Research On Optimization Of Preservation Technology And Related Mechanism Of Longjing Tea

The production of green tea, especially famous green tea, had obvious seasonal restrictions, and as green tea usually experienced a long time from the production, storage and maketing to the consumers, tea quality and its economic valve would suffer greatly decrease, if taken improper packings and storage technologies.This study focus on the control of water content and deoxidizing preservation technology. The preservation effects of different preserving methods were estimated by sensory evaluation, quality components determination and gas chromatography-mass spectrum(GC-MS) for aroma analysis, etc. And quality mechanism of different preservation effects were studied in order to provide theoretical basis for further improvement of preservation technology. The research was developed from three aspects as advances:1. Baking process before preservation was taken and innovated, for the purpose of the assurance of process quality, effective control of water content and the improvement of preservation performance.2. Experiments on different small packings with deoxidizer were carried out to analyze preservation effects and related mechanism.3Control technologies of moisture content and deoxization were applied simultaneously to improve the preservation performance of new packing with deoxization, in order to achieve cooperative preservation effects of the combination. The study obtained conclusions as follows:1. Based on previous studies, a new process for baking and aroma-improving technology was proposed, that taken slow heating rate in baking process. The results indicated that sample treated with slow heating rate was superior to treatment with fast heating rate, whether on the colour, flavor and taste quality of tea or quality stability during storage. This indicated that technologic effects of directly baked at the target temperature, which was often used in present process were not ideal, although it was easy to operate. With further refining of slow heating process parameters, this technology was expected to be directly appllied to practical production.2. A side effect from deoxidizer that moisture was created during the deoxygenation process was first discovered by contrast tests of different small packings adding deoxidizer, which brought increase of moisture content. Due to limited quantity, the add humidity effect on the deoxization packing that a packet makes for a cup of tea was more obvious that impacts its preservation effect, although it has many advantages of preservation performance and a value of being popularized.3. Control technologies of moisture content and deoxization were applied simultaneously to improve the preservation performance of new deoxization packing that a packet makes for a cup of tea. Clear results were concluded that using desiccant and deoxidizer simultaneously could achieve cooperative preservation effects on whether color of dry tea or quality4. Results indicated that, during the tea deterioration process, the aroma components of tea change regularly. The results of aroma detection were in good agreement with sensory results. The dynamic detection results of different treated tea samples under high temperature storage for sixty days showed that relative content and stability of alcohols, especially linalool, can be used as the positive index of the freshness of flavor quality. While aldehydes and ketones, especially the characteristic components of stale taste, such as (E,E)-2,4-heptadienal,(E,E)-5-octadien-2-one and β-ionone can be used as reverse indexes. There was no obvious relationship of hydrocarbons, ester and nitrogenous compounds to the deterioration degree of tea. In addition, there may be a certain relationship between oxygen heterocyclic and stale taste. As alcohols decreased and aldehydes and ketones increased steadily along with the extension of storage time, this relationship may be due to alcohols oxidation, which converted to aldehydes, ketones and further into oxygen heterocyclic. It can be seen that, like tea polyphenols and amino acids of green tea, oxidation reaction may be the main reason of tea aroma deterioration.In addition, flavor components, such as tea polyphenols, amino acid; and present-color components, such as chlorophyll, had no significant changes during the tea deterioration process, it’s likely to be because gas molecules in flow condition has higher activation energy, which are more likely to be oxided in the same environment condition. As the preservation experiments usually need a long experiment period, and limited to manpower, materials and seasonal factors of tea production, this study was not comprehensive. It still needs us to have a further research, and do some more improvement.