干燥方式对桑葚粉热力学特性与贮藏稳定性影响  

Effects of drying methods on the thermodynamic properties and storage stability of mulberry powders

作　　者：王瑞颖 赵亚[1] 石启龙[1] 

机构地区：[1]山东理工大学农业工程与食品科学学院,山东淄博255000

出　　处：《食品与发酵工业》2018年第2期247-255,共9页Food and Fermentation Industries

基　　金：国家自然科学基金资助项目(31171708)

摘　　要：研究了喷雾干燥、冷冻干燥对桑葚粉吸附等温线与热力学性质的影响,探讨了2种干燥方式对桑葚粉玻璃化转变温度(glass transition temperature,T_g)与状态图的影响,比较了2种干燥方式所得桑葚粉的贮藏稳定性。结果表明,桑葚粉水分吸附等温线为Ⅲ型。Blahovec-Yanniotis为描述桑葚粉水分吸附特性的最适模型。桑葚粉的净等量吸附热与微分熵随含水率增加而降低并逐渐趋于恒定值;扩张压力随温度升高而降低,但随水分活度(water activity,aw)增加而升高;积分焓随含水率增加而降低并逐渐趋于恒定;但是积分熵随含水率增加先降低至最低值,而后升高并逐渐趋于恒定。桑葚粉水分吸附遵循熵焓互补理论,该过程为焓驱动、非自发过程。相同含水率/aw时,喷雾干燥桑葚粉的净等量吸附热、微分熵、积分熵高于冷冻干燥桑葚粉,但积分焓低于冷冻干燥桑葚粉。桑葚粉的T_g随含水率增加而降低,相同含水率时,冷冻干燥桑葚粉的T_g略高于喷雾干燥桑葚粉。25℃下,喷雾干燥与冷冻干燥桑葚粉的临界水分活度分别为0.095、0.115,临界含水率分别为0.076 1、0.079 2 g/g。The effects of spray drying and freeze drying on adsorption isotherms and thermodynamic properties of mulberry powders were investigated. The effects of two drying methods on glass transition temperature(T_g) and storage stability of mulberry powders were also compared and discussed. The results showed that the adsorption behaviors of mulberry powders followed type Ⅲ isotherms. Blahovec-Yanniotis model is the best fit to describe the absorption behaviors of mulberry powders. The net isosteric heating and differential entropy of mulberry powders decreased with moisture content increase,and then kept at the constant gradually. The spreading pressure of mulberry powders decreased with the increase of temperature,but increased with water activity(aw) increase. The integral enthalpy of mulberry powders decreased with increasing moisture content and remained at constant gradually. The integral entropy of mulberry powders decreased first(reached the minimum) and then increased rapidly with the increase of moisture content and then tended to be stable. The moisture adsorption of mulberry powders followed the enthalpy entropy complementary theory and the process was enthalpy driven and non spontaneous process. When the moisture content/awis at the same value,the net isosteric heat,differential entropy and entropy integral of spray-dried powders were higher than those of freeze-dried ones,but the integral enthalpy of spray-dried powders was lower than that of freeze-dried ones. The T_g of mulberry powders decreased with increasing moisture content. When the moisture content is the same,T_g of freeze-dried powders was higher than spray-dried ones. At 25 ℃,critical water activity of spray-dried and freeze-dried powders were 0. 095 2 and 0. 115 1,respectively. The critical moisture content of spray-dried and freezedried powders was 0. 076 1 g/g and 0. 079 2 g/g,respectively.

关 键 词：喷雾干燥 冷冻干燥 热力学性质 贮藏稳定性 

分 类 号：TS255.3[轻工技术与工程—农产品加工及贮藏工程]