基于水分迁移“态”变的红枣干制过程中质构特性形成机制研究

Jujube drying is usually accompanied by severe fruit compression and external tightening. At present, most of the researches are focused on the drying process and the change of quality, but the mechanism of water transfer and "state" is not clear. To Jun jujube as the material, in the hot air drying, microwave vacuum drying, freeze drying conditions of pulp water migration, free water, free water, combined with the effect of water on the structure and conformation of pulp fibers, reveal the moisture transfer and the "state" variation mechanism and moisture migration effect on texture. From the water evolution, molecular degradation of pectin by red dates texture changes, using low field NMR T2 relaxation, magnetic resonance imaging, atomic force microscopy, SPME / GC-MS techniques, physical and chemical state of the cell system of water level combination state, tissue distribution, moisture migration in the process of the environmental temperature and the influence on water migration, and establish the corresponding relationship between the main parameters and red dates sheet texture changes; at the same time, the research of pectin exonuclease and endonuclease, pectin pectinesterase, lead to changes in the main enzyme activity of endoglucanase and pectin pectin degradation process of different soluble pectin, pectin and carbohydrate. The relationship between dynamic analysis of pectin degradation and texture changes of rich red dates, red dates dry mechanism, provide the basis for the development of processing technology of red dates.

红枣干燥通常伴随着严重的果实内紧缩与外紧缩。目前研究多集中在干制工艺及品质变化方面，而水分迁移和“态”变的机制尚不清楚。以骏枣为材料，在热风干燥、微波真空干燥、冷冻干燥条件下，研究果肉中水分迁移、自由水、游离水、结合水对果肉结构与纤维束空间构象的影响，揭示水分迁移及“态”变机理及水分迁移对质构的影响。分别从水分演变、果胶大分子降解引起红枣质地变化出发，利用低场核磁共振的T2弛豫、核磁共振呈像、原子力显微,固相微萃取/气质联用等技术手段系统研究水分的物理化学状态、细胞水平结合状态、组织分布、干制过程中的迁移及环境温湿度对水分迁移的影响，并与红枣片质地变化的主要参数建立对应关系;同时研究果胶外切酶、果胶内切酶、果胶酯酶,葡聚糖内切酶等主要果胶酶活性变化导致的原果胶降解为不同溶解性果胶、果胶酸及糖类物质的过程，动态分析果胶降解与红枣质地变化的关系,为丰富红枣干制机理，开发红枣加工技术提供依据。

（1）通过对不同干燥方式所得产品的硬度进行测定分析，研究不同干燥方式对红枣品质特性的影响。硬度大小依次为微波真空干燥>热泵干燥>真空冷冻干燥；色泽无明显差异。产品的其脆度大小依次为真空冷冻干燥 > 真空微波真空干燥 > 热泵干燥。红枣片干燥后较干燥前硬度及咀嚼性显著增加，弹性及凝聚性无显著差异，真空真空冷冻干燥红枣片硬度最低，微波真空干燥硬度最大。.（2）采用扫描电镜技术，对红枣片干制期间微观结构变化情况进行了研究。不同干燥方式对枣内部细胞结构的影响也是不同的，自然风干、热泵干燥颗粒大，结构致密，感官表现为坚硬；由图可以看出，微波真空干燥在密闭环境中对红枣真空加热，内部出现多孔状网络结构，产品孔隙较大均匀一致，显示其呈现出较好的蜂窝状结构。.（3）采用低场核磁技术，对红枣片干制期间水分迁移情况进行了研究。表明微波真空干燥、热泵干燥有利于提高物料内水分的流动性，更有利于干燥的进行。干燥初期，自由水较易脱除。在干燥中后期，结合水和半结合水对应的信号幅值和横向弛豫时间逐渐开始减小。在同一时间段， 微波真空干燥、热泵干燥比真空冷冻干燥的 H +质子密度图像亮度低，说明微波真空干燥方式更易促进红枣片内部水分脱除。.（4）对红枣片热泵干制及微波真空干燥期间质构与水分进行了相关性分析。热泵干燥期间，红枣片中液泡水向细胞质水的转化在水分迁移过程中占主导地位。微波真空干燥时，液泡水的减少和细胞间质水的增加也是水分迁移的主要过程。