Effect Of Enzymes On Extraction And Fermentation Characteristics Of Summer And Autumn Dried Tea Leaves

In recent years,instant black tea has been increasingly welcomed by customers for its fashion and convenience. Traditionally, the finished or semi-finished black tea was chosen as the raw material, then through extraction and concentration, finally processed into instant black tea, but it showed the shortcomings in high cost and long cycle. With the rapid development of instant black tea production,the problem of material for high-quality and low-cost and of method for time-saving and high-efficiency is urgent to solve. Summer and autumn tea are rich in biochemical components, suspension fermentation method is easily to control and operate, combine the two and apply them to the production of instant black tea, and that will be a great question for study in promoting the quality of instant black tea. Therefore, this paper first studied the effect of particle size and extraction methods on the extraction of effective components, and optimized the conditions of composite enzyme-assisted extraction; on the basis of that, selected suitable exogenous PPO for tea liquor fermentation, and then further optimized the parameters of suspension fermentation; using these technical parameters, processed fresh tea leaves of summer and autumn into instant black tea, and analyzed the quality differences. This provided a thought for increasing utilization of fresh tea leaves and improving the quality of instant black tea.The main results were as follows:1. To study the effect of tea particle size on the extraction of quality components, directly dried fresh leaves was chosen as the raw material, after extracted under medium temperature, the main biochemical components of material were determined. The results showed that the contents of tea polyphenols, amino acid and caffeine increase at first and then tend to be stable with the prolongation of extraction time. The dissolution rate changes with different particle size and extraction time. Extract the material which was crushed into the same particle size, the dissolution rate grows fastest in the early stage(0-15 min). At the different particle size, the highest extraction yield order of tea polyphenols,caffeine and catechins was 0.23mm>0.63 mm>1.25 mm>1.60 mm, and for amino acid, the order was1.25 mm>1.60 mm>0.63 mm>0.23 mm. The smaller particle size, the faster dissolution rate, and the time to the highest extraction yield was reduced.2. The effect of different extraction methods on the extraction of effective components were studied, and optimized the conditions of composite enzyme-assisted extraction. The results showed that it was very preferable by using composite enzyme(cellulase and pectinase) to extract the effective components, furthermore,the extraction conditions of this method was mild and the manipulation was simple. The extraction rate of tea polyphenols, amino acid and water extracts were used as the response value, on the basis of single-factor test, the optimized extraction conditions using a orthogonal design of four factors three levels were extraction temperature 50℃,extraction time 75 min, pH 5.0, adding 0.2%composite enzyme, under the conditions, the extraction rate of effective components were 77.9% of polyphenols,70.62% of amino acids, 83.05% of water extracts, and 82.13% of caffeine, respectively.3. The ability of PPO from different source catalytic oxidize catechins into theaflavins was compared with suspension fermentation method. The results showed that during the fermentation, with the enzymatic action of exogenous PPO, total catechins decreased rapidly in 15 min, and decreased slowly in 15-60 min, then tended to steady. Among 8 kinds of catechin monomer, EGCG reduced most,the reduction of EGC, ECG and EC depended on the type of enzyme sources. The main monomer of theaflavins catalyzed by exogenous PPO was TF, the ability of PPO from different source catalytic oxidize catechins into theaflavins in order was tea fresh leaves>bergamot pear>crystal pear>housi>banana>crown sydney>apple.Sensory evaluation of fermented tea liquid demonstrated that housi,crystal pear and bergamot pear fermented better.4. The main conditions influence suspension fermentation were carried out by single factor experiment, on the basis of that, Plackett-Burman design was used to select the key factors which affect the value of theaflavins in the suspension fermentation, amount of enzyme,fermentation temperature,fermentation time,oxygen flow rate were chosen as significant factors,and further optimized by using orthogonal design. The optimized process parameters in suspension fermentation were add 7.5g enzyme,fermentation temperature 40℃, fermentation time 30 min, oxygen flow rate1.0L/min, under the conditions the concentration of theaflavins was 0.328mg/ml.5. Chose 11 varieties of tea fresh leaves from summer and autumn respectively as the raw material,and fermented into instant black tea. Determined main biochemical components of raw material, and analyzed the difference among varieties. Determined main biochemical components of instant black tea,and evaluated the sensory quality of instant black tea. It turns out that, there were significant differences among the biochemical components of different varieties of tea, and exhibited a larger variation in components of tea; total theaflavins and monomer concentration were different in the instant black tea fermented with different raw materials; instant black tea fermented with summer tea showed better in liquid color and flavor, and that fermented with autumn tea performed better in aroma, Tengcha in summer got the highest total score of sensory quality.