Aroma-increasing Technology of Natural liquid Tea

There are a large number of glycosides with monoterpene enols and aromatic alcohols as ligands in fresh tea leaves. In the process of tea processing, these substances are hydrolyzed by endogenous glycosidase to release volatile ligands, which is an important source of aroma of all kinds of tea flowers and fruits. It has been proved that there are β-glucosides, β-primroside and a small amount of other disaccharides in fresh tea leaves, which are mainly composed of cis-3-hexenol, linalool, methyl salicylate, geraniol, benzyl alcohol and 2-phenylethanol. After picking fresh tea leaves, when processed into all kinds of finished tea, different degrees of spreading should be carried out, together with different processes such as fermentation, green, kneading and drying, to form the aroma quality of tea.

Using dry tea as raw material, the production of all kinds of liquid tea is one of the important contents of deep processing of tea, and the aroma-increasing technology of liquid tea has always been a difficult problem for the liquid tea processing industry. For the liquid tea processed by ordinary process, due to the high temperature thermal extraction of the raw tea in the processing, the temperature of the product is high, the duration is long, and the free aroma components have been volatilized in the processing process, so the aroma is extremely faint, even without any aroma. Synthetic flavor must be added to adjust the flavor. On the other hand, in the process of tea extraction, most of the bound aroma still remains in the tea residue, and some of them enter the tea soup but all exist in the form of bonded state, which can not be used.

The remaining tea residue after extraction is mechanically broken, acidified and hydrolyzed by airtight heating, and the hydrolysate is recovered by distillation to obtain perfume steam and return to liquid tea, thus high-flavor liquid tea can be produced.

(1) processing method

Using the third-grade fried Qingmei tea (produced in Huangshan City, Anhui Province) as raw material, the high-flavor liquid green tea was processed by the following processes:

50% water is added to the remaining tea residue after the raw tea is extracted, and after mechanical crushing, food-grade citric acid is added to adjust the acid to a pH value less than 3. In a closed reactor, 80 ℃ is hydrolyzed for 3 hours, and the volatile produced by hydrolysis is recovered by distillation to obtain perfume steam, which is cooled by a condensation tube and returned to liquid tea to obtain natural high-flavor liquid tea.

(2) results and analysis

The sensory evaluation of ordinary liquid tea and high-flavor liquid tea showed that compared with ordinary liquid tea, the color and taste of high-flavor liquid tea changed little, while the aroma changed from a bit of baking aroma to a strong, refreshing tea with flower and fruit fragrance, which reached the flavor quality of natural and high flavor.

The results of gas chromatography analysis showed that the type and quantity of aroma substances of natural high-flavor liquid tea were much higher than those of ordinary liquid tea. 20 kinds of aroma were detected in natural high-flavor liquid tea, and the content of essential oil was 35.519 micrograms per 500ml, while only 7 aroma components were detected in ordinary liquid tea, and the content of essential oil was only 4.853 micrograms per 500ml.

(3) discussion

All kinds of tea (green tea, black tea and oolong tea) are rich in bonded aroma in the form of glycosides. Although these bound aromas are water-soluble substances, the extraction rate of hot water is very low. This may be related to the existence of bonded aroma substances in tea cells. In the process of tea extraction, most of these bonded aromas still remain in the tea residue, and some of them enter the tea soup but all exist in the form of bonded aroma, which can not be used.

The results show that the bound aroma of tea is mainly composed of cis-3-hexenol, linalool and its oxides, geraniol, methyl salicylate, nerol, benzaldehyde, benzyl alcohol and phenylethanol. After hydrolysis and release, these glycosides become free tea aroma components, which is an important material basis for high-grade tea to present flower and fruit aroma, and can significantly improve the aroma quality of liquid tea.

The bonded aroma in tea is mainly glycosides, and the glycosidic bond belongs to acetal structure, which is easy to be hydrolyzed by dilute acid to form corresponding sugars and ligands (free aroma of tea). In the process of liquid tea processing, the remaining tea residue after extraction is mechanically broken, acid is adjusted with citric acid, hydrolysate is hydrolyzed at high temperature in a closed reactor, and the hydrolysate is recovered by distillation to obtain tea perfume steam, which is cooled and returned to liquid tea to get natural high flavor liquid tea. Because citric acid is not volatile and will not be distilled into the steam of tea perfume with volatile matter, it will not lead to the change of acidity of highly fragrant liquid tea.

By using this technology, the production cost is low, there is no harmful residue, the operation is simple, and it is suitable for industrial production. The liquid tea products produced have natural tea flavor and do not need to be seasoned manually. The aroma quality of the products is obviously better than that of ordinary liquid tea.