Effects of anaerobic time on main mulberry leaf tea components such as γ-aminobutyric acid and sensory quality

Abstract

[Objective] To investigate the effects of anaerobic time on the main mulberry leaf tea components such as γ-aminobutyric acid (GABA) and its sensory quality for optimizing production process of mulberry leaf tea with high GABA content, so as to provide the theoretical reference for the high-quality mulberry leaf tea production.

[Method] The fresh and tender leaves of Nongsang No.12 were used as materials, processed with green tea type (S1) and black tea type (S2) processing technology respectively. Different anaerobic time treatments (2, 4 and 8 h) were set after greening and rolling respectively, with anaerobic 0 h as the control. The effects of different anaerobic time treatments on GABA and other main components of mulberry leaf tea and their sensory qualities were analyzed.

[Result] The sensory quality of mulberry leaf tea prepared after anaerobic treatment was better than that of the control group. In S1, anaerobic treatment for 8 h had the best sensory quality, with uniform appearance, bright green color, good clarity, sweet aroma, bean fragrance, mellow and sweet taste, bright yellow-green soup color, tender and even leaf bottom. In S2, the highest score in the evaluation of anaerobic treatment for 2 hours, the appearance was still uniform, the clarity was still good, the brown color was still bright, and the aroma was bean-flavored, with floral fragrance, rich taste, yellow and bright soup color, tender and evenly-shaped leaf bottom. Anaerote could effectively increase the GABA content in mulberry leaf tea. With the extension of anaerobic time to 8 h,the content of GABA in S1 reached 2.70 mg/g,and the content of GABA in S2 reached 6.55 mg/g; the content of flavonoids in S1 increased to 86.04 mg/g when anaerobic time extended to 8 h, and the content of flavonoids in S2 decreased significantly ( P<0.05, the same below) to 23.14 mg/g when anaerobic time extended to 8 h. After anaerobic treatment, the tryptophan content in S1 and S2 mulberry leaf teas increased significantly, reaching 4.53 and 5.07 mg/g, respectively, at 8 h of anaerobic time. The effect of anaerobicity on serotonin in S1 and S2 mulberry leaf tea was different. The content of serotonin in S1 decreased significantly at the initial anaerobic stage (0–2 h), but gradually recovered with the extension of anaerobic time and the difference gradually disappeared. The content of serotonin in S2 was significantly increased, and the content of serotonin was 100 ng/g after anaerobic 8 h.

[Conclusion] In the development of mulberry leaf tea products with high GABA content, the processing technology is the best when fresh leaves spreading for 1.5 h, rolling for 30 min, vacuum anaerobic treatment for 8 h, and drying temperature of 80 °C. Tea made by such processing technology aroma is sweet and floral, the taste is mellow, and the color of the tea soup is bright orange.

Abstract

摘要：【目的】明确厌氧时间对桑叶茶γ-氨基丁酸(GABA)等主要成分及其感官品质的影响, 优化生产高GABA含 量桑叶茶的制作工艺, 为生产优质桑叶茶提供理论依据。 【方法】以农桑12号新鲜柔嫩叶片为材料, 分别按绿茶型 (S1)和红茶型(S2)加工工艺进行处理, 并在杀青和揉捻后设置不同的厌氧时间(2、4和8 h)处理, 以厌氧0 h为对照, 分析不同厌氧时间处理对桑叶茶GABA等主要成分及其感官品质的影响。 【结果】厌氧处理后制得的桑叶茶感官品质 优于对照组, S1中以厌氧处理8 h感官品质最优, 外形勻整、色泽绿尚亮、净度尚好, 香气甜香带有豆香, 滋味醇爽回 甘, 汤色黄绿明亮, 叶底柔嫩尚勻整;S2中以厌氧处理2 h的审评得分最高, 外形尚勻整、净度尚好、褐尚亮, 香气豆香 带花香, 滋味浓醇, 汤色黄且明亮, 叶底柔嫩欠勻整。厌氧能有效提高桑叶茶中的GABA含量, 随厌氧时间延长至8 h, S1中GABA含量达2.70 mg/g, S2中GABA含量达6.55 mg/g; S1中黄酮含量随厌氧时间延长至8 h时为86.04 mg/g, S2中黄酮含量则显著降低( P<0.05,下同), 至8 h时为23.14 mg/g。厌氧处理后, S1和S2桑叶茶中色氨酸含量显著提 升, 至8 h时, 分别为4.53和5.07 mg/g。厌氧对S1和S2桑叶茶中5-羟色胺的影响表现不同, S1中5-羟色胺含量在厌氧 初期(0~2 h)显著降低, 但随着厌氧时间延长逐渐回升且差异逐渐消失; S2中5-羟色胺含量显著提高, 厌氧处理8 h后 含量为100 ng/g。 【结论】高GABA含量桑叶茶类产品开发以鲜叶摊放1.5 h、揉捻30 min、真空厌氧处理8 h、干燥温度 80 °C的红茶型加工工艺为优, 所制得的桑叶茶香气呈甜香带花香, 滋味醇和, 汤色橙黄明亮。