基于微波真空干燥技术的苹果脱水行为与品质调控研究

There is a prominent contradiction that a loss rate up to 25% and a 20%-33% processing rate of apple postharvest in China occurred while the apple crop production was booming and its yield had a rapid rise. So it is necessary to decrease the loss of apple postharvest and add its value by apple intensive processing, which will contribute to the healthy and sustainable development of the apple production. Currently, most of the studies on microwave vacuum drying technology (MVD) focus on modeling drying kinetics and evaluating energy efficacy. It is necessary for MVD extensive application in food processing to understand the process and quality control method in special MVD product. In this project, the high-efficacy MVD) is applied to dehydration process of China's big fruit, apple. Specifically, we will systematically study the effect of dehydration conditions including Apple varieties, cutting, blanching and/or various osmotic treatment on the MVD dehydration process and the quality of the apple, quantificationally analyze and model the dehydration process and the quality development law; furthermore, the role of these factors in the structure and quality development of MVD products will be discussed using both instrument and sensory evaluation. The results of the research will provide both a theoretical basis and a practical introduction to producing the apple crispy slices (cubes) of high-quality.

与我国苹果种植业的蓬勃发展和产量的迅猛增长形成鲜明对比的是采后高达25%的损失率和20%-33%的低加工率，因此，对其进行深加工以减少采后损失、提高附加值对于苹果产业的健康可持续发展意义重大；目前，有关食品微波真空干燥（MVD）的研究主要集中于干燥动力学与能效的研究，要使高效的MVD广泛的应用于食品加工，必需结合特定原料与期望的产品属性进行深入研究。本项目将MVD应用于我国大宗水果-苹果的脱水加工，系统研究了苹果种类、切分程度与热烫和/或不同渗透剂渗透处理对苹果MVD脱水过程与品质的影响，定量模拟分析其脱水过程与品质形成规律；采用客观仪器分析与主观感官评估相结合的方法，分析和探讨了这些因素在产品结构与相关品质形成中的作用，以期为高品质苹果脆片（粒）的高效脱水生产提供理论依据与现实指导。

本项目将微波真空干燥（MVD）技术应用于我国大宗水果-苹果的脱水加工，系统研究了苹果种类、切分程度与热烫和/或不同渗透剂渗透处理对苹果MVD 脱水过程与品质的影响，分析和探讨了这些因素在产品结构与相关品质形成中的作用；结果表明，由于显著的焦化效应，单独的MVD仅适合于脱水苹果(水分含量20%)的加工，热风预干燥与MVD结合适合于苹果脆片（水分含量低于7%）的加工,受干燥方法影响的样品的干缩率在23.3-85.7%之间，热烫且热风干燥所得脱水苹果片干缩率最大，热风预干燥与MVD组合干燥苹果片干缩率最小；切片形状与尺寸对MVD特性有显著影响，切片厚度越大干燥速率越大，所需的干燥时间越短，5种不同预处理的水分扩散系数由小到大依次为：热烫+糖渗透、超声、蒸汽热烫、糖渗透、硫处理，水分扩散系数由1.64×10-8m2/s增加到3.46×10-8m2/s;热烫和渗透组合处理可以改进干燥速率与脱水以及膨化产品品质，其中低聚果糖渗透处理的样品干燥膨化后感官品质最好，微结构观察表明形成空大壁厚的蜂窝状结构；比较了不同种类苹果产品的物理与化学特征与感官图谱,苹果脆片的玻璃化转变温度(Tg)和比焓值分别在105.66-161.42℃和5.03-80.37 J/g之间并受热烫方式、苹果品种、糖液浓度和种类的影响；低场核磁共振和介电特性分析结果表明预处理改变了膨化前样品的水分结构、组成与微波吸收特性进而在不同程度上影响苹果的膨化与相关品质; 本项目获得了通过干燥前处理技术调控微波真空干燥苹果产品的工艺途径，对苹果加工具有重要现实指导意义。