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

【Objective】To investigate the effects of anaerobic time on the main mulberry leaf tea components such asγ-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 ℃. 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.