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Changes in Phytochemicals and Determination of Optimum Fermentation Time During Black Tea Manufacturing

M. M. Rahman
Department of Food Engineering and Tea Technology, Shahjalal University of Science and Technology, Sylhet- 3114, Bangladesh

M. M. Hossain
Department of Food Engineering and Tea Technology, Shahjalal University of Science and Technology, Sylhet- 3114, Bangladesh

R. Das
Department of Food Engineering and Tea Technology, Shahjalal University of Science and Technology, Sylhet- 3114, Bangladesh

I. Ahmad
Department of Food Engineering and Tea Technology, Shahjalal University of Science and Technology, Sylhet- 3114, Bangladesh

Abstract/ Executive Summary:

Black tea processing consists of four steps, namely withering, CTC, fermentation and drying, while cup quality made tea mostly controlled by fermentation step. This study evaluated biochemical changes at different stages of black tea processing in Bangladesh and determined the optimum fermentation time. Samples were collected from different tea processing stages to measure major phytochemicals and time intervals during fermentation to measure theaflavins and thearubigins ratio. Caffeine content was the least susceptible to processing steps. Biochemical changes started at withering, cell maceration and enzymatic oxidation started at CTC processing, thus the major reduction in the reducing sugar (20.46 to 04.95 ppm), catechin (16.88 to 7.95 ppm) and polyphenol (42.30 to 30.73 ppm) occurred here. The significant changes appeared during fermentation when polyphenol content decreased from 44.66 to 18.23 and catechin from 17.41 to 03.98 ppm due to the breakdown of these compounds to theaflavins (TF) and thearubigins (TR). The TF and TR ratio increased with fermentation time, and the highest of 1:8.4 was found at 50 min, which turned into 1:10 in the final product. The made tea quality parameters were comparable or better at fermentation time of 50 min than the quality of the black tea available in market.

Keywords: Tea processing; Fermentation or oxidation; Theaflavins, Thearubigins; Fermentation time

Location: Laboratory of Food Engineering and Tea Technology department, Shahjalal University of Science and Technology, Sylhet, Bangladesh

Start Date: 00-07-2015

End Date: 00-10-2015

Program Area: Postharvest and Agro-processing

Commodity: Tea

Objectives:

The objectives of this study were; (1) to measure the proximate and phytochemicals change to occur at different stages during tea processing and (2) to determine the optimum fermentation time by analyzing the TF: TR and different quality parameters.

Methodology:

Samples were collected from a tea factory of Sylhet, Bangladesh during the period of July –October 2015. The samples, namely fresh leaves, withered leaves, CTC rolled leaves, fermented leaves, and dried leaves or made tea, were taken at five different stages of the tea manufacturing process. The chemical analyses were started immediately after collection in the FET laboratory of Food Engineering and Tea Technology department, Shahjalal University of Science and Technology, Sylhet, Bangladesh. All the chemicals and reagents were used in the experiments were analytical grade. After collecting the sample, moisture and lipid content were measured. Then one gram sample was ground and mixed with 100 % ethyl alcohol, followed by filtered to take out 50 mL of ethyl alcohol extract. This alcoholic extract was used for subsequent analysis. Reducing sugar (dextrose equivalents) was extracted with alcohol. Ice cold acidified anthrone reagent (0.2 %, w/v) was added in the time of boiling for 8 min, and absorbance was taken at 630 nm. The total polyphenols content was determined by FolinCiocalteu’s reagent method. Chlorophyll a, b, and carotenoids were measured at the wavelength of 470, 653, and 666 nm, respectively, using UV-Visible spectrophotometer. To determine the Catechin content, 2 mL alcoholic extract of the sample was added to 6.5 mL of ice-cold vanilla (1% vanillin in 70% sulfuric acid), and absorbance was measured at 510 nm. In addition, caffeine was extracted with chloroform after boiling 5g sample with 30 mL water and 2g sodium carbonate for 10 min. The filtered supernatant was mixed with 20mL of distilled water and 10mL of chloroform, where chloroform was evaporated with a steam bath, and the weight of caffeine was recorded. Two types of fermentation have been practiced in the tea industry of Bangladesh for the production of CTC black tea. In this case study, samples had been collected from the method of floor fermentation. For the optimization of the quality parameters of CTC black tea, TF and TR ratio measurement was taken at 10 min interval starting from 10 to 40 min of fermentation residence time. After the 40th min of observation, the time interval was down to 5 min to get accurate TF: TR ratio and apposite residence time. Both theaflavin and thearubigin were determined using the method described in these reports with some modifications. Two grams of sample was added to 100 mL water and went to the filtration after infusing over the boiling water bath for 10 min. Solvent extraction of tea extract was carried out in separating funnels with adequate shaking at every stage, and contents of TF, TR, HPS and TLC were calculated from the absorbance values. Color index (CI) was derived using the formula, CI = (TF * 100) / (TR + HPS). All analyses were performed in triplicates, and the results were generated in this experiment were analyzed using SPSS Software Version 12. Analysis of variance (ANOVA) was done to measure the effect of treatments on proximate, phytochemicals, and quality parameters (TF: TR, HPS, TC, CI), and means were separated by the least significant difference (LSD) test at P < 0.05.

Source of Information: J. Sci. Res. 12 (4), 657-664 (2020)

Article Link (Online Journal): DOI: https://doi.org/10.3329/jsr.v12i4.45452

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The significant biochemical changes started in the stage of the withering and CTC process during black tea manufacture, and major changes took place during fermentation (oxidation). Polyphenol and catechin are two major compounds that decreased significant amounts by CTC and fermentation to produce theaflavins (TFs), thearubigins (TRs), high polymerized substance (HPS), total liquor color (TLC) and color index (CI). The ratio of TFs and TRs depends on the duration of fermentation. TFs and TRs ratio increased with increasing fermentation time, and 50 min of fermentation gave the highest TFs and TRs ratio, which also, in turn, came out as the highest TFs and TRs ratio of approximately 1:10 in the final product or black tea. The final product made from this fermentation gave comparatively better cup quality than that of the available tea in the market. As environmental temperature and humidity changes with seasonal change, further study on fermentation time during different tea processing season is recommended.

Knowledge Management: Journal