酵母抽提物中风味活性物质及其在加工中变化规律的研究

Yeast extract (YE) is a kind of super natural seasoning, contains rich amount of flavor substances such as free amino acids, 5’-nucleotides and peptides. As an important ingredient, YE is widely used in foods such as meat products, soups, sauces, instant foods, et al., providing meaty, brothy, umami flavor. Flavor-active compounds are divided into odor-active compounds and taste-active compounds. .As the flavor of YE, current results are focused mainly on the volatile components of YE, and until now, the knowledge of flavor precursors including taste-active compounds of YE are very limited,and not be studied systematically. .In this study, here employed are the advanced flavor analyisis techniques including gas chromatography-olfactrometry-mass spetrometry (GC-O-MS), and isolation/purification techniques such as gel filtration chromatography (GFC),RP-HPLC,LC-MS/MS,NMR,et al., combining with sensory evaluation such as taste dilution analysis (TDA), to study the following aspects of yeast extract:(1) analysis of flavor precusors,including purification and identification of taste-active compounds; (2) model of quantative structure and activity relationship (QSAR) of taste-active compounds; (3) relationship of odor-active compounds generated from thermal process with flavor precursors. By the analysis of the taste-active compounds such as umami and kokumi substances deeply and thoroughly, and establishment of their varying pattern,so it is possible to provide scientific foundation to the preparation of yeast extract product with much better flavor qualities.

酵母抽提物（YE）是一种优良的天然调味料，富含游离氨基酸、5’-核苷酸及肽等风味物质，广泛用于肉制品、汤料、酱和方便食品中。风味活性物包括气味活性物及滋味活性物。以往有关酵母抽提物中风味物质的研究，缺乏对其中滋味活性物质的分析，更缺乏对其中风味前驱物及其受热产生气味物的系统研究。本课题拟采用先进的风味分析技术，包括气相色谱-嗅闻-质谱（GC-O-MS）技术以及食品分离纯化技术例如凝胶过滤色谱、反相液相色谱、液-质联用、核磁共振等技术，结合滋味稀释分析（TDA），研究（1）酵母抽提物中风味前驱物分析，重点是滋味活性物质的分离纯化、鉴定；（2）滋味活性物质定量构效关系模型；（3）风味前驱物酵母抽提物加热后产生的关键气味活性化合物，与风味前驱物包括滋味活性物质的相关性。旨在深入剖析酵母抽提物的风味前驱物及关键风味物质，并探索其在加工过程中的变化规律，为制备风味质量更高的酵母抽提物提供科学依据。

酵母提取物（yeast extract，YE）中的挥发物与不挥发物决定其特征香气和滋味。目前，有关热反应后YE 的特征香气和滋味的研究较少；香气活性成分与前驱物之间的关系还不清楚。本研究主要采用气相色谱-嗅闻-质谱（GC-O-MS）技术以及超滤、凝胶过滤色谱、反相高效液相色谱、液-质联用等技术，结合滋味稀释分析（TDA），研究酵母抽提物中风味前驱物分析以及香气活性化合物/滋味活性化合物的鉴定。重要结果：.（1）前驱物与气味化合物的相关性：以及牛肉香气化合物的生成机理研究：温度的增加使烤香、坚果香特征变得更加强烈；前驱物（氨基酸、糖、核苷酸、肽）含量与气味化合物呈负相关。.（2）利用响应面优化得出了以YE 为主要反应物的牛肉味样品，较优条件为：YE 为21.11 %、硫胺素为0.79 %、木糖为2.08 %、半胱氨酸为1.01 %、反应时间为106 min、反应温度为123 ℃、pH 值为5.0。采用13C5 木糖标记体系分析了牛肉香气化合物（吡嗪类、呋喃类）的形成途径。结果表明，吡嗪类的C 骨架来源于木糖的C5，Cys 的降解产物在含硫肉味化合物的形成途径中起着重要作用，呋喃类化合物的生成没有肽的参与，直接由糖降解生成。.（3）不同温度热处理YE后滋味肽的分布情况和味觉行为：从不同温度热处理后YE中鉴定出15种不同结构的鲜味肽、4种苦味肽。含有谷氨酸的肽段鲜味TD 因子最高为8，最低为6，其中三肽Pro-Glu-Thr 的TD 因子为8 苦味肽Arg-Leu 的FD 为9。分析了上述肽在不同浓度和不同pH值溶液中的滋味特征。.（4）YE中的不同滋味肽的反应活性研究：肽可以单独通过热降解发生断裂；每一个肽都会发生环化反应；肽类可以与糠醛进行交联。肽的反应活性跟所组成的氨基酸结构有关，Glu-X、Gln-X 的反应活性强于Arg-X（X 为未知氨基酸残基）。