Cassanelli Mattia, Prosapio Valentina, Norton Ian, Mills Thomas
School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT UK.
Food Bioproc Tech. 2019;12(2):313-324. doi: 10.1007/s11947-018-2210-6. Epub 2018 Nov 19.
The effect of three drying processes (freeze, oven and supercritical CO drying) on CP Kelco low-acyl gellan gum gel was investigated, highlighting the role of the water removal mechanism (i.e. sublimation, evaporation and solvent replacement/extraction) and the process parameters on the gel structure, rather than focusing on the drying kinetics. It is the first time that a research paper not only compares the drying methods but also discusses and investigates how the molecular and macroscopic levels of gellan gum are affected during drying. Specifically, the dried gel structures were characterised by bulk density and shrinkage analyses as well as scanning electron microscope (SEM) and micro-computed tomography (μCT) microscopy. Micro-differential scanning calorimetry (μDSC) was used in a novel way to investigate the effect of the drying technique on the polymer disorder chains by partial melting of the gel. The resulting water uptake during rehydration was influenced by the obtained dried structure and, therefore, by the employed drying process. It was found that freeze-dried (FD) structures had a fast rehydration rate, while both oven-dried (OD) and supercritical CO-dried (scCOD) structures were slower. After 30 min, FD samples achieved a normalised moisture content (NMC) around 0.83, whereas OD and scCOD samples around 0.33 and 0.19, respectively. In this context, depending on the role of the specific hydrocolloid in food (i.e. gelling agent, thickener, carrier), one particular dried-gel structure could be more appropriate than another. Graphical abstractFrom left to right: unprocessed hydrogels; μ-CT images of dried gels and unprocessed hydrogel; DSC curves after drying process.
研究了三种干燥工艺（冷冻、烘箱干燥和超临界CO₂干燥）对CP Kelco低酰基结冷胶凝胶的影响，重点突出了水分去除机制（即升华、蒸发和溶剂置换/萃取）以及工艺参数对凝胶结构的作用，而非聚焦于干燥动力学。这是首次有研究论文不仅比较了干燥方法，还探讨并研究了结冷胶在干燥过程中分子和宏观层面是如何受到影响的。具体而言，通过堆积密度和收缩率分析以及扫描电子显微镜（SEM）和显微计算机断层扫描（μCT）显微镜对干燥后的凝胶结构进行了表征。微差示扫描量热法（μDSC）以一种新颖的方式用于通过凝胶的部分熔化来研究干燥技术对聚合物无序链的影响。复水过程中产生的吸水量受所得干燥结构的影响，因此也受所采用干燥工艺的影响。结果发现，冷冻干燥（FD）结构的复水速率较快，而烘箱干燥（OD）和超临界CO₂干燥（scCOD）结构的复水速率较慢。30分钟后，FD样品的归一化水分含量（NMC）约为0.83，而OD和scCOD样品分别约为0.33和0.19。在这种情况下，根据特定水胶体在食品中的作用（即胶凝剂、增稠剂、载体），一种特定的干燥凝胶结构可能比另一种更合适。图形摘要从左至右：未处理的水凝胶；干燥凝胶和未处理水凝胶的μ-CT图像；干燥过程后的DSC曲线。
