆样品20~35℃水分吸附速率均在72 h内快速降低,而10℃水分吸附速率在96 h内缓慢降低。测定的两个大豆品种正常含水率样品10~35℃吸附过程中,水分有效扩散系数为1.920×10-8~5.253×10-8m2·h-1,活化能为10.711~23.358 k J·mol-1。对相同初始水分样品,随着温度增加,大豆籽粒水分扩散系数增加;随着相对湿度增加,籽粒活化能呈现增加趋势。随着进样初始水分增加,同一大豆品种籽粒水分扩散系数和活化能呈现增加趋势。

The soybean samples with low（ 4.33% ~ 5.85%）,normal（ 11.74% ~ 12.65%）,and high（ 17.58% ~ 17.89%）initial moisture content（ IMC） were used to determine the rate of moisture adsorption by gravimetric method at 10,20,25,30,35 ℃ under 65%,86% and 100% RH,respectively. A moisture diffusion equation was modified to fit for the relationship between moisture ratio of samples and exposed time. The soybean was considered as a sphere with radius symmetry,and its effective moisture diffusivity and activated energy was calculated using the method of slope.In the range of RH 65% to 100%,the lower the sample IMC,the higher moisture adsorption rate at temperatures of 10 to 35 ℃,and the moisture adsorption rate of samples were increased with an increase in temperature.Under the same IMC,the moisture sorption rate of samples were increased with an increase in exposed RH. For soybean samples with normal IMC,The moisture desorption rate at 20 to 35 ℃ were quickly deceased within 72 h under three kinds of RHs,but at 10 ℃,the moisture adsorption rate was slowly decreased within 96 h.During the sorption process of 10~35 ℃,the effective moisture diffusivity of two soybean varieties with normal moisture content ranged from 1.920 × 10- 8m2·h- 1to 5.253 × 10- 8m2·h- 1,the activated energy ranged from10.711 k J·mol- 1to 23.358 k J·mol- 1. For the samples with similar moisture,their effective moisture diffusivity were increased with an increase in temperature,their activated energy tended to be increased with an increase in relative humidity.For the same soybean variety,its effective moisture diffusivity and activated energy tended to be increased with the raise of initial moisture.