干燥过程中玉米籽粒水分扩散系数及热特性研究  

Effective moisture diffusivity and thermal property of shelled corn during drying

作　　者：姜平[1] 李兴军[1] 

机构地区：[1]国家粮食局科学研究院,北京100037

出　　处：《食品工业科技》2016年第15期53-59,65,共8页Science and Technology of Food Industry

基　　金：粮食公益性行业科技专项(201313001-03)

摘　　要：在45~75℃干燥箱中,分析了初始水分27.1%~34.5%的五个玉米品种含水率随时间的变化,并以修正的扩散方程(MPage)描述水分解吸速率,对平板状玉米粒采用斜率法计算水分扩散系数。MPage很好地拟合了干燥过程水分比率(MR)随时间的变化曲线(R^2>0.94,MRE<6.23%)。在75℃干燥,玉米解吸速率高达250×10^(-5)~350×10^(-5)min^(-1),在150 min内降低到最低;在45℃干燥,解吸速率则高达75×10^(-5)~100×10^(-5)min^(-1),在250 min内缓慢降低到最小值。在45~55℃干燥,龙江品种解吸速率曲线最低,郑单、先玉、唐抗、中糯四个品种的解吸速率曲线相似;在65~75℃干燥,唐抗品种解吸速率曲线最低,其他四个品种的解吸速率曲线相似。随着干燥温度的增加,玉米粒水分有效扩散系数增加;45~55℃水分有效扩散系数较接近,65~75℃水分有效扩散系数是45℃的2~3倍。龙江品种玉米在75℃干燥140 min和65℃干燥170 min,玉米裂纹破碎率明显增加。干燥温度和干燥时间不影响玉米的糊化温度起点、峰值、终点和峰值宽度,但是75℃干燥明显提高焓变和热流功率。The changes in moisture content of five shelled corn with initial moisture content 27.]%-34.5% were determined respectively at 45-75 ℃ in an electric heated blast oven, and a moisture diffusion equation（MPage） was modified to fit for the relationship between moisture ratio（MR） of samples and exposed time.A single corn kernel was considered geometrically to be a finite homogeneous slab shape, and its moisture diffusivity were given.The effective moisture diffusivity was calculated using a method of slope by plotting the experimental data in terms of In（MR）versus drying time. MPage fitted well for the i＇elationship between MR of samples and exposed time with R2〉0.94,and MRE 〈6.23%.The desorption rates of corn dried at 75 ℃ initially were 250 ×10^（-5）-350 × 10^（-5） min-1 ,and decreased to minimum within 150 min, but those dried at 45 ℃ initially were 75×10^（-5） - 100 × 10^（-5） min-1,and slowly decreased to minimum within 250 min.Among the five corn varieties, at drying temperature of 45 -55 ℃, cv.Longjiang had the minimum desorption rate, but other four varieties（Zhengdan,Xianyu,Tangkang, Zhongnuo） had the similar desorption rates.At drying temperature of 65-75 ℃, cv.Tangkang had the minimum desorption rate,but other four varieties had the similar desorption rates.The effective moisture diffusivity of corn increased with an increase in drying temperature.The effective moisture diffusivity of corn dried at 45-55 ℃ was approximate.The effective moisture diffusivity of corn dried at 65-75 ℃ was ]-2 times higher than that dried at 45 ℃. Fast green FCF dye showed that corn kernels of Longjiang variety were significantly broken during drying 140 min at 75 ℃, or 170 min at 65 ℃. Drying temperature and time had little effect on the onset（ To） , peak（ Tp）, conclusion（ Tc）temperature as well as temperature ranges （ Tc -To）of gelatinization, but the drying temperature ot 75 ℃ significantly increased gelatinization enthalpy and thermal power.

关 键 词：玉米 干燥 水分解吸速率 水分有效扩散系数 热特性 游离氨基酸 

分 类 号：TS255.1[轻工技术与工程—农产品加工及贮藏工程]