Research On The Effects Of Freezing On Black Tea Quality

Black tea in the shoots of tea as raw material is refined by withering, rolling （cut）,fermentation, drying and other typical process. As the tea has specific picking season,significantly limiting the production of traditional black tea. In recent years, research onimproving the processing of black tea are numerous, it was only to improve of the quality,few involved in the preservation and transportation of fresh leaves and the restriction.Production process of black tea is not complicated, but the changes between the variouscomponents in the process are very complex. The chemical composition of fresh leaves ischanged dramatically in process of black tea. Tea polyphenols reduced by more than90%,transformed into other substances such as theaflavins, thearubigins etc. Aroma substanceshave increased from50kinds of fresh leaves to more than300kinds. Part of the caffeine,catechins and theaflavins convert to complexes with fresh and brisk taste. Based on the teathe traditional process, we add a procedure-frozen to explore the effect of freezing ontraditional black tea quality. First keeping the fresh leaves stored in the frozen state forsome time, and then makes them of black tea according to traditional practices.Analyze the cell breakage rate of frozen fresh leaves, the results showed that: Thedamage rate of fresh leaves cell can reach85.7%, which illustrate frozen can moreeffective injury the cells of leaves.Using different processes as traditional black tea and freezing fresh leaves. Explorethe way of making black tea by freezing the fresh leaves. The results showed that: If theprocessing is changed, the main contents of the tea-containing component will also varywith different degrees. Polyphenols and amino acid content were significantly higher thanthe traditional black tea; the contents of caffeine and soluble sugar were decreased.Sensory review also showed that: The sensory quality score in aspects of taste、liquor colorand infused leaves of black tea adding frozen processes were higher than the traditionalblack tea except aroma.In order to further obtain the best combination of freezing time、temperature freezingand fermentation time、fermentation temperature, the author use L9（34） orthogonalexperimental design, and take polyphenols, amino acids, soluble sugar, caffeine, TFs, TRs,TBs and sensory quality as the goal. The results of tea polyphenols orthogonal test analysisshowed that: The condition of A₃B₁C₃D₂（Fermentation time170min, fermentationtemperature22°C, the freezing time9d, freezing temperature-40°C） is most conducive to the accumulation of tea polyphenols. The sensory quality results show that appropriatelyreduced the content of tea polyphenols is conducive to the improvement of tea quality. Theresults of amino acids orthogonal test analysis showed that: The condition of A₁B₁C₁D₁（Fermentation time110min, fermentation temperature22°C, the freezing time3d, freezingtemperature-20°C） is most conducive to the accumulation of amino acids. The results ofsoluble sugar orthogonal test analysis showed that: The condition of A₃B₃C₂D₁（Fermentation time170min, fermentation temperature32°C, the freezing time6d, freezingtemperature-20°C） is most conducive to the accumulation of soluble sugar, And thesensory quality results show that it tastes sweet and synthesized quality is best. The resultsof caffeine orthogonal test analysis showed that: The condition of A₃B₃C₂D_{Fermentationtime140min, fermentation temperature32°C, the freezing time3d, freezing temperature-40°C} is most conducive to the accumulation of caffeine. But there is no obviouscorrelation between the content of caffeine and black tea’s quality, which only to be usedas a referential indicator. The results of TFs orthogonal test analysis shows that: Thecondition of A₂B₁C₂D₃（Fermentation time140min, fermentation temperature22°C, thefreezing time6d, freezing temperature-70°C） is the most favorable conditions to theaccumulation of TFs. The content of theaflavins is highly correlated to the quality of blacktea. The higher the content of TFs, the more they will help improve the quality of black tea.As a result, the contents of TFs should be kept as much as possible in the process. Theorthogonal test TRs analysis shows that: The condition of A1B2C2D2（Fermentation time110min, fermentation temperature27°C, the freezing time9d, freezing temperature-40°C）is most conducive to the accumulation of TRs. However, the tea will become darkand taste poor if the content of TRs is too high. Therefore, the content of TRs should beappropriate.The results of TBs test analysis showed that: The content of TBs in treatmentA₁B₁C₁D₁（Fermentation time110min, fermentation temperature22°C, the freezing time3d, freezing temperature-20°C） is least.In summary: The conditions of A₁B₁C₁D₁、A₃B₃C₂D₁、A₂B₁C₂D₃are conducive to theimprovement of tea quality either increasing the contents of effective biochemicalcomposition or sensory quality;Aroma aspects: Although the total essential oil in A₁B₁C₁D_is low, total number of aromatic substances is higher. The total essential oil and totalnumber of aromatic substances of A₃B₃C₂D₁、A₂B₁C₂D₃are in the middle to all processingsamples, complied with the general standards. The requirements on better black tea to themain contents of the tea-containing component is tea polyphenols, caffeine and TRs haveright amount with amino acids, soluble sugar, TFs highest and TBs as little as possible. So considering the actual cost of production, the condition of A₁B₁C₁D₁（Fermentation time110min, fermentation temperature22°C, the freezing time3d, freezing temperature-20°C）not only beneficial to improve the quality of black tea, but also reduces the production cost,which easier to implement the actual production.