Preliminary Study on the Techniques for the Yellowing Process of Yellow Tea High in γ-Aminobutyric Acid
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Abstract:
Gamma-aminobutyric acid (GABA) has a significant blood pressure-lowering function, but its content in tea is extremely low (only 40~50 mg/100 g). In order to increase the content of GABA in yellow tea, this study examined the from the effects of the raw materials obtained from different seasons (spring and autumn), the yellowing process (wet yellowing process, dry yellowing process or wet-dry combined yellowing process), the facilities for yellowing (natural yellowing, mechanical yellowing, bamboo cage yellowing), and conditions of yellowing process (temperature and time) on the GABA content in yellow tea in the oxygen stress environment of the yellowing process. Based on the results of the sensory evaluation and the analysis of GABA content, a set of technical parameters for the yellowing process to increase the GABA content in yellow tea were obtained. The results showed that the yellowing process could effectively increase the content of GABA in tea leaves. Among them, the fresh leaves in spring were better raw materials than those obtained in autumn; Wet yellowing process was better than dry yellowing process and wet-dry combined yellowing process; bamboo cage yellowing and mechanical yellowing were better than natural yellowing; The yellowing conditions of 50 ℃ and 4 h were beneficial to the formation of a large quantity of GABA. In summary, using spring fresh leaves, wet yellowing process, fermentation machine for yellowing at 50 ℃ for 6 h could lead to the highest increase in the GABA content (up to 127.54 mg/100 g). The research results have provided a new way for the processing of functional yellow tea and an important reference for the future research, development and production of the GABA-rich yellow tea.
