Changes undergone by free amino-acids during the manufacture of black tea

Chemical Composition of Kombucha

Kombucha is a fermented sweetened tea with a mixed fermenting culture of yeast and acetic acid bacteria. While the history of kombucha is not completely clear, it is now available around the world and has shown an increase in availability and demand in the United States market. The proponents of kombucha consumption tout the varied health benefits it can provide. The final kombucha flavor and composition is a function of both the initial tea used and the fermentation process. While the ascribed benefits are varied and numerous, the number of direct studies has been limited. This review focuses on the current state of understanding of the chemical composition and the potential health effects both positive and negative reported in the literature.

Changes in major catechins, caffeine, and antioxidant activity during CTC processing of black tea from North East India

Tea (Camellia sinensis L.) leaves undergo complex chemical transformations during black tea processing. However, the dynamic chemical changes during tea processing have not been explored in popular cultivars of North East India. In this study, changes in catechins, caffeine, total polyphenol (TP) and formation of theaflavins were examined throughout the different stages of CTC (curl, tear and crush) black tea processing based on UPLC metabolomic analysis along with antioxidant activity for eight cultivars viz. S.3A/3, TV1, TV7, TV9, TV17, TV22, TV23 and TV25. The results demonstrated that the most prolific changes were observed after complete maceration of tea leaves. The total catechin, (-)-epigallocatechin gallate and (-)-epicatechin gallate levels decreased by 96, 97 and 89%, respectively as the processing progressed from fresh leaves to black tea. The TP level decreased by 26 to 37% throughout the processing path. The caffeine content increased by 18% during processing. The total theaflavin reached the highest level at 20 min of fermentation and then decreased by 13 to 36% at 40 min. Cultivar TV23 and S.3A/3 had a high content of total theaflavin with 17.9 and 16.9 mg g-1, respectively. The antioxidant activity was observed to be decreased by 31% for the black tea as compared to fresh leaves. It is also observed that the total phenolic content exerted a greater effect on antioxidant activity rather than catechins and theaflavins. This study provides an insightful observation of black tea processing which will immensely help in improving the quality of processed tea.

Enzymatic Reaction-Related Protein Degradation and Proteinaceous Amino Acid Metabolism during the Black Tea (Camellia sinensis) Manufacturing Process

Amino acids contribute to the nutritional value and quality of black tea. Fermentation is the most important stage of the black tea manufacturing process. In this study, we investigated protein degradation and proteinaceous amino acid metabolism associated with enzymatic reactions during fermentation in the black tea manufacturing process. The results showed that the concentrations of both protein and free amino acids decreased during fermentation. We also confirmed that proteins were broken down into free amino acids by artificially synthesized dipeptide benzyloxycarbonyl glutamyl-tyrosine (Z-Glu-Tyr). Metabolites of the amino acid metabolic pathway increased significantly during fermentation. Furthermore, we confirmed that free amino acids were degraded to volatile compounds in a tracer experiment with the isotope precursor. These results provide information that will help black tea manufacturers improve the quality of black tea.

Rapid prediction of yellow tea free amino acids with hyperspectral images

Free amino acids are an important indicator of the freshness of yellow tea. This study investigated a novel procedure for predicting the free amino acid (FAA) concentration of yellow tea. It was developed based on the combined spectral and textural features from hyperspectral images. For the purposes of exploration and comparison, hyperspectral images of yellow tea (150 samples) were captured and analyzed. The raw spectra were preprocessed with Savitzky-Golay (SG) smoothing. To reduce the dimension of spectral data, five feature wavelengths were extracted using the successive projections algorithm (SPA). Five textural features (angular second moment, entropy, contrast, correlation, and homogeneity) were extracted as textural variables from the characteristic grayscale images of the five characteristic wavelengths using the gray-level co-occurrence matrix (GLCM). The FAA content prediction model with different variables was established by a genetic algorithm-support vector regression (GA-SVR) algorithm. The results showed that better prediction results were obtained by combining the feature wavelengths and textural variables. Compared with other data, this prediction result was still very satisfactory in the GA-SVR model, indicating that data fusion was an effective way to enhance hyperspectral imaging ability for the determination of free amino acid values in yellow tea.

CsGOGAT Is Important in Dynamic Changes of Theanine Content in Postharvest Tea Plant Leaves under Different Temperature and Shading Spreadings

We analyzed the changes of theanine content in postharvest tea leaves under high temperature (38 °C), low temperature (4 °C), and shading spreadings by using ultrahigh-performance liquid chromatography. The differentially expressed proteins (DEPs), CsFd-GOGAT and CsNADH-GOGAT, which are involved in theanine biosynthesis pathway, were identified from the corresponding proteome data. The protein-protein interactions of CsFd-GOGAT and CsNADH-GOGAT, CsTS1, or CsNiR were verified by yeast two-hybrid technology. The expression profiles of 17 genes in theanine metabolism, including CsFd-GOGAT and CsNADH-GOGAT, were analyzed by quantitative real-time polymerase chain reaction. The correlations between the dynamic changes of theanine content and expression profiles of related genes and DEPs were analyzed. This study preliminarily proved the importance of CsGOGAT in dynamic changes of theanine content in postharvest tea leaves during spreading.

Metabolic profiles from two different breakfast meals characterized by 1H NMR-based metabolomics

It is challenging to measure dietary exposure with techniques that are both accurate and applicable to free-living individuals. We performed a cross-over intervention, with 24 healthy individuals, to capture the acute metabolic response of a cereal breakfast (CB) and an egg and ham breakfast (EHB). Fasting and postprandial urine samples were analyzed using ¹H nuclear magnetic resonance (NMR) spectroscopy and multivariate data analysis. Metabolic profiles were distinguished in relation to ingestion of either CB or EHB. Phosphocreatine/creatine and citrate were identified at higher concentrations after consumption of EHB. Beverage consumption (i.e., tea or coffee) could clearly be seen in the data. 2-furoylglycine and 5-hydroxymethyl-2-furoic acid - potential biomarkers for coffee consumption were identified at higher concentrations in coffee drinkers. Thus ¹H NMR urine metabolomics is applicable in the characterization of acute metabolic fingerprints from meal consumption and in the identification of metabolites that may serve as potential biomarkers.

Non-targeted analysis by LC-MS of major metabolite changes during the oolong tea manufacturing in New Zealand

Oolong tea is a semi-fermented tea that is partially oxidised during the manufacturing process to create a product unique in composition. In this study, we investigated the potential of non-targeted LC-MS with two complementary chromatographic modes to provide a "comprehensive and unbiased" view of biochemical compositional changes occurring during oolong tea manufacturing in New Zealand. Tea leaf samples from throughout the manufacturing/fermentation process during three different harvest periods (spring, summer and autumn) were analysed by four different LC-MS streams. Principal component analysis revealed the de-greening stage of the manufacturing process was responsible for major changes in the biochemical profile, with the methodology detecting changes in a wide range of metabolites of differing polarities, such as flavonoids, nucleosides and primeverosides. Changes during the fermentation phase of the manufacturing process were less marked, however significant increases in levels of free amino acids, a hydroxyjasmonic acid and related metabolites were observed.

Chemistry of secondary polyphenols produced during processing of tea and selected foods

This review will discuss recent progress in the chemistry of secondary polyphenols produced during food processing. The production mechanism of the secondary polyphenols in black tea, whisky, cinnamon, and persimmon fruits will be introduced. In the process of black tea production, tea leaf catechins are enzymatically oxidized to yield a complex mixture of oxidation products, including theaflavins and thearubigins. Despite the importance of the beverage, most of the chemical constituents have not yet been confirmed due to the complexity of the mixture. However, the reaction mechanisms at the initial stages of catechin oxidation are explained by simple quinone-phenol coupling reactions. In vitro model experiments indicated the presence of interesting regio- and stereoselective reactions. Recent results on the reaction mechanisms will be introduced. During the aging of whisky in oak wood barrels, ellagitannins originating from oak wood are oxidized and react with ethanol to give characteristic secondary ellagitannins. The major part of the cinnamon procyanidins is polymerized by copolymerization with cinnamaldehyde. In addition, anthocyanidin structural units are generated in the polymer molecules by oxidation which accounts for the reddish coloration of the cinnamon extract. This reaction is related to the insolubilization of proanthocyanidins in persimmon fruits by condensation with acetaldehyde. In addition to oxidation, the reaction of polyphenols with aldehydes may be important in food processing.

Chromatography of tea constituents

Modern chromatographic techniques such as high-performance liquid chromatography are currently the most helpful approach to the routine analysis of and research of non-volatile tea constituents. Using these techniques some errors in the more classical analytical techniques could be detected. Unfortunately, some of these methods of analysis are still in widespread use, even as official methods. However, knowledge of especially the polyphenols in tea is still lacking, and for many of the minor polyphenols no chromatographic methods for the determination exist.

Metabolism of methionine and biosynthesis of caffeine in the tea plant (Camellia sinensis L.)

1. Caffeine biosynthesis was studied by following the incorporation of 14C into the products of L-[Me-14C]methionine metabolism in tea shoot tips. 2. After administration of a 'pulse' of L-[Me-14C]methionine, almost all of the L-[Me-14C]methionine supplied disappeared within 1 h, and 14C-labelled caffeine synthesis increased throughout the experimental periods, whereas the radioactivities of an unknown compound and theobromine were highest at 3 h after the uptake of L-[Me-14C]methionine, followed by a steady decrease. There was also slight incorporation of the label into 7-methylxanthine, serine, glutamate and aspartate, disappearing by 36 h after the absorption of L-[Me-14C]methionine. 3. The radioactivities of nucleic acids derived from L-[Me-14C]methionine increased rapidly during the first 12 h incubation period and then decreased steadily. Sedimentation analysis of nucleic acids by sucrose-gradient centrifugation showed that methylation of nucleic acids in tea shoot tips occurred mainly in the tRNA fraction. The main product among the methylated bases in tea shoot tips was identified as 1-methyladenine. 4. The results indicated that the purine ring in caffeine is derived from the purine nucleotides in the nucleotide pool rather than in nucleic acids. A metabolic scheme to show the production of caffeine and related methylxanthines from the nucleotides in tea plants is discussed.

Metabolism of methylamine in the tea plant (Thea sinensis L.)

1. The metabolism of methylamine in excised shoot tips of tea was studied with micromolar amounts of [(14)C]methylamine. Of the [(14)C]methylamine supplied 57% was utilized by tea shoots during the 10h experimental period. 2. The main products of [(14)C]methylamine metabolism in tea shoots were serine, gamma-glutamylmethylamide, theobromine, caffeine and CO(2). There was also incorporation of the label into glutamate, aspartate, RNA purine nucleotides and S-adenosylmethionine. 3. The formation of methylamine from gamma-glutamylmethylamide was confirmed by feeding tea shoots with gamma-glutamyl[(14)C]methylamide. The products of gamma-glutamyl[(14)C]methylamide metabolism in tea plants were serine, theobromine, caffeine, glutamate and aspartate. 4. The results indicate that the oxidation of methylamine to formaldehyde is the first step of methylamine utilization. Labelled formaldehyde released by the metabolism of methylamine leads to the incorporation of the label into metabolites on the C(1) pathways of this compound. It is also suggested that formaldehyde is further oxidized via formate to CO(2). 5. The role of gamma-glutamylmethylamide in methylamine metabolism in tea plants is discussed. 6. Results support the view that theobromine is the immediate precursor of caffeine.

Studies on the ribonucleic acids of fresh and processed tea leaves

1. A marked decrease in the total RNA content during the withering process of tea leaves was found. During the fermentation process, there was a small but significant decrease in the total RNA content. 2. During isolation of RNA from tea leaf tissues, the action of leaf ribonuclease was minimized by the addition of sodium dodecyl sulphate during extraction; 1% (w/v) sodium dodecyl sulphate in 0.2m-tris-hydrochloric acid buffer, pH8.0, containing 0.005% EDTA was found to be most efficient for the extraction and gave about 93% yield. 3. The total RNA preparations isolated from fresh, withered and fermented tea leaves were compared with regard to nucleotide composition and spectral characteristics. The total RNA preparations from all three sources contained more purines than pyrimidines (purine/pyrimidine ratio 1.47-1.52).