李果实冷藏期间风味劣变机制研究

Cold storage, one of the most effective methods, has been widely used for storing fruits and vegetables. However, chilling injury may occur during storage at a low temperature, which usually causes considerable losses of the commodities. Flavor deterioration is one of the typical chilling injury symptoms in many fruits including plum during cold storage. In order to reveal the mechanism of flavor deterioration in plum fruit during cold storage, and provide theoretical basis to improve flavor quality of plum fruit. This project plan to analyze and identify the contributions of volatile compounds in 'Angeleno' plum by headspace-solid phase microextraction combined with gas chromatography-mass spectrometry, and to track and clarify their changes by establishing the fingerprints of the volatile compounds during cold storage. In order to clarify flavor deterioration mechanism in plum from the molecular level during cold storage, cDNA sequences of four key synthases' gene in LOX pathway of plum are planned to be cloned, and the gene expression characteristics will be detected with real time fluorescent quantitative PCR technique. Changes of sweeteners and organic acids in plum during cold storage will be determined by a quantitive assay established with high performance liquid chromatography. Meanwile, to reveal the mechanism of flavor deterioration in plum fruit from the enzyme level, the related enzyme activity will be analyzed during cold storage. Application of this project will provide theoretical basis to understand the underlying flavor deterioration mechanisms, as well as practical ways to improve the flavor quality and market value of the plum fruit during cold storage.

冷藏是目前应用最广泛且行之有效的果蔬贮藏方法，风味劣变是李果实冷藏期间典型的低温伤害症状，也是其它冷敏性果实冷藏期间普遍存在的问题。为揭示李果实冷藏期间风味劣变机制，及有效调控冷敏性果实风味品质提供理论依据，本研究以'安哥诺李'为试材，采用气/质联用技术确定形成李果实嗅感风味的主要嗅感物质类型，通过色谱技术构建指纹图谱明确冷藏期间嗅感物质的变化规律；同时，克隆嗅感物质LOX途径四种关键合成酶基因的cDNA序列，采用实时荧光定量PCR技术研究李冷藏期间的基因表达特性，确定影响李嗅感风味的关键因素，从分子水平阐明李果冷藏期间嗅感风味劣变机制；通过色谱定量分析明确李果冷藏期间主要味感物质的变化规律，确定主要甜味物质含量与相关酶活的关系，从酶活层面阐明冷藏期间李果实味感风味劣变的主要原因；本研究旨在为生产者采取有效贮藏措施提高李果风味品质和市场价值提供理论依据，对促进李产业的发展具有重要意义。

风味劣变是李果实冷藏期间典型的低温伤害症状，也是其它冷敏性果实冷藏期间普遍存在的问题。为揭示李果实冷藏期间风味劣变机制，本研究以‘安哥诺李’为试材，采用气/质联用技术确定了形成李果实嗅感风味的主要嗅感物质类型，研究发现1-MCP处理和降低采收成熟度有利于李果实冷藏期间清香型物质的含量保持高水平，乙烯处理和成熟度低的果实冷藏后果香型物质含量降低。通过克隆嗅感物质LOX途径四种关键合成酶基因的cDNA序列，采用实时荧光定量PCR技术研究李冷藏期间的基因表达特性，研究发现1-MCP处理和成熟度高的李果实LOX基因的表达量在冷藏后期保持高水平，ADH和AAT基因的表达量明显处于低水平，这可能是其清香型物质含量低，果香型物质高的重要原因。成熟度低的李果实在冷藏前期LOX和HPL基因相对表达量低，冷藏后期的ADH、ATT基因相对表达量低，这可能是李果实的清香型物质含量高、果香型物质含量低的重要原因。利用HPLC分析了李果冷藏期间主要味感物质的变化，结果发现乙烯处理处理和高成熟度的李果冷藏期间保持了较低的可溶性糖含量，同时冷藏期间淀粉酶，蔗糖酸性转化酶、蔗糖中性转化酶保持了较高的活性，这可能是冷藏期间的可溶性糖含量较低的重要原因。降低李果的采收成熟度和乙烯处理使保持李果冷藏期间保持较高的有机酸含量；乙烯处理抑制了李果冷藏期间NADP-ME和NAD-ME酶活性，提高了PEPC、CS、ACO、MDH的活性，这可能是其保持高的有机酸含量的重要原因。此外，利用近红外光谱技术实现了对李果实成熟度无损鉴别，为提高实验结果的准确性提供了技术保障。本研究为有效调控冷藏李果实的风味品质奠定了理论基础，对促进李产业的发展具有重要意义。