| In this paper, two kinds of unhusked rices “gangyou 527” and “jianjiannuo” and their brown rices were used as experimental samples. The change rules of adsorption and desorption of the unhusked rice and brown rice with different initial moisture contents at different temperatures(10, 20, 25, 30 and 35℃) and different relative humidities(RH65%, RH86% and RH100%) was determined, and the relationship between moisture contents of the unhusked rice and brown rice and their glass-transition temperatures was also determined. At the same time, the unhusked rices “zhongjiazao” and “zhunliangyou” were used as experimental samples, and the change of moisture contents of the unhusked rice, cracking rate and breakage rate during drying process was further determined. The results showed as follows:(1) The moisture contents of unhusked rices and brown rices increased or decreased fast at the beginning(<48h) of adsorption/desorption with the increasing treatment time, and the adsorption/desorption rate was higher, then, the adsorption/ desorption rate became lower gradually. At the same temperature, the higher the relative humidity, the higher the rate of moisture absorption. At the same relative humidity, the higher the temperature, the higher the rate of moisture absorption, and the shorter the time of reaching equilibrium moisture. During adsorption process of unhusked rice and brown rice, the lower the initial moisture content, the higher the rate of moisture absorption. When moisture was high during desorption process, the higher the relative humidity, the lower the rate of moisture desorption.(2) The relationship of MR-t of two unhusked rice and their brown rice was matched with six moisture diffusion equation of Lewis, Wang-singh, Page, modificatory Mpage1, Mpage2 and Mpage3, among them Mpage3 was best, residual sum of squares, standard error were the least, and the determination coefficient was the largest. In the range of 10℃ to 35℃, the higher the relative humidity, the lower the moisture diffusion coefficient k value.(3) During the beginning within 48 h, moisture ratio curve decreased fast with increasing time, gradually flattened out and closed to zero after 48 h. The higher the temperature, the faster the moisture ratio curve decreased. With the increase of relative humidity, the trend of moisture ratio curve flattened out gradually, and time to reach zero was longer, that was consistent with the change rule that the higher the relative humidity, the lower the moisture diffusion coefficient k value.(4) with the increasing moisture contents of unhusked rice and brown rice increased, the glass-transition temperature decreased, the range of the glass-transition temperature was about 30℃ to 55℃. The higher the moisture content of unhusked rice and brown rice, the lower the ultimate temperature was allowed to be heated. Within the normal range of moisture content of unhusked rice and brown rice, the glass-transition temperature of brown rice was a little higher than unhusked rice’s.(5) within the drying temperature range of 45℃ to 65 ℃,the moisture contents of unhusked rice “zhongjiazao” and “zhunliangyou” gradually decreased with the increasing dry time, especially at 65℃. The higher the drying temperature, the shorter the time of high moisture content to moisture content of safe storage. The number of cracking kernels of husked rice increased with the increasing drying time and the increasing drying temperature,the number of crack also increased, especially in three crack area. The different varieties of unhusked rice had different degree of cracking. With the increasing drying time, the value of absorbance of fast green FCF of husked rice gradually increased. When dried at higher temperature, the broken kernels of brown rice increased with the increasing drying time during processing the unhusked rice, the number of dying kernels also increased, and the dying area of broken kernels enlarged. However, no obviously difference was observed between the two varieties. |
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