天然多酚对热加工甜瓜汁中“发酵”异味的抑制作用及其分子机制

Muskmelons are typical thermo-sensitive fruits and could produce obvious “fermented” off-flavor during thermal processing, seriously restricting its industry development. Therefore, the study on solutions to the “off-flavor” problem has become a main focus and hotspot in muskmelon favor research. In our previous study, seven compounds that could contribute to the “fermented” off-flavor were screened and all of them were revealed to be Maillard reaction (MR) products. Besides, many literatures demonstrated that natural polyphenols, which are represented by catechins, could effectively inhibit the Millard reaction, and thus significantly reduce the related off-flavor compounds production. On these basis, a hypothesis that natural polyphenols could also effectively inhibit the generation of Maillard-type “fermented” off-flavor in heated muskmelon juice was proposed in this project. Based on previous verification of natural polyphenols’ effectiveness in inhibiting the “fermented” off-flavor by triangle test, this study will further mainly focus on demonstrating the regularity of inhibiting effect of polyphenols on the formation of “fermented” off-flavor in heated muskmelon juice, and revealing the off-flavor inhibiting molecular mechanism of natural polyphenols. Firstly, the target compounds responsible for the “fermented” off-flavor will be revealed at molecular level by using sensomics technologies including gas chromatography-high resolution mass spectrometry (GC-HRMS) and recombination model experiment. Furthermore, the effectiveness of natural polyphenols on inhibiting the formation of fermented off-flavor will be comprehensively evaluated on both sensory and chemical scale by using adding experiment, triangle test and stable isotope dilution analysis (SIDA). Finally, adding experiments of natural polyphenols with different structures combined with odor activity value calculation and seven-point scale sensory evaluation analysis will be carried out to clarify the molecular mechanism of inhibitory effect of polyphenols on formation of “fermented” off-flavor through systematically studying the structure and fermented off-flavor-inhibiting activity relationship, analyzing the causes of activity differences and defining the pathway by which polyphenols alter MR pathways. This study will guide the promotion of deep processing technologies of muskmelon juice and will also provide references for the industry development of other thermal-sensitive fruits.

甜瓜是典型热敏性水果，热加工中“发酵”异味明显，严重制约产业发展，攻克异味问题是该领域研究热点。申请人前期鉴定出七种“发酵”异味组分且均为美拉德反应产物；大量文献证实：儿茶素为代表的天然多酚能抑制热加工食品中的美拉德反应，有效减少异味。基于此，本项目提出假说：天然多酚能抑制热加工甜瓜汁的发酵异味，在前期初步验证多酚有效性基础上，重点聚焦多酚抑制“发酵”异味的作用规律和分子机制。首先采用色谱-高分辨质谱联用和体系重组等感官组学技术，从分子水平明确发酵异味靶向分子；通过添加实验，利用三点法和同位素稀释精确定量，从感官、分子双维度评价多酚“发酵”异味抑制效果；通过不同结构多酚添加实验，利用香气活性值和七点强度法，研究多酚抑制作用构-效关系，解析构-效差异原因、明确具体作用类型，最终阐明多酚抑制“发酵”异味分子机制。研究能为甜瓜深加工技术提升提供理论依据，更能为其它热敏性果品产业发展提供重要借鉴。

本项目以“热加工甜瓜汁的发酵异味问题”作为切入点，在申请人前期研究发现“七种发酵异味贡献组分均为美拉德反应产物”和大量文献证实“多酚能够明显抑制美拉德反应，减少异味生成，有效解决热加工食品体系中异味现象”的基础上，提出“多酚物质同样能够抑制热加工甜瓜汁中的发酵异味”这一大胆假设，重点聚焦“发酵异味的化学本质”、“多酚对发酵异味的抑制作用规律”、“多酚抑制效果的构-效关系”三部分研究内容，在明确揭示热加工甜瓜汁发酵异味的靶向分子的基础上，从分子和感官双维度准确系统评价多酚在热加工甜瓜汁发酵异味生成中的抑制效果、表征抑制效果-浓度关系，解析构-效关系差异原因，明确具体抑制作用类型，最终阐明多酚抑制热加工甜瓜汁“发酵”异味的分子作用机制。..热处理后甜瓜汁中关键香气贡献组分构成发生了根本变化，不同甜瓜品种的热异味组分构成具有普遍规律，具有较高稀释因子硫醚和小分子醛酮物质是关键异味贡献物质，其中二甲基硫醚是最重要的异味贡献组分；四种strecker醛类及两种杂环化合物是“发酵异味”的主要来源，其中乙醛为最重要的“发酵异味”贡献组分。..不同多酚对异味的抑制效果研究表明，感官评价和仪器分析结果相一致，均表明相同浓度儿茶素、染料木黄酮、黄豆苷元、海藻多酚处理对热处理甜瓜汁的异味生成均有不同程度的抑制作用；其中儿茶素的抑制效果最佳，其次是海藻多酚，黄豆苷元，染料木黄酮；与儿茶素相比，染料木素和黄豆苷元的抑制效果都有所降低，说明C环上C-5位的酮基的存在能够降低A环(C-8和C-6)的活化邻位的亲核性；研究还发现，儿茶素和黄豆苷元可作为抑制异味的最佳组合；不同多酚的异味抑制作用机理研究表明，相比氧化还原反应，通过亲电芳香取代反应的羰基捕获是多酚抑制异味的主要作用途径。..该研究成果能为甜瓜深加工技术提升提供理论依据，更能为其它热敏性果品产业发展提供重要借鉴。