Zhao Xuewei, Wei Xiaoxiao, Wang Hongwei, Liu Xingli, Zhang Yanyan, Zhang Hua
College of Food and Bioengineering, Zhengzhou University of Light Industry, Zhengzhou 450001, China.
Henan Key Laboratory of Cold Chain Food Quality and Safety Control, Zhengzhou 450001, China.
Foods. 2023 Mar 30;12(7):1470. doi: 10.3390/foods12071470.
Water diffusivity, a critical parameter for cereal processing design and quality optimization, is usually concentration-dependent. dynamic vapor sorption (DVS) system provides an approach to establishing the relationship between water concentration and diffusivity. However, the usual relative humidity (RH) jump during practical sorption processes is usually greater than that adopted in DVS measurements. Water vapor sorption kinetics of glutinous rice grains, glutinous rice flour and wheat flour dough films were measured using the DVS system to verify if varying RH step sizes can obtain identical diffusivities within the same range. The effective diffusivities were determined according to Fick's second law. The results revealed that increasing RH step size led to a higher estimated diffusivity, regardless of whether the water concentration gradient or potential chemical gradient was considered a driving force for water diffusion. This finding was further confirmed by a linear RH scanning DVS measurement. The water concentration-dependent diffusivity obtained from a multi-step DVS measurement, according to Fick's second law, will overestimate the required time for practical cereal drying or adsorption. Thus, this paradoxical discrepancy needs a new mass transfer mechanism to be explained.
水分扩散率是谷物加工设计和品质优化的关键参数，通常与浓度相关。动态蒸汽吸附（DVS）系统提供了一种建立水分浓度与扩散率之间关系的方法。然而，实际吸附过程中常见的相对湿度（RH）跃变通常大于DVS测量中采用的跃变。使用DVS系统测量了糯米颗粒、糯米粉和小麦粉面团薄膜的水蒸气吸附动力学，以验证不同的RH步长是否能在同一范围内获得相同的扩散率。有效扩散率根据菲克第二定律确定。结果表明，无论将水分浓度梯度还是潜在的化学梯度视为水分扩散的驱动力，增加RH步长都会导致更高的估计扩散率。线性RH扫描DVS测量进一步证实了这一发现。根据菲克第二定律，从多步DVS测量获得的与水分浓度相关的扩散率将高估实际谷物干燥或吸附所需的时间。因此，这种矛盾的差异需要一种新的传质机制来解释。
