果蔬热加工风味劣变严重影响产品品质，解析其异味形成机理是该领域研究热点。甜瓜是极热敏性水果的典型代表，申请人前期研究确定DMS, DMTS和3-甲硫基-丙醛是其热加工异味形成的关键组分。本课题通过对热加工香气劣变的甜瓜汁体系进行模拟，并通过组分省略实验，进一步验证三种含硫化合物对异味形成的贡献；利用离子交换树脂分离、反相色谱、离子排斥色谱等技术对异味前体物质进行提取、分离和纯化；利用飞行时间质谱进行高分辨率液质联用检测，结合核磁共振和稳定同位素稀释分析，对异味形成的中间体和前体物质进行定性、定量，并提出异味形成的反应网络；最后通过在模拟体系中分别添加methyl-d3标记的前体物质，定性鉴定加热后其转移变化，并定量研究含硫化合物、中间体和前体物质的变化，对形成的分子机制进行验证。研究结果为果蔬热加工异味形成分子机制的科学阐述提供借鉴，更为加工中有效阻断或降低香气劣变措施的制定提供理论依据。

Off-flavor generated during thermal processing of fruits and vegetables could seriously deteriorate product quality, making study on off-flavor generation mechanism becomes the research focus. Muskmelons are typical representative of thermo-sensitive fruits. Our previous study revealed that three sulfur volatiles namely DMS, DMTS, and methional are major off-note contributors in thermally-processed muskmelon juice. In this project, firstly, recombination experiment and omission test will be used to confirm and evaluate the contribution of three sulfurcompounds and then their possible off-flavor precursors (OP) will be extracted, isolated and purified by applying several chromatogram techniques such as ion-exchange chromatogram, inverse-phase chromatogram, ion-exclusion chromatogram and then to be qualified accurately using TOF-MS, HR-HPLC-MS. Based on qualification and quantification of intermediate products and precursors using NMR and SIDA, thermal degradation pathways of the OP to generate the three major volatile sulfur off flavors will be proposed and finallyproposed generation pathways of thermally-processedoff-notes will be verified using specific isotope addition method (methyl-d3isotopes) by analyzing the transformation ofmethyl-d3 and changes of the sulfur off-notes, intermediates and the precursors after thermal processing. This study will guide the other related study aiming to reveal the off-note generation mechanisms and will promote the establishment of possible prevention solutions to thermally-generated off-notes.