Comparison of characteristic components in tea-leaves fermented by Aspergillus pallidofulvus PT-3, Aspergillus sesamicola PT-4 and Penicillium manginii PT-5 using LC-MS metabolomics and HPLC analysis

Microbiota influenced quality formation of ripened Pu-erh tea. To understand the effect of each tea-derived fungal strain, tea-leaves were fermented by Aspergillus pallidofulvus PT-3 (ApaPT), Aspergillus sesamicola PT-4 (AsePT) and Penicillium manginii PT-5 (PmaPT), respectively. 14 Phenolic compounds, 3 purine alkaloids, 19 free amino acids and γ-aminobutyric acid contents were determined by HPLC and amino acid analyzer analysis. Additionally, UHPLC-Q-TOF/MS method was developed for LC-MS metabolomics analysis. Multivariate statistical analyses, such as PCA and HCA, exhibited that the chemical profile of PmaPT fermentation was similar to biocidal treatment, but had significant differences with ApaPT and AsePT fermentation. The differentiated metabolites (VIP > 1, p < 0.05 and FC > 1.50 or < 0.66) and one-way ANOVA revealed the impact of three fungal strains in tea-leaves fermentation. APaPT and AsePT contributed to biosynthesis of gallic acid and several flavonoids, such as kaempferol, quercetin and myricetin in the metabolism of phenolic compounds.

Correlation analysis between filamentous fungi and chemical compositions in a pu-erh type tea after a long-term storage

Storage environment caused the difference between Jinhua Pu-erh tea (JPT) and General Pu-erh tea. In this study, fungal flora and chemical compositions were analyzed. The results showed that storage environment caused significant (p < .05) differences of theaflavins (TF), theabrownins (TB), tea polyphenols (TP), and water-soluble sugars (WSS), and a highly significant (p < .01) difference of thearubigins (TR). Aspergillus niger, Aspergillus pallidofulvus, Aspergillus sesamicola, Penicillium manginii, and Aspergillus tamarii were isolated from Pu-erh teas and identified based on colony characteristics and ITS, β-tubulin, and calmodulin gene sequences, respectively. A. pallidofulvus, A. sesamicola, and P. manginii were dominant fungi in JPT and generated macroscopic yellow cleistothecia after a long-term storage. Correlation analysis showed that dominant fungi exhibited significantly (p < .05 or p < .01) positive or negative corrections with TF, TB, TP, WSS, TR, and gallic acid. This study revealed dominant fungi including A. pallidofulvus, A. sesamicola, and P. manginii and their effects on given chemical compositions.

Identification of Similar Chinese Congou Black Teas Using an Electronic Tongue Combined with Pattern Recognition

It is very difficult for humans to distinguish between two kinds of black tea obtained with similar processing technology. In this paper, an electronic tongue was used to discriminate samples of seven different grades of two types of Chinese Congou black tea. The type of black tea was identified by principal component analysis and discriminant analysis. The latter showed better results. The samples of the two types of black tea distributed on the two sides of the region graph were obtained from discriminant analysis, according to tea type. For grade discrimination, we determined grade prediction models for each tea type by partial least-squares analysis; the coefficients of determination of the prediction models were both above 0.95. Discriminant analysis separated each sample in region graph depending on its grade and displayed a classification accuracy of 98.20% by cross-validation. The back-propagation neural network showed that the grade prediction accuracy for all samples was 95.00%. Discriminant analysis could successfully distinguish tea types and grades. As a complement, the models of the biochemical components of tea and electronic tongue by support vector machine showed good prediction results. Therefore, the electronic tongue is a useful tool for Congou black tea classification.

Comparison of Potent Odorants in Raw and Ripened Pu-Erh Tea Infusions Based on Odor Activity Value Calculation and Multivariate Analysis: Understanding the Role of Pile Fermentation

Infusions prepared from raw pu-erh tea (RAPT) and ripened pu-erh tea (RIPT) showed remarkable aroma differences. Predominant odorants in RAPT and RIPT infusions were identified and compared by the combined use of gas chromatography-olfactometry, aroma extract dilution analysis, odor activity values (OAVs), and multivariate analysis. A total of 35 and 19 odorants (OAV > 1) were detected in RIPT and RAPT, respectively. Odorants in RAPT and RIPT are significantly different in both odor properties and aroma compound intensities. Overall, RAPT contained a complex variety of chemical classes with diverse odors and moderate odor intensities, while RIPT is dominated by structurally and organoleptically similar compounds with high potency. Specifically, stale and musty smelling methoxybenzenes contributed the most to RIPT, while floral-, sweet-, and woody-smelling terpene alcohols, terpene ketones, and phenolic compounds were the predominant odorants in RAPT. Orthogonal partial least squares discriminant analysis revealed that linalool, α-ionone, 1,2,4-trimethoxybenzene, 1,2,3-trimethoxy-5-methylbenzene, 1,2,3,4-tetramethoxybenzene, and 1,2,3-trimethoxybenzene underwent remarkable changes during pile fermentation and could be used as potential odor-active markers for RIPT and RAPT discrimination. The comprehensive aroma characterization of pu-erh tea and determination of the effect of pile fermentation on odorant alteration herein will provide guidance for pu-erh tea flavor quality control and evaluation.

Physicochemical Aspects and Sensory Profiles as Various Potential Factors for Comprehensive Quality Assessment of Nü-Er-Cha Produced from Rhamnus heterophylla Oliv

Nü-Er-Cha, produced from the leaves of Rhamnus heterophylla Oliv., is known as an herbal tea and used in the treatment of bleeding, irregular menstruation and dysentery. A method was developed for the quality assessment of herbal tea, Nü-Er-Cha, adopting physical parameters, chemical constituents and sensory profiles as various potential factors. Their inner relationship was mined by multivariate statistical analysis tools, and the three factors were integrated by a technique for order preference by a similarity to ideal solution (TOPSIS) approach to comprehensively analyze the characters of Nü-Er-Cha. Viscosity was also introduced to the physical parameter determination besides conductivity, pH and color. Seven common peaks of eight batches of Nü-Er-Cha were marked by a high performance liquid chromatography (HPLC) fingerprint. They were further identified by HPLC mass spectrometry/mass spectrometry (HPLC-MS/MS) as hydroxybenzoic acids and flavanol glycosides. Fifty trained members participated in the sensory evaluation. Significant correlations between total sensory scores and conductivity, viscosity as well as pH were observed, a relatively innovative result for the quality assessment of herbal teas. The common peaks, belonging to hydroxybenzoic acids and flavanol glycosides, were mainly related to the color of infusions and leaves. The result of the TOPSIS analysis showed that S3 and S4 ranked as the top two in the comprehensive quality assessment. This may be related to rhamnetin triglycoside with a galactose/glucose and two rhamnoses, which had a higher peak response in S3 and S4 than that in the other samples. The present study may contribute to a better understanding of the relationship regarding physical properties, chemical composition and sensory profiles, and it may supply ideas for the comprehensive quality assessment of the herbal tea Nü-Er-Cha.

Detection of bitterness and astringency of green tea with different taste by electronic nose and tongue

An electronic nose was used to evaluate the bitterness and astringency of green tea, and the possible application of the sensor was assessed for the evaluation of different tasting green tea samples. Three different grades of green tea were measured with the electronic nose and electronic tongue. The sensor array of the E-nose was optimized by correlation analysis. The relationship between the signal of the optimized sensor array and the bitterness and astringency of green tea was developed using multiple linear regression (MLR), partial least squares regression (PLSR), and back propagation neural network (BPNN). BPNN is a multilayer feedforward neural network trained by an error propagation algorithm. The results showed that the BPNN model possessed good ability to predict the bitterness and astringency of green tea, with high correlation coefficients (R = 0.98 for bitterness and R = 0.96 for astringency) and relatively lower root mean square errors (RMSE) (0.25 for bitterness and 0.32 for astringency) for the calibration set. The R value is 0.92 and 0.87, and the RMSE is 0.34 and 0.55, for bitterness and astringency, respectively, of the prediction set. These results indicate that the electronic nose could be used as a feasible and reliable method to evaluate the taste of green tea. These results can provide a theoretical reference for rapid detection of the bitter and astringent taste of green tea using volatile odor information.

High-theabrownins instant dark tea product by Aspergillus niger via submerged fermentation: α-glucosidase and pancreatic lipase inhibition and antioxidant activity

BACKGROUND

Theabrownins (TB) are bioactive components that are usually extracted from Chinese dark tea, in which they are present at low concentrations. The present study aimed to produce an instant dark tea high in theabrownins via submerged fermentation by the fungus Aspergillus niger. Three fermentation parameters that affect theabrownins content (i.e. inoculum size, liquid-solid ratio and rotation speed) were optimized using response surface methodology.

RESULT

Optimum fermentation conditions were modeled to be an inoculum of 5.40% (v/v), a liquid-solid ratio of 27.45 mL g^-1 and a rotation speed of 184 rpm and were predicted to yield 292.99 g kg^-1 TB. Under these experimentally conditions, the TB content of the instant dark tea was 291.93 g kg^-1 . The antioxidant capacity and α-glucosidase and pancreatic lipase inhibitory activities of the high-TB instant black tea were higher than four other typical instant dark tea products.

CONCLUSION

The results of the present study show that careful management of culture conditions can produce a dark tea high in theabrownins. Furthermore, high-theabrownins instant dark tea could serve as a source of bioactive products and be used in functional foods as an ingredient imparting antioxidant properties and the ability to inhibit pancreatic lipase and α-glucosidase. © 2017 Society of Chemical Industry.