Tea Freeze Dryer

Tea Freeze Dryer

Effect of vacuum freeze-drying on aroma quality of oolong tea

oolong tea is the second largest tea category in China. Its production and export volume is second only to green tea. In recent years, the production and sales volume of oolong tea has increased significantly. At the same time, it is also a tea category with current market competitiveness. In particular, Qingxiang oolong tea is favored by the majority of consumers for its "color green" (dry tea and soup color green or yellow-green), "Xianggao" (with natural flower and fruit aroma), and "thick taste" (mellow and sweet taste). In the processing process of colong tea, how to make Qingxiang oolong tea have both "color", "aroma" and "taste" is the focus and difficulty of oolong tea processing technology research in recent years. Frozen tea Frozen oolong tea oolong tea was first developed in China's Taiwan area. It was directly packaged and frozen after being rolled without drying. Its aroma and taste were superior to traditional colong tea. Wang Wenjie's famous tea has changed the main biochemical components and aroma of the leaves during the storage period. In recent years, there are also a few frozen tea sales in the domestic market, but the moisture content of frozen tea is high and is affected by storage and transportation conditions. , unable to expand the sales market.

At present, vacuum freeze-drying technology is considered as one of the food preservation processing technologies. It can preserve the color, aroma, taste, vitamin C, and other nutrients of fresh food. It has the advantages of a small loss of nutrients, good solubility, long preservation period, and easy transportation. It is widely used in food (vegetables, fruits, instant noodles, seasonings, instant tea), medicine, chemical industry, and other fields, but there is no report on its application in the preliminary preparation and processing of tea. In this experiment, vacuum freeze-drying technology was applied to the processing of fragrant oolong tea to explore the effect of vacuum freeze-drying on the quality and aroma of oolong tea.

1 material and methods

1.1 materials

The test material is colong tea variety Jin Guanyin (also known as Mike No. 1). The raw materials of fresh leaves are collected from the demonstration tea garden of Fujian agriculture * Tea Research Institute. The picking time in the afternoon of April 22, 2004, with fine weather. They are picked according to the picking standard of colong tea in Southern Fujian (2 ~ 4 leaves from the small to the middle opening).

1.2 method

1.2. 1. Preparation method of tea sample

Under the same environmental conditions, the raw materials of fresh leaves of golden Guanyin have the same processing processes of drying, making, killing and initial (package) kneading. They are treated and stored by freeze-drying, frozen storage, and thermal drying. The process flow of each treatment is as follows:

(1) The technological process of freeze-dried tea is as follows: drying green → spreading green → shaking green ← → cooling green (3 times) → killing green → initial (wrapping) kneading → initial drying → vacuum freeze-drying (using oolong tea freeze dryer for drying, pre-freezing → quick freezing → sublimation drying → freeze-dried oolong tea, referred to as freeze-dried tea);

(2) The technological process of frozen tea is: drying green → spreading green → shaking green ← → cooling green (3 times) → killing green → initial (wrapping) kneading → initial drying → low-temperature frozen storage below - 10 ℃ (frozen oolong tea, referred to as frozen tea for short);

(3) The technological process of drying tea (control): drying green → spreading green → shaking green ← → cooling green (3 times) → killing green → initial (wrapping) kneading → initial drying → foot fire (drying colong tea, hereinafter referred to as drying tea).

1.2. 2 aroma detection method

(1) Instruments and reagents: Saturn 3900 / 2100 GC-MS GC-MS of American Varian company; constant temperature blast incubator; vacuum dryer; SPME extraction handle and 100 of sup eco company μ M polydimethylsiloxane (PDMS) extraction head.

(2) Extraction method: accurately weigh 150.0 g of tea sample, place the tested tea sample in the dryer (closed without vacuum pumping), place it in a 40 ℃ blast incubator overnight (more than 12 h), balance the aroma in the dryer, and insert PDMS-100 μ M extraction head is adsorbed for 2 h and tested directly by GC-MS, or placed in the refrigerator at 4 ℃ for several hours. The desorption time of SPME was 5 min.

(3) GC-MS analysis conditions: chromatographic column: DB-5, 30 m × 0.25 mm(id) × zero point two five μ M (film thickness). Carrier gas: helium, purity > 99.999%; Flow rate: 1 ml / min. Column temperature: the initial temperature is 50 ℃, keep for 2 min, rise to 280 ℃ at the heating rate of 6 ℃ / min, and keep for 3 min; Injection port temperature: 250 ℃. Some conditions of mass spectrometry are as follows: ionization mode: EI; Ionization energy: 70 EV; Well temperature: 180 ℃; Well casing: 40 ℃; Transmission line: 280 ℃; Full spectrum scanning, the scanning range is 40 ~ 400 m / Z.

(4) Qualitative and quantitative methods: according to the color spectrum peaks obtained by GC-MS analysis, the aroma components of the tested tea samples were searched by computer spectrum library (Wiley and NIST Library in the United States), combined with the relative retention time, the relevant literature data were consulted for qualitative analysis, and the aroma components were relatively quantified according to the peak area value.

1.2. 3 determination method of the water content of finished tea

Determined by 120 ℃ oven method.

1.2. 4 sensory quality identification

The processed tea samples are vacuum-packed and stored in a refrigerator below - 10 ℃ for 50 days, and then the sensory evaluation of the work quality is conducted by a professional tea evaluator.

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