We all know that drinking tea regularly is very beneficial for our body, as it can provide various nutrients that our body needs. However, due to the special nature of tea leaves, improper storage can easily lead to deterioration, which is mainly caused by the oxidation of chemical components such as chlorophyll in tea leaves under the influence of humidity, temperature, oxygen, and light. This can lead to aging or deterioration of tea leaves, which may also affect our health.
1. Chlorophyll causes tea leaves to turn brown
Chlorophyll has a high content in young leaves and is an important component that gives green tea its color. It is mainly composed of chlorophyll a, which is bluish-green, and chlorophyll b, which is yellowish-green. The proportion of these two components determines the color of the finished tea. Chlorophyll is a very unstable substance and easily decomposes under light and heat (especially under ultraviolet radiation), losing its green color and turning brown. When the content of demetalized chlorophyll reaches 70%, the color of the tea leaves significantly turns brown. The higher the quality of green tea, the higher the chlorophyll content, but it is also more difficult to preserve.
2. Vitamin C is easily oxidized
Vitamin C is an important nutrient in tea leaves, and its content is closely related to the quality of the tea leaves. Vitamin C is also a substance that is easily oxidized. After oxidation, it becomes dehydroascorbic acid, which interacts with amino acids, reducing the nutritional value of tea leaves and causing color fade and loss of freshness. If the retention of vitamin C in green tea is above 80%, the quality of the tea will not change. Once it drops below 60%, the quality becomes noticeably worse.
3. Tea polyphenols affect the taste of tea
Tea polyphenols are closely related to the taste and color of tea soup, and their content determines the concentration of the tea soup. Tea polyphenols themselves are colorless, but they are oxidized and polymerized to form theaflavins and thearubigins, which become brown pigments (high polymers), deepening and darkening the color of black tea soup. In green tea, tea polyphenols are well retained, but they are also prone to oxidation during storage, forming quinone compounds that cause color change. These substances can also react further with amino acids, resulting in the deterioration of the taste of the tea soup.
4. Amino acids affect the freshness of tea leaves
Amino acids in tea plants are mainly concentrated in the tender buds, with a lower content in old leaves. Therefore, the higher the grade of tea leaves, the more amino acids they contain. During storage, amino acids can combine with the oxidation products of tea polyphenols to form dark-colored polymers, which not only reduces the astringency of tea leaves but also loses the fresh taste unique to new tea. During the storage of black tea, amino acids react with theaflavins and thearubigins to form dark-colored high polymers. At the same time, amino acids can also undergo oxidation and transformation under certain temperature conditions. Therefore, the longer the storage time, the more the amino acid content decreases, and the tea leaves gradually lose their freshness.
5. Lipids and carotenoids affect the tea soup
Tea leaves contain about 8% of lipid substances, which can be oxidized and hydrolyzed during storage, resulting in the formation of free fatty acids, aldehydes, or ketones, and producing a sour and rancid taste. The increase in free fatty acid content in tea leaves not only enhances the aroma of tea leaves but also deepens the color of the tea soup. Tea leaves also contain a certain amount of carotenoids, which are yellow pigments and auxiliary components in photosynthesis. They have the property of absorbing light energy and are easily oxidized. The oxidized products emit an odor similar to that produced by stored carrots, leading to a change in the quality of the tea soup.
6. Aromatic substances affect the aroma of tea
Aromatic substances in tea leaves refer to volatile aroma components. As the storage time of tea leaves increases, the aroma decreases while the aged flavor becomes more prominent, especially the refreshing aroma unique to new tea disappears. At the same time, some new compounds are produced during the storage of tea leaves, and sensory evaluation shows the presence of noticeable aged flavor components.
No matter which factor affects the deterioration of tea leaves, it is ultimately not beneficial to our health. Therefore, if you find that tea leaves have deteriorated or deteriorated in daily life, it may be due to problems with your storage methods. Be sure to store the remaining tea leaves according to the correct storage methods to prevent further deterioration.
