Dynamic Changes in Quality and Composition of Oolong Tea Made with Fresh Bixiangzao Summer Tea Leaves during Processing
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Abstract:
Using three- four fresh leaves of Bixiangzao summer tea leaves as the raw materials, oolong tea was produced following the procedure involving withering, shaking, kill-green (de-enzyming), rolling and drying steps. The biochemical components of the samples generated from the tea processing and the dry tea samples were analyzed, and the aroma components were detected by solid phase microextraction-gas chromatography-mass spectrometry (SPME/GC-MS). Combined with sensory evaluation, the dynamic changes of quality components and quality formation of Bixiangzao fresh leaves during oolong tea processing were examined. The results of sensory evaluation showed that the oolong tea had amellow taste and a floral aroma. Quality component analysis showed that tea polyphenols, catechins, caffeine, soluble sugars, flavonoids and water extracts showed an overall downward trend (decreases by 5.32%, 3.96%, 0.48%, 0.38%, 22.35%and 2.77%, respectively, from fresh leaves to dried tea),whilst the content of free amino acids showed an overall upward trend (an increase by 12.88%from fresh leaves to dried tea). The analysis of volatile components revealed that the overall contents of volatile components (hydrocarbons, ketones, aldehydes and other substances) showed an upward trend, whilst the contents of alcohols, esters and phenols showed an overall downward trend. Among them, trans-nerol, phenylethanol, dihydrolinalool, benzaldehyde, β-ionone, indole, α-farnesene, α-ylenoleneand geranyl acetone can be used as the characteristic aroma components of Bixiangzao summer oolong tea. The processing of oolong tea promotes the gradual decrease of bitter and astringent tastes and greenish substances, and the gradual increase of sweet, mellow, and floral and fruity substances, which is conducive to the formation of the taste and aroma of this kind of tea, and provides a scientific reference for the utilization of summer tea resources.
