玻璃化冷冻对蓝莓冻融损伤的机理研究

Blueberry is a kind of small berry fruit with rich nutrition, unique taste and high economic value. However, fresh blueberries have short shelf life and easy to rot because of dehydration. Although refrigeration technology can maintain the original quality of blueberries to some extent, but it is very difficult to overcome the freeze-thaw damage to blueberries by vitrification freezing because of the presence of ice crystals. In order to study the effect of ice crystals on freezing and thawing, reveal the mechanism of quality breakdown in freeze-thaw process, Dandong high bush blueberry will be chosen as materials in this proposal to track the process of blueberries frozen water, ice crystal size and shape changes using low field nuclear magnetic resonance (LF-NMR) imaging technology, and establish of spin - spin relaxation time T2 relationship with the ice structure of the model to deeply study the effect of water migration on the formation of ice crystals. This proposal will also identify the texture damage of vitrification to blueberries by measuring pectin content, membrane permeability and freedom droplet values to prove the membrane integrity. To study the effect of vitrification process on the content of blueberry fruit quality and the interactions between the components to reveal the mechanisms of quality changing based on the rule of the ingredient including sugar, Vc, polyphenols, volatile compounds, color and anthocyanins after freezing-thawing. Excepted results will provide a scientific basis for reducing the damage of blueberry freeze-thaw and a reference for optimization of the freezing process.

蓝莓是一种营养丰富、口感独特、具有较高经济价值的小浆果类水果，但鲜食蓝莓货架期短、容易失水腐烂，冷冻技术可以在一定程度上保持蓝莓的原有品质，由于冰晶的存在，玻璃化冷冻也难以克服冻融对蓝莓的损伤。为寻找冰晶体对蓝莓冻融的影响，揭示冻融过程中蓝莓品质劣变的机理。本课题拟以辽宁丹东高丛蓝莓为主要对象，采用低场核磁共振成像技术跟踪冷冻过程蓝莓水分、冰晶大小和形状的变化，建立自旋-自旋弛豫时间T2与冰晶结构特征关系模型，深入研究冷冻过程中水分迁移对冰晶体形成过程的影响；通过测定果胶含量、细胞膜渗透性和解冻后自由液滴值表征细胞膜完整性，明确玻璃化冷冻对蓝莓质构的损伤；针对蓝莓在冻融后糖类、Vc、多酚、风味、色泽和花青素等成分的变化规律，探究玻璃化冷冻过程对蓝莓品质组分的影响及组分之间的相互作用，揭示蓝莓冷冻过程品质变化机理。本研究可为降低蓝莓冻融损伤提供科学依据，为其冷冻工艺优化提供参考。

本项目针对鲜食蓝莓货架期短、容易失水腐烂，冷冻技术可以在一定程度上保持蓝莓的原有品质，重点研究玻璃化冷冻过程中蓝莓水分迁移、质构劣变及营养风味物质的变化。以高丛蓝莓为试验材料，常规冰箱冷冻为对照，分别以深度冰箱和液氮两种玻璃化冷冻方式进行处理，采用低场核磁共振成像技术跟踪蓝莓冻融过程中水分分布和迁移情况，通过化学分析和仪器测试相结合测定冻融过程中质地、果胶物质、营养成分及风味物质的含量变化，揭示玻璃化冷冻对蓝莓冻融损伤机理。结果表明，通过-80 ℃超低温冰箱冷冻处理的蓝莓T23弛豫时间值明显高于其他冻融处理( p < 0.05)，最接近新鲜样品。无论何种冷冻方式，冻融后的蓝莓质地参数都显著区别于新鲜蓝莓。液氮玻璃化处理组的滴水损失较严重，部分发生了冻裂现象，整个贮藏阶段，各处理组之间的可滴定酸含量无显著差异（p ﹥0.05），在冻藏末期，蓝莓果肉褐变程度呈现增加趋势，常规冰箱冻藏的蓝莓褐变较为严重，整个果实大部分都呈现红化现象，虽然液氮冷冻蓝莓果肉褐变程度较小，但是从其外表皮上可以看到明显的裂痕，并有一些汁液溢出，这说明液氮不适合蓝莓冻结。通过对电子鼻雷达图主成分分析（PCA）、传感器贡献率分析（LA）、线性判别分析（LDA）和GC-MS分析表明非玻璃化冻藏蓝莓在贮藏结束时香气物质变化较为明显，经液氮冷冻并冻藏的蓝莓在贮藏期间香气成分变化较小，风味较为稳定。总体来说，相比普通冷冻和冻藏处理，玻璃化冷冻和冻藏能较好保持蓝莓品质特性。本研究可为降低蓝莓冻融损伤提供科学依据，为其冷冻工艺优化提供参考。