Collection of the hottest tea preservation techniq

Tea preservation technology collection

3. Aromatic substances

under aerobic environment, with the extension of storage time, the aroma of tea gradually weakens, the sweet taste gradually loses, and the aging taste begins to show, until the quality is completely degraded, aged, and loses drinking value. Tea contains more lipids, especially some free unsaturated fatty acids, which are important chemical basis of tea aroma, but they are also some very unstable components. Under high temperature and aerobic conditions, lipids will be hydrolyzed to form free fatty acids. The further oxidative decomposition of free fatty acids will produce volatile substances such as low molecular aldehydes, ketones, alcohols with bad smell, which is one of the important reasons for the changes of tea aroma during storage. The changes of free fatty acids such as linoleic acid and linolenic acid during storage are basically similar to those of lipids

at present, it is generally believed that green tea has "new tea flavor" components, mainly dimethyl sulfur, n-nonaldehyde, cis-3-hexene acetate and some other unknown components. Under the condition of oxygen, these components have a very obvious downward trend during storage. After storage for 2 months, dimethyl sulfur is reduced by 43% and n-nonaldehyde is reduced by 80%, Cis-3-hexene acetate decreased by 39%. On the contrary, 1-penten-3-ol, cis-2-penten-1-ol, 2,4 heptanaldehyde, 3,5-octadiene-2-one and propionaldehyde were newly produced during storage. These substances are produced gradually during storage, and the content increases gradually with the extension of storage time. These substances have not been found before storage (in new tea). These compounds have grass gas and oil odor. Because their threshold value is very small, even if the amount produced is very small, they will feel unpleasant aging odor

in addition, carotenoids are also easy to be oxidized. During the storage of green tea, 2,6,6-trimethyl-2-hydroxycyclohexanone, β- Cyclocitral, α- The oxides of carotene such as Viola ketone, 5,6 epoxy Viola ketone and so on also increased to a certain extent. These compounds are also closely related to the aging taste of green tea

the aroma changes of black tea during storage are more complex. With the hydrolysis and automatic oxidation of lipids, in addition to the increase in the content of some aged substances, many substances with flower and fruit aroma in black tea, such as phenylethanol, nerol, etc., and the content of isobutyraldehyde, isoamyl alcohol, linalool, etc., which are beneficial to quality, are significantly reduced. This change not only makes the tea lose its fragrance, but also shows the taste of aging and rancidity

4. Vitamin

vitamin C is one of the nutrients required by the human body, which is rich in green tea. During the storage of tea in an aerobic environment, vitamin C will be reduced due to a series of chemical changes such as hydrolysis and browning, which will reduce the nutritional value of tea. Due to the oxidation of vitamin C, 2,3-ketogulonic acid is very easy to react with amino acids; At the same time, the dehydration and decarboxylation of 2,3-ketoguronic acid will produce brown hydroxy sugar aldehyde polymer. It makes green tea brown, the color of tea and soup darker and darker, and loses the freshness of tea, thus reducing the quality of tea

according to the research, after green tea was stored in an aerobic environment for 4 months, vitamin C decreased from 306.75mg/100g before storage to 191.59mg/100g, a decrease of 37.54%, after 8 months of storage, it decreased to 173.57mg/100g, a decrease of 42.32%, and after 12 months of storage, it decreased to 166.10mg/100g, a decrease of 45.85%. The study pointed out that when the vitamin C retention was more than 80%, the quality changed less. When the retention decreased to less than 60%, the tea could be felt to have deteriorated significantly

5, chlorophyll and other chemical components

chlorophyll is the main component of green tea cup color, and its change will have a great impact on the color. Chlorophyll is a very unstable substance, which is prone to magnesium removal reaction under the action of water, light and temperature during storage. After 12 months storage, the total chlorophyll content of green tea cups decreased by 12.76%. Obviously, after a long period of storage. Not tight will make the green color of green tea fade, and will make the color dark and brown, which is closely related to the demineralization reaction of chlorophyll. According to the research, when the conversion rate of chlorophyll into demethylated chlorophyll in green tea is about 40%, the color of tea can remain green. When the conversion rate of chlorophyll into demethylated chlorophyll is about 70%, the color of tea will turn brown significantly

second, the impact of tea storage environment

through the above understanding of the main components of tea, we can know that the main reason for the aging and deterioration of tea is some chemical components in tea, It is the result of a series of chemical changes under certain storage conditions. Although there are many conditions affecting these chemical changes, the main factors leading to these changes are oxygen, temperature, humidity, light and packaging

in the absence of enzymatic action, substances are slowly oxidized by molecular oxygen, which is called automatic oxidation. In addition to the deterioration caused by moisture, temperature and light, the deterioration caused by oxidation is the most important during the storage of tea. As we all know, the oxygen content in the air accounts for about 21%, and its chemical properties are very active. It can oxidize polyphenols, chlorophyll, lipids, vitamins, ketones, aldehydes and other substances in tea. Most of the substances produced by the reaction are unfavorable to the quality. Oxygen can also promote the growth and reproduction of microorganisms, making tea moldy

according to the research, under the condition of oxygen content of 1%, the color of green tea after storage for 4 months is almost unchanged. At present, it changes in improving the performance of the tape. When the oxygen content rises to more than 5%, the color of green tea will change greatly after storage for 4 months. It shows that under certain conditions, high oxygen content will aggravate the automatic oxidation of tea

in order to prevent the automatic oxidation of stored tea, the only way is to isolate tea from oxygen and reproduce the experimental process through curve traversal. The method often used in the past is to vacuum and fill nitrogen or carbon dioxide during tea packaging, so as to reduce the oxygen content in the packaging container. However, because oxygen will slowly penetrate into the container through the packaging materials during storage, the oxygen concentration in the packaging container will slowly become close to the oxygen content in the air. At present, the most effective method is to use deoxidizer for fresh-keeping, which is to make the tea in the package in a relatively oxygen free and dry environment within the shelf life by means of chemical deoxidization, dehumidification and other air adjustment. Deoxygenation fresh-keeping method has the characteristics of simple operation, low cost and remarkable fresh-keeping effect. In addition, microorganisms in tea, like other organisms, need aerobic respiration for normal metabolism. Most microorganisms on dry food are aerobic. The existence of oxygen (8) bricklaying is conducive to their growth and reproduction, and sealing the anaerobic environment will suffocate them and die. Therefore, the use of vacuum plus deoxidizer for oxygen isolation storage of tea can not only prevent mildew, but also delay the aging of tea, reduce the consumption of polyphenols, amino acids, vitamins, chlorophyll, aromatic substances and other important components in tea, which are difficult to start at this time, and ensure the quality of tea during a long storage period

(to be continued)