炒籽胡麻油中美拉德反应源吡嗪类特征香气形成机制的研究

Consumers loved flaxseed oils deeply based on their distinctive aroma and rich nutrition. The applicant’s earlier research found the Maillard reaction source of volatile pyrazine compounds (MRP) showed significant contribution to the overall characteristics aroma profile of roasted flaxseeds oils’ volatile aroma, though the definite mechanism of formation was not clear until now. Therefore, the project was prepared to accurately analyze characteristic aroma components of flaxseed oils generated from MRP and their growth and decline laws by GC-O-MS combined with the standard library and mass spectrometry, and identify the key precursor substances and intermediate products participated in the formation process of MRP by using the combination of UPLC-MS/MS and NMR techniques. Then the synthesizer model of roasted flaxseeds’ volatile aroma generated from Maillard reaction, which make the formation mechanism of characteristic aroma from MRP clear, was established and verified gradually using the substrate to generate products pathway by using stable isotope 13C tracer and HS-SPME/GC-MS techniques. While the fatty acid composition of roasted flaxseeds oil was analyzed by combination with blank control and the MRP synthesizer model, effect of lipid oxidation products on each step of characteristic aroma synthesis generated from Maillard reaction source was revealed, and the mechanism of "lipid-Maillard" reaction synergy was illuminated. These results would help us to understand the specific formation mechanism of characteristic aroma of flaxseed oils generated from MRP after being roasted. The theoritical and practical support would be provided with flaxseed oil product’s quality control during roasting process through the project’s research and implementation.

胡麻油因具有独特香气和丰富营养成分而备受消费者青睐。申请人前期研究发现Maillard反应源吡嗪类化合物（MRP）对炒籽胡麻油整体特征香气轮廓贡献显著，但其具体形成机理尚不清楚。故本项目拟使用GC-O-MS技术结合标品库、质谱图库准确鉴析MRP特征香气，并采用UPLC-MS/MS、NMR等技术及多元回归分析方法筛选鉴定参与MRP香气形成的关键前体物质及中间产物，构建相应特征香气合成模型，再使用稳定同位素13C示踪及HS-SPME/GC-MS等技术对模型进行底物生成产物的逐步验证，明确炒籽胡麻油MRP特征香气的形成机制；通过分析炒籽胡麻油脂肪酸组成，结合空白对照和MRP特征香气合成模型，揭示脂质氧化产物对MRP特征香气合成各步骤的影响，阐明“脂质-Maillard”反应生香的协同作用机制。本项目研究有助于明晰炒籽胡麻油MRP特征香气形成的具体机制，为我国炒籽胡麻油品质控制提供理论和实践依据。

围绕上述任务及目标，结合当前国内商业胡麻籽油生产所采取的主要“炒籽-压榨”工艺环节，采用GC-O-MS技术、气味活度值（OAV）计算及多元回归分析等手段筛选鉴定MRP特征香气构成物质主要为吡嗪类挥发性物质，还有个别杂环类挥发性物质含量因胡麻品种、分析条件、热处理温度和时间等因素而存在动态差异，结合既有文献阈值报道可以确定吡嗪类挥发性物质是胡麻“炒籽-压榨”环节主要发生美拉德反应的不同产物，具有强烈的烤香和坚果味香气，是炒籽胡麻油的主要风味物质。.基于上述结论，课题组利用中性蛋白酶和风味蛋白酶对胡麻籽粕蛋白进行双步酶解，并选择不同水解度酶解产物与不同还原糖（葡萄糖和果糖）的组合构建了12组美拉德反应生香模拟反应体系，研究发现不同美拉德反应组产生的挥发性物质构成的种类和含量各不相同，说明反应底物来源对体系挥发性香气具有显著的影响（P≤0.05），并且随着水解度的增加，模拟美拉德反应体系中的吡嗪类化合物种类及含量逐渐增多，对MRP生成最优美拉德反应体系的氨基酸和多肽分子量测定发现，与吡嗪类香气形成有关的主要前体物质构成主要为天冬氨酸、谷氨酸、异亮氨酸、亮氨酸、酪氨酸、苯丙氨酸、赖氨酸和脯氨酸，肽分子量主要集中于128-500Da。.胡麻籽转录组分析表明，不饱和脂肪酸代谢通路中可注释到8个差异基因，说明胡麻油香气差异与胡麻籽生长过程中脂质氧化途径有关，然而，在不同温度炒籽过程中（≤200℃，30min）胡麻油脂肪酸的组成及相对含量显著变化，理化指标均符合国家标准（GB2716-2018）；另外，氧化加速实验表明α-生育酚的含量在氧化初期急剧下降消失，其特征挥发性风味物质主要为醛类、酮类、醇类化合物等，由此表明，炒籽过程胡麻油的特征香气主要来源美拉德反应过程，“脂质-Maillard”反应协同反应过程对胡麻油MRP特征香气生成贡献不大，但醛类挥发性物质可能对MRP特征香气的释放造成一定影响，其互作机制还有待深入研究。上述相关研究可为胡麻籽油的品质提升和风味改良提供理论基础。