Analysis Of The Microbial Assemblages In A Local Fermented Tea Product

Abstract

Fermented tea has been widely consumed by many countries and may be a promising product in Vietnam. Thus, it can generate additional incomes for tea growers. However, locally fermented tea is not well studied. Therefore, the objectives of this study are to evaluate some basic quality parameters of a locally fermented tea product (with different fermentation times: 2 and 5 years) and compare them with that of non-fermented tea (green tea grown in Ha Giang province, material of the fermented tea). Apart from this, the study also analyzed the microbial communities in these tea samples. Total polyphenol content and free radical scavenging capacity of tea samples, which are among the important criteria for tea qualification, were determined by Folin-Ciocalteu assay and DPPH assay. The microbial communities of the tea sample were isolated by serial dilution and spread plate method. Then, they were morphologically and molecularly identified. The total polyphenol content in the green tea (24.98±1.64 mg/g) was significantly higher than in 2-year fermented tea (22.99±0.94 mg/g) and 5-year fermented tea (16.15±0.57 mg/g). The DPPH radical scavenging capacities were also recorded with the same trend, with the IC50 values of 284.82±3.10µg/ml, 296.15±2.61µg/ml and 335.03±2.80 µg/ml for green tea, 2-year and 5-year fermented tea. These suggest that the total polyphenol contents and DPPH scavenging abilities of tea samples were significantly reduced during and over fermentation. Molds and bacteria were found in all 3 samples, with 5-year fermented tea having the most species and number of microbes. Molecular identification revealed microbes in 5-year fermented tea, which were Bacillus cereus (1.13×104 CFU/g), Peribacillus frigoritolerans (4.0×102 CFU/g), Bacillus amyloliquefaciens (2.0×102 CFU/g), Aspergillus pseudoglaucus (1.32×103 CFU/g), Aspergillus ruber (1.48×103 CFU/g), Aspergillus cibarius (1.10×103 CFU/g) and Aspergillus restrictus (2.35×104 CFU/g). Meanwhile, as the densities of microbes in 2-year fermented tea and green tea were relatively low, they were only identified by morphological characteristics. Based on their morphologies, the bacteria and fungi from these two samples were putatively identified as Bacillus spp., Aspergillus sp and Mycelia sterilia. In 2-year fermented tea, there were one Bacillus sp. (50 CFU/g), and one Aspergillus sp. (100 CFU/g). Four Bacillus spp. and one Mycelia sterilia were found in green tea with the densities were mostly about 50 to 150 CFU/g. Based on the identification, the fungal and bacterial communities and densities were specific to each tea sample.