The effects of fermentation conditions (temperature, time, and pH) and plucking standards (one leaf and a bud to four leaves and a bud) on the chemical components and sensory quality of the fermented juices processed from crushed fresh tea leaves were investigated. The results showed that optimum fermentation conditions that resulted in fermented juices of the best sensory quality and the highest content of TFs were a temperature of 35°C, time duration of 75 min, and pH 5.1. The fermented juices processed from new shoots with three leaves and a bud or four leaves and a bud afforded high overall acceptability and TF concentration. These differences arise because tea leaves with different plucking standards have different catechin content and enzyme activities. Fermented tea juice possessed higher concentrations of chemical components such as soluble solids, amino acids, and TFs and exhibited better sensory quality as compared to black tea infusion. The TF concentrations decreased as the pH of the fermenting juice increased, and the fermented juice showed the best overall acceptability. These results provide essential information for the improvement of the processing of black tea beverage by suggesting fermentation of fresh tea leaves as a better alternative to their infusion.
Tea is one of the most popular beverages in the world. It is rich in antioxidants that help prevent various ailments such as cancer and heart diseases [
Fermentation is a critical stage in the manufacturing of black tea during which catechins are oxidized to TFs and TRs by the action of polyphenol oxidase (PPO) and peroxidase (POD) enzymes [
In China, the consumption of black tea beverage accounted for more than 40% of the total amount (14 million tons) of tea beverage produced in 2011 [
Fresh shoots (including one leaf and a bud (mono-leaf), two leaves and a bud (di-leaves), three leaves and a bud (tri-leaves), and four leaves and a bud (quad-leaves)) from tea plants (
The plucked fresh tea shoots were loaded in a withering trough at the rate of 6 kg·m−2. Ambient air was passed through the leaves for 14 h to bring about appropriate physical and chemical withering. The withered leaves (600 g), with 62% water content (
Analyses of catechins, caffeine, gallic acid, and TFs were performed by HPLC [
TRs were determined using the method described by Roberts and Smith [
Fresh tea leaves (0.5 g) were homogenized in 10 mL of 0.05 M phosphate buffer and 0.3 g of polyvinyl polypyrrolidone (PVPP) using a mortar and pestle at 4°C. The homogenate was left to extract at 4°C for 12 h and then centrifuged at 19000
Fermented juices were scored by a professional team of ten experts in tea quality evaluation from the Tea Research Institute of the Chinese Academy of Agricultural Sciences. The taste and colour of the fermented juices were scored by each member of the team. The nine-point hedonic scale was used (9 = extreme like, 5 = neutral, 1 = extreme dislike) for scoring. The scores of the taste and colour were integrated into the acceptability score [
Results are expressed as a mean of three replicates. Analysis of variance and significant differences among means were performed with one-way ANOVA using SPSS 16.5 (IBM, Armonk, NY). Correlation analysis was also performed using SPSS 16.5.
During fermentation, catechins are oxidized to
Effect of fermentation time and temperature on the concentrations of (a) theaflavins, (b) thearubigins, (c) catechins, and (d) the overall acceptability of fermented juices (
Increasing the fermentation temperature can increase the rate of enzymatic oxidation which may lead to a faster depletion of all catechins. During fermentation, the concentrations of catechins in fermented juice gradually decreased (Figure
The formation of TRs was also found to be influenced by the fermentation temperature and time (Figure
Figure
The pH value may be an important factor that influences the formation of TFs during the fermentation process. Cloughley and Ellis [
Effect of pH on the concentrations of different chemical components (mg·mL−1) and overall acceptability of fermented juices.
pH | Overall acceptability score | Gallic acid | Caffeine | Amino acids | Catechins | TFs | TRs |
---|---|---|---|---|---|---|---|
4.3 | 5.73a | 0.13a | 0.87a | 0.62b | 1.21a | 0.24a | 0.92a |
4.7 | 5.88a | 0.17b | 0.88a | 0.57c | 1.17a | 0.21b | 0.96a |
5.1 | 6.86b | 0.17b | 0.89a | 0.52d | 0.91b | 0.18c | 1.21b |
5.5 | 6.51c | 0.24c | 0.98b | 0.66a | 0.85c | 0.16d | 1.42c |
a,b,c,dSignificant differences at the level
Fresh tea leaves with different plucking standards were fermented in order to evaluate their effect on the contents of chemical components and sensory quality of fermented juice. Table
Overall acceptability and the concentrations of different chemical components (mg·mL−1) of the fermented juices derived from fresh tea leaves with different plucking standards.
Tea leaves | Overall acceptability score | Caffeine | Amino acids | Catechins | TFs | TR |
---|---|---|---|---|---|---|
Mono-leaf | 6.48a | 0.60a | 0.52a | 0.91a | 0.136a | 1.39a |
Di-leaves | 6.69b | 0.55b | 0.47b | 0.90a | 0.127a | 1.20b |
Tri-leaves | 7.87c | 0.47c | 0.41c | 0.86b | 0.206b | 1.70c |
Quad-leaves | 7.79c | 0.41d | 0.43c | 0.77c | 0.211b | 1.75c |
a,b,c,dSignificant differences at the level
TFs are the components of black tea infusion that have a significant influence on the quality of black tea [
Effect of the plucking standard of fresh tea leaves on the TF concentrations of fermented juices (
Content of catechins (%) in fresh tea leaves with different plucking standards.
Tea leaves | EGC | EGCG | EC | ECG | Total catechins |
---|---|---|---|---|---|
Mono-leaf | 0.95a | 4.84a | 0.38a | 0.68a | 8.46a |
Di-leaves | 1.24b | 3.84b | 0.42b | 0.52b | 7.24b |
Tri-leaves | 1.34c | 3.46c | 0.44c | 0.46c | 6.88c |
Quad-leaves | 1.60d | 3.18d | 0.41b | 0.43d | 6.17d |
a,b,c,dSignificant differences at the level
During fermentation, catechins are oxidized by PPO and POD to form TFs and TRs [
PPO and POD activities of fresh tea leaves with different plucking standards (
The present study investigated the effect of fermentation conditions and the plucking standard of fresh tea leaves on the chemical components and sensory quality of fermented juice. On the basis of the analyses of the chemical components and the overall acceptability of fermented juices, the optimum parameters for the fermentation process were determined to be a temperature of 35°C, time duration of 75 min, and pH 5.1. One bud and three leaves (tri-leaves) and one bud and four leaves (quad-leaves) were better materials for the production of fermented juice than one bud and one leaf (mono-leaf) and one bud and two leaves (di-leaves). These results provide the practical information for processing fermented tea juice, which is used for the production of black tea beverage by fermentation of fresh tea leaves. Tea processors can process fermented juice with higher TFs and better sensory quality than black tea processed with conventional methods.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
Ping Tang and Dan-Yu Shen contributed equally to this work.
This research was supported by the Hangzhou Agricultural Scientific Research Project (20160432B25) and the Central Level, Scientific Research Institutes for Basic R&D Special Fund Business (Y2016PT40 and Y2016CG13).