摘要
为探讨干制菊花吸湿特性与其结构、水分活度(Aw)、贮藏温度的关系,本文以 2种菊花粉末(小黄菊和贡菊王)为对象,采用扫描电子显微镜(SEM)、傅里叶变换红外光谱(FT-IR)、X射线电子能谱(XPS)对其结构特征进行分析,结果显示菊花粉末表面粗糙,含有大量凹陷和孔洞;与小黄菊相比,贡菊王粉末粒径较小且表面含有更多的亲水基团,如-OH,O-C-O等.采用静态称量法在 20、30和 40℃和Aw=0.112～0.976下研究了2种菊花粉末的水分吸附行为,并通过模型拟合和热力学分析阐明了物料的水分吸附机制.菊花粉末的平衡干基含水率(Xe)随水分活度(Aw)增加而升高,但在同一Aw下,温度越高Xe值越低.Peleg模型是描述水分吸附等温线的最佳模型.热力学分析表明,净等量吸附热(qst)随平衡干基含水率升高而降低,其中小黄菊和贡菊王粉末的qst值分别于Xe＞0.14 g/g和Xe＞0.24 g/g时趋于恒定.小黄菊在 20、30和 40℃下的单分子层干基含水率(Xm)分别为 0.0690、0.0525、0.0505 g/g(干基),而贡菊王为 0.0645、0.0591和 0.0584 g/g(干基).有效孔径(rp)随温度和水分含量增加而增大,其中当Xe＞0.09 g/g(干基)时小黄菊粉末呈现介孔特性,而贡菊王粉末则当Xe＞0.11 g/g(干基)时内部孔隙才由微孔转变成介孔.研究结果可为菊花的干燥工艺优化与贮藏条件选择提供参考.
Abstract
To evaluate the correlation between the water absorption characteristics of dried chrysanthemums and their structure,water activity(Aw),and storage temperature,two types of powdered chrysanthemums("Xiaohuangju"and"Gongjuwang")were analyzed through SEM,FTIR,and XPS.The results indicated that the surface of the powdered chrysanthemums was rough and contained a large number of indentations and cavities.In comparison to"Xiaohuangju","Gongjuwang"powder had smaller particle sizes and more hydrophilic groups on the surface,such as-OH,O-C-O,etc.To examine the water adsorption behavior of two varieties of powdered chrysanthemums,the static gravimetric method was employed at 20,30,and 40℃and a range of Aw values from 0.112 to 0.976.Model fitting and thermodynamic analysis were conducted to gain insight into the water adsorption mechanism.An increase in water activity(Aw)resulted in a rise in the equilibrium water content(Xe)of powdered chrysanthemums,conversely,the higher the temperature,the lower the Xe values at the equivalent Aw levels.The fitting results demonstrated that the Peleg model was the most suitable model for depicting the water adsorption isotherms.Results from the thermodynamic analysis suggested that the net isosteric heat of adsorption(qst)decreased when the equilibrium water content(Xe)increased,and the qst values of"Xiaohuangju"and"Gongjuwang"powder remained steady in the presence of Xe values greater than 0.14 g/g and 0.24 g/g,respectively.The monolayer water content(Xm)of"Xiaohuangju"at 20,30,and 40℃were 0.0690,0.0525,and 0.0505 g/g(d.b),respectively,while those of"Gongjuwang"were 0.0645,0.0591 and 0.0584 g/g(d.b).When the temperature and water content increased,the effective pore size(rp)of"Xiaohuangju"powder increased,exhibiting mesoporous characteristics when Xe＞0.09 g/g(d.b).Conversely,the internal pores of"Gongjuwang"powder shifted from micropore to mesopore only when Xe＞0.11 g/g(d.b).The results of the study can be employed as a guide for improving the drying process of chrysanthemums and determining the most suitable storage conditions.
基金项目
安徽省自然科学基金项目(2008085MC103)
黄山市科技计划项目(2021KN-07)
安徽省高校自然基金重点项目(2023AH050135)
安徽省高校协同创新项目(GXXT2020-075)
维普
万方数据