Aroma is one of the key factors that determine the quality of tea. The harmonious and pleasant aroma is not only an important reference standard for the evaluation of the product grade of famous green tea, but also an important basis for consumers to choose green tea products. Chestnut aroma is one of the characteristic aromas of high-quality green tea.
First, the classification of the aroma of chestnut incense
Different types of tea have different aroma characteristics, as far as green tea is concerned, there are roughly 5 kinds of aroma types: milli-scented type, tender fragrance type, floral type, fragrance type and chestnut type. Among them, chestnut aroma is one of the characteristic aroma types of high-quality green tea, which is mainly manifested as similar to the aroma characteristics of cooked chestnuts, with a strong and long-lasting aroma, and is also described as roasted incense.
SPRING
With the maturity and refinement of sensory technology, according to the differences in sensory representations such as chestnut aroma type performance and aroma intensity, the modern sensory review subdivides chestnut incense into different fragrance types such as tender chestnut, chestnut and cooked chestnut. Chestnut incense is a kind of nut aroma based on specific varieties, mostly seen in the production of high-grade green tea and individual varieties of tea with just the right fire; tender chestnut fragrance is based on the chestnut flavor, highlighting the soft, fresh and elegant tea aroma, more common in raw materials, finely harvested high-grade green tea; cooked chestnut incense is manifested as the aroma characteristics of the transition from chestnut incense to high fire incense, generally formed under the processing conditions of foot fire [1].
Second, the aroma composition of chestnut incense
The aroma composition of green tea is more similar to that of fresh leaf raw materials, the aroma is elegant, there are more than 300 kinds of aroma compounds, the content is about 0.005%-0.03%, the main aroma components are linalool and its oxides, methyl salicylate, geraniol, caproic acid - cis-3-hexen ester, syringene, farneene, nerolidol and the like. According to its structural characteristics, it is mainly divided into four categories: terpenes and their derivatives, fat derivatives, aromatic derivatives and nitrogen-containing heterocyclic compounds.
Chestnut fragrance is an overall sensory evaluation formed by the synergy of many aroma components in a certain proportion and through synergy. Some of the many aromatic components play an important role in their fragrance, which we call "key aroma substances". It was found that the 12 key aroma components of isobutyral, hexanal, heptaldehyde, nonaldehyde, decanal, phenylacetaldehyde, linalool, 1-octen-3-ol, 1-en-3-one, β-ionone, para-umbelliferant hydrocarbons, and ethyl caproate play an important role in the presentation of green tea chestnut. These 12 key aroma substances were prepared into aroma solutions according to the proportions in the original tea soup, added to the solution based on high-purity aroma tea soup, and scored the six characteristic attributes of cooked sweetness, foot fire, flower and fruit fragrance, fragrance, grass flavor and tender fragrance, respectively, and the similarity values of the simulated system samples of the three aroma types and the standard control samples were above 0.97, and the reconstruction effect was better, and the contribution of these 12 key aroma components to the green tea chestnut aroma was verified [2].
Third, the formation mechanism of chestnut incense
The aromatic substances in tea are mainly derived from three aspects: one is the free aroma substance contained in the fresh leaf itself; the second is the aroma substance formed during processing; and the third is the adsorption effect of the tea on the exogenous aroma (for example, the preparation of jasmine tea). Among them, pathway two is the main way of tea aroma substance generation, the process generally occurs physical and chemical changes in thermal action or enzymatic reactions.
In terms of physiological structure, the aromatic substances in tea are partly present in the leaves in a free-form form, and partly in the form of glycosids in vacuoles or other organelles separated from endogenous glycosidases. When tea leaves are mechanically damaged during processing, the internal structure of the cell is destroyed, causing the glycosidic substance to come into contact with its hydrolases to release the aroma.
From the perspective of chemical mechanism, the accumulation of green tea aroma components mainly includes four aspects:
(1) Aromatic compounds such as carotenoids caused by catechin oxidation to form β-ionone and related structures;
(2) Alcohols and aldehyde aroma compounds of 6 carbons generated by peroxidation and degradation of lipids;
(3) Amino acid decarboxylation and oxidative deamination are converted into corresponding aldehydes, or Maillard reactions occur with sugars and catechins to generate substances with caramel aroma and baking aroma such as pyrazine, pyrrole, furan, furfural, etc.;
(4) Glycosid aroma precursors are hydrolyzed under the action of glycosidases to generate corresponding alcohols. Based on the study on the effect of exogenous addition of theanine/sucrose on the formation of chestnut flavor quality, it was found that theanine is an important basic substance for the formation of chestnut aroma, and the Maillard reaction is one of its formation pathways, and whether there are other formation pathways needs to be further explored.
Fourth, the effect of the process on chestnut incense
The spreading, killing, kneading and drying of fresh leaves are the main processes of green tea processing, and each process plays a specific role in the formation of the quality of green tea, and at the same time has an important contribution to the formation of the aroma of tea. To put it simply, spreading is the process of hydrolysis of macromolecular storage substances to generate simple substances, and also the accumulation process of tea aroma precursor substances; killing is the process of volatilization and loss of low boiling point substances, the process of exposing high boiling point substances, and also the process of significantly increasing the content and type of aromatic substances at high temperatures; kneading is the process of mixing polyphenols with other various contained substances, and it is also a process that affects the aroma content and type of tea; drying is an important stage of various thermophysical chemical reactions, and it is also a process of flower and fruit aroma, The final stage of high incense formation and fixation.
The way of drying, temperature, time and moisture content all directly or indirectly affect thermophysical chemical reactions, thus affecting the aroma performance of tea leaves. Studies have shown that:
(1) Drying method: Segmented drying makes the tea water evenly distributed, which is conducive to the formation of tea quality, and the first drying uses drying to dry the water in the tea leaves in a timely manner than stir-frying, which is conducive to the formation and transformation of volatile substances and promotes the formation of aroma; the convection and conduction of heat transfer is more likely to produce chestnut aroma than radiation, and the tea-like chestnut aroma under the box hot air convection mode is the most concentrated [4].
(2) Drying temperature and time: temperature and time have a regulatory effect on the formation of tea aroma, and the aroma intensity of chestnut incense has a peak in the formation process, and then at different temperatures and times, the aroma intensity and type of chestnut incense will change to varying degrees.
(3) Moisture content: The moisture content will affect the wet heat process or dry heat process by changing the environment in which the tea is located, thereby affecting the formation of aroma. Proper control of fire attack and the degree of water dispersion of tea leaves is conducive to obtaining a good fragrance. At the same temperature, the low moisture content facilitates the formation of more pyrazine compounds, which is beneficial to the formation of chestnut incense.
The above research results are helpful to enrich the qualitative and quantitative basic research of tea flavor enrichment and enrich the aroma composition and aroma theory, which can provide important theoretical support for the precise regulation and directional processing of tea product aroma.
Original text of the paper:
[1] Mingming Zhang, Yongwen Jiang, Haibo Yuan*, Yanqin Yang*, Yuliang Deng, Chunwang Dong, Jia Li, Jinjie Shui, Jinjin Wang. Research progress on the formation and process of green tea chestnut fragrance[J].Chinese Agricultural Science Bulletin,2020,36(02):129-137.
[ZHANG Mingming,YIN Hongxu,DENG Yuliang,YAO Yuefeng,JIANG Yongwen,SHUI Jinjie,YUAN Haibo*,YANG Yanqin*.Analysis of key aroma components of green tea based on HS-SPME/GC×GC-TOFMS/OAV[J].Food Science,2020,41(02):244-252.
[3] Mingming Zhang#, Yanqin Yang#, Haibo Yuan*, Jinjie Hua, Yuliang Deng*, Yongwen Jiang, Jinjin Wang. Contribution of addition theanine/sucrose on the formation of chestnut-like aroma of green tea[J]. LWT,2020,129. 109512.
[ZHANG Mingming,JIANG Yongwen,SHUI Jinjie,WANG Jinjin,YUAN Haibo*,YANG Yanqin*.Effect of drying method on green tea chestnut aroma[J].Food Science,2020,41(15):115-123.
Tea Precision Processing Team, Tea Research Institute, Chinese Academy of Agricultural Sciences