Tea Samples Research Articles

Optimization and test of the heating parts of gas-fired tea fixation and shaping machine

IntroductionThe uneven heating of the U-shaped multi-groove pot in gas-fired tea fixation and shaping machines results in inconsistent quality of tea leaves.MethodsA three-dimensional model of the gas-fired tea fixation and shaping machine was established by using SOLIDWORKS software. With the use of ANSYS finite element software, the orthogonal experiment method was applied to analyze and optimize the design of the spacing arrangement, the shape of the heating parts, and the heat conduction temperature field.ResultsResults show that the optimized heating parts significantly reduce the temperature difference on the surface of the U-shaped multi-groove pot, and the surface temperature field of the multi-groove pot is more uniform, which greatly improves the efficiency and quality of fresh tea leaf fixation and shaping. Prototype temperature and tea sample fixation ratio tests verified that the optimized heating components significantly improved the temperature uniformity of the U-shaped multi-groove pot and the quality of the finished tea.DiscussionThe research findings provide insights for further improving the uniformity of the U-shaped multi-groove pot’s temperature in the tea fixation and shaping machine.

Characteristic volatile compounds of white tea with different storage times using E-nose, HS-GC-IMS, and HS-SPME-GC-MS.

This paper studied the influence of storage duration on the flavor profile of white tea in detail, with samples produced between 2020 and 2023. Sensory evaluation was performed by quantitative descriptive analysis (QDA), followed by an in-depth aroma components analysis employing an electronic nose (E-nose), headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS), and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). The QDA findings revealed a gradual transition in the flavor profile of white tea during storage, shifting from sweet, fruity, and floral to more herbal and stale characteristics. E-nose could well distinguish white tea with different storage times. A total of 55 and 53 volatile compounds were identified by HS-GC-IMS and HS-SPME-GC-MS, respectively. The orthogonal partial least squares-discriminant analysis models, based on HS-GC-IMS (R2Y=0.998, Q2=0.987) and HS-SPME-GC-MS (R2Y=0.984, Q2=0.993), successfully distinguished white tea samples stored for different storage times. Furthermore, 14 and 8 key compounds were screened based on the double variable criterion of one-way analysis of variance (p<0.05) and variable importance in projection (VIP) >1.2, and their content changes were also compared. It is the gradual decrease of important aroma components such as 2-hexenal, 2-methyl-2-hepten-6-one, linalool, and geraniol, which are positively correlated with sweet, fruity, and floral aromas, and the gradual increase of hexanoic acid, thiophene, propanoic acid, dimethyl disulfide, and borneyl acetate, which are positively correlated with herbal and stale flavor, that leads to the changes in flavor and aroma of white tea during storage. The results of the study provided a reference for elucidating the aroma characteristics of white tea at different storage times as well as a theoretical basis for the quality control of white tea.

Electrochemical Detection and Characterization of Caffeine in Selected Tea Samples using Polyglycine Modified Carbon Paste Electrode

Glycine was electro-polymerized against a carbon paste electrode (CPE) to produce a polymer film via the electro-oxidation process comprising amino (-NH2) and carboxylic (-COOH) groups, by a cyclic voltammetric. The electrochemical oxidation of caffeine was examined in 0.2 M phosphate buffer solution (PBS). The Polyglycine modified Carbon Paste Electrode (PGMCPE) demonstrates greater electrocatalytic activity for caffeine as compared to the unmodified CPE (UNMCPE). This made it suitable for analyzing caffeine owing to its increased electrode surface area and/or improved electron transport at the electrode surface. By varying the concentration range from 0.05 to 0.9 mM, the relationship between peak current and caffeine concentration was studied and this produced a correlation coefficient of R2 = 0.9987. This method was extremely capable of evaluating caffeine concentrations. Square wave voltammetry (SWV) was utilized to assess the caffeine in tea samples. The sample was analyzed with square wave voltammetry and was made easier with an ideal pH of 12.0. Additionally, the caffeine levels in a tea sample were successfully measured using the linear range and detection limit, and the results showed a good limit of detection (LOD) in comparison to previous literature.

Synthesis and nanoparticle formation of pyrazine, benzodithiophene (BDT) and fluorene containing conjugated polymer (P-PBF) and its biosensing performance toward catechol

The development of laccase-based biosensors, in particular, have attracted much interest due to their ability to detect highly toxic molecules in the environment. This article reports a novel biosensor for catechol detection that can be used to determine toxic molecules in the environment. For this purpose, a novel conjugated polymer (P-PBF) and conjugated polymer nanoparticles (P-PBFNPs) were synthesized and characterized, respectively. To our knowledge, research has yet to be done on conjugated polymer nanoparticle-based electrochemical biosensing platforms for catechol determination. The biosensor comprises a GE/P-PBF NPs/Lac electrode, constructed with P-PBF NPs deposited onto a bare graphite electrode followed by laccase (Lac) enzyme immobilization. While electrochemical characterization was performed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), surface characterization was performed by field emission scanning electron microscopy (FE-SEM). The biosensor exhibited high sensitivity (1.229 μA/μM.cm2), a good linear range (0.5–25 μM) and a low limit of detection (LOD) (0.49 μM). Moreover, the developed biosensor exhibited high selectivity in the presence of interfering analytes without any memory effects. The potential of the GE/P-PBF NPs/Lac electrode in tap water, green tea, synthetic urine and serum samples indicates the inspiring biosensing applications for monitoring environmental pollution.

Gadolinium oxide modified molecular imprinted polymer electrode for the electrochemical detection of theophylline in black tea

The present study reported a facile approach to fabricate a molecular imprinted polymer electrode modified with nano-composites of gadolinium oxide (Gd2O3@TH-MIP-CPE) to detect theophylline in variants of black tea samples. The synthesized electrode material was characterized by scanning electron microscope, fourier transform infrared spectroscopy and UV–visible spectroscopy. The electroanalytic performance of the Gd2O3@TH-MIP-CPE electrode was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The electrode exhibits a linear response from 50 µM to 900 µM with limit of detection being 2.004 µM. The electrode showed significant repeatability (%RSD=1.19), reproducibility (%RSD=0.92) and stability (%RSD=1.015). To evaluate the predictive ability of the electrode, partial least square regression (PLSR) model has been developed by correlating the high-performance liquid chromatography (HPLC) values with the voltammogram signals recorded using the electrode. The average prediction accuracy obtained from the PLSR model is 91.3 % with root mean square error of calibration being as low as 0.73.

HS-SPME-GC-MS combined with relative odor activity value identify the key aroma components of flowery and fruity aroma in different types of GABA tea

Anaerobic processing is a crucial factor influencing the formation of flavor quality in Gamma-aminobutyric acid (GABA) tea. In this study, headspace solid-phase microextraction combined with gas chromatography and mass spectrometry was employed to explore the flavor characteristics of different types of GABA tea. We utilized multivariate analyses to identify at least 146 volatile components (VOCs) across 12 functional groups in the GABA tea samples via principal component analysis (PCA). At least 40 differential VOCs were screened from the GABA tea samples via orthogonal partial least squares-discriminant analysis. Subsequently, a minimum of four VOCs were identified in the GABA tea samples via the Pearson correlation coefficient combined with relative odor activity values as potential markers for flowery and fruity aromas, clarifying the impact of the VOCs on these characteristics. The results of this study provide a theoretical basis for understanding the formation of flowery and fruity flavor characteristics in GABA tea.

Continuous step-wise temperature extraction improves the flavanol content of tea beverages.

Tea is the second most consumed beverage worldwide and its health benefits have been extensively studied because of its rich flavanol content. This study aims to evaluate the efficacy of a novel continuous step-wise temperature extraction process in maximising antioxidant activity, total phenolic content and flavanol concentration of different tea beverages. Continuous step-wise temperature extraction produced the highest absolute antioxidant capacity, total phenolic content and concentration of major tea flavanols in Yuhua tea compared to the other tea types at all extraction points. Despite having the lowest baseline concentration of tea flavanols, Lapsang Souchong tea showed the greatest increase in catechin and epigallocatechin-3-gallate levels with the continuous step-down temperature process, by over 500% and 300%, respectively. In addition, Moonlight White tea showed the greatest percentage change in total antioxidant capacity and phenolic content at the end of the process compared to the baseline. Furthermore, the continuous step-wise temperature extraction showed a moderate increase in caffeine concentration in all the tea samples. Our findings revealed a beneficial impact of continuous step-wise temperature extraction on the antioxidant capacity, phenolic content and flavanol profile in different types of tea, which may be valuable in the production of added-value tea beverages. © 2024 Society of Chemical Industry.

Acute change in resting energy expenditure and vital signs in response to white tea consumption in females: a pilot study

BackgroundWhite tea, derived from the Camellia sinensis plant like other teas, uses tender buds and young leaves and undergoes minimal processing. This results in higher levels of antioxidants and bioactive substances, which may enhance thermogenesis more effectively than other teas. This first human study aimed to investigate the acute effects of white tea consumption on resting energy expenditure (REE) and some vital signs, including blood pressure (BP), heart rate (HR), and body temperature (BT).MethodsThirty-two healthy female volunteers with normal initial BP and whose caffeine intakes were < 300 mg/d were enrolled in the study. The caffeine and total phenolic content of white tea samples were determined by the high-performance liquid chromatography method and the Folin-Ciocalteu colorimetric method, respectively. After baseline measurements, participants consumed white tea containing 6 mg of caffeine per kilogram of lean body mass, and the white tea was prepared with bottled drinking water at 80 °C and brewed for 3 min. REE, BP, and BT were assessed at various intervals (baseline, 30 min, 120 min, and 180 min) post-consumption of the white tea.ResultsThe results revealed a significant increase in REE by 8.7% at 180 min after the consumption. In particular, there was a substantial difference in both values between the intervals of 30 min to 180 min and baseline to 180 min for REE (p < 0.05). Maximal oxygen consumption and BT also increased significantly over time (p < 0.05) and the observed increment in BT suggests a thermogenic effect associated with white tea consumption. However, systolic BP, diastolic BP, and heart rate showed no significant difference.ConclusionsThese findings suggest white tea consumption may acutely enhance REE and maximal oxygen consumption, so the results are promising for body weight management. This study is the first human study in the literature about the effects of white tea on energy expenditure and vital signs.

Temporal analysis of non-targeted flavor component variation in green tea storage and rapid prediction of storage duration

The precise changes in the flavor quality of green tea before and after the optimal consumption period remain elusive. This study used HS-SPME-GC–MS to carefully examine the volatile compounds of green tea samples from multiple storage periods and simultaneously detected changes in taste and color during tea infusion. Notably, 16 compounds with VIP > 1.5 were identified, highlighting their significance in the overall analysis profile. Among these components, nonanoic acid, octanoic acid and hexanal were identified as potential contributors to off-flavors and rancid oil flavors in tea after storage. The color of the tea broth becomes darker. Bitter flavor is associated with increased amino acid content. The PSO-SVM model showed excellent accuracy for predicting the storage duration of green tea. These findings provide critical theoretical understandings of green tea manufacturing and quality control.

Identification of lu’an Guapian at different picking periods by using excitation–emission matrix fluorescence spectroscopy coupled with chemometrics

Lu’an Guapian (LAGP) is a renowned green tea, with its price significantly higher when picked before the Qingming Festival compared to after, posing risks of confusion and counterfeiting. This study proposed using an excitation-emission matrix (EEM) fluorescence method combined with chemometrics for rapid identification of tea picked before and after Qingming Festival. Firstly, the differences among the EEM fingerprints of different tea samples were analyzed using the alternating trilinear decomposition (ATLD) algorithm. To determine the differences between LAGP before and after Qingming Festival, the total contents of ten main components in tea were detected, and their effects on the EEM fluorescence fingerprint of tea were analyzed using correlation heatmaps. Finally, two chemometric algorithms, partial least squares discriminant analysis (PLS-DA) and k-nearest neighbor (k-NN), were used to classify LAGP before and after Qingming Festival, achieving a classification accuracy of 100% for the training set, test set, and prediction set. To further explore the potential of this method, LAGP was further classified in detail according to four detailed picking periods, achieving an accuracy of over 83%. The same chemometric algorithm was used to classify the data based on the high-performance liquid chromatography (HPLC) method, yielding results comparable to those of the EEM-based method, though slightly inferior. Variable importance projection (VIP) analysis shows that catechin analogs are the main contributors to the classification of LAGP. The results demonstrated the EEM method’s significant potential in identifying the picking time of green tea.

Determination of copper at trace levels in fennel tea samples by flame atomic absorption spectrometry after the implementation of simultaneous complexation and supramolecular solvent based spraying assisted liquid phase microextraction

A simple and efficient preconcentration method named as supramolecular solvent based spraying assisted liquid phase microextraction (SUPRAS-SA-LPME) was combined with a flame atomic absorption spectrometry (FAAS) for the determination of copper in fennel tea samples at trace levels. An alkanol (1-decanol)/THF based SUPRAS (containing complexation agent) was used as extraction solvent instead of traditional organic solvents for the first time in an SA-LPME process. Under the optimum conditions, system analytical performance of the developed method was evaluated, and limit of detection (LOD)/limit of quantitation (LOQ) values were recorded as 1.91/6.37 µg kg–1. After the evaluation of system analytical performances, the enhancement in detection power/calibration sensitivity was found to be 21.3/21.8 folds when the comparison of LOD values/calibration plot slopes of the FAAS and SUPRAS-SA-LPME-FAAS systems. The method applicability was tested for the fennel tea samples by spiking experiments, and acceptable recovery results (80.2 % – 111.8 %) were obtained for low, mid and high spiked concentration levels.

The preference mapping and the drivers of liking for ready-to-drink tea beverages

Abstract This study aims to investigate the preference mapping and drivers of liking for ready-to-drink tea (RTD) tea beverages. The RTD tea samples were selected based on the type (black, green, oolong) and different sugar additions (sweetened, unsweetened, less sweet). In addition, various flavored (jasmine, milk, fruity) teas were also included. A total of 12 RTD tea samples were evaluated using descriptive analysis by 14 trained panelists. In addition, the preferences of the RTD teas were investigated by 131 participants (mean age 24.0 ± 9.2, 45% men, 55% women). The results show that the sensory profiles of RTD tea were very diverse based on the ingredients such as type of tea, flavors, and sweetness levels. The acceptability indicated that sweetened and flavored RTD teas have a higher liking (p&lt; 0.05) compared to unsweetened and plain samples. The preference mapping shows that the overall liking for RTD tea was associated with sweet taste, sweet aroma, and sweet aftertaste while sensorial attributes of bitter taste, bitter aroma, astringent, burnt aroma, bitter aftertaste, and leafy aroma may influence consumers disliking. This study identifies factors that drive consumer preferences for RTD tea and provides insight for the development of RTD tea by maximizing sensorial properties.

The effects of varying ingredients combination and boiling time on total phenolic content, antioxidant activity, and antimicrobial properties of lemongrass-ginger tea

This study was aimed at exploring the effect of varying lemongrass-ginger combinations, and boiling time on total phenolic contents (TPC), antioxidant activity, and antimicrobial efficacy of lemongrass-ginger tea. Lemongrass-ginger tea was produced by varying the percentage of lemongrass (25 %, 50 %, and 75 %) and boiling times (5, 10, and 15 min). The antioxidant activity of the lemongrass-ginger tea samples was investigated using the DPPH and ABTS assays whereas the TPC was determined using the Folin-Ciocalteau method. The antimicrobial activities were investigated by measuring the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum fungicidal concentration (MFC) of the tea against selected microorganisms, and its combinatory effects with antimicrobial drugs. The lemongrass-ginger combination and the boiling time significantly affected antioxidant potential, TPC, and antimicrobial activities. TPC measured ranged between 966.7 ± 90.20 to 1761.3 ± 81.70 μgGAE/g whereas DPPH antioxidant activities varied from 43.97 ± 14.99 % to 75.20 ± 8.55 %. The highest values of TPC and DPPH were 1761.3 ± 81.70 μgGAE/g and 75.20 ± 8.55 % and were recorded by 75 % lemongrass-ginger combination boiled for 15 min. Furthermore, differences in lemongrass-ginger combination and boiling times resulted in varying antimicrobial activities against the test microorganisms. The lowest MBC was recorded for 50 % lemongrass boiled for 10 min against C. albicans, 75 % lemongrass boiled for 15 min against K. pneumoniae and S. typhi, and 25 % lemongrass against E. coli. Additionally, varying ingredient proportions and boiling times affected the combinatory effect of the tea with antimicrobial drugs. However, the exact effect depends on the proportion of ingredients used and the boiling times.

Combining non-targeted and targeted metabolomics to study key bitter and astringent substances of Liupao tea

Liupao tea is a post-fermented dark tea with bitterness and astringency as key sensory traits, though its chemical composition is not fully understood. Six Liupao tea samples with significant differences in bitterness and astringency were analyzed using non-targeted metabolomics and sensory evaluation. Thirty finished and five semi-finished Liupao tea samples were analyzed using UHPLC-MS-PRM for targeted quantification of bitter and astringent compounds. The results show that 477 non-volatile compounds were detected, including 18 potential bitter compounds and 22 potential astringent compounds. Six key bitter compounds (epigallocatechin gallate, catechin gallate, caffeine, quinic acid, neochlorogenic acid, and caffeic acid) and 11 key astringent compounds (e.g., epigallocatechin gallate, gallic acid, chlorogenic acid, ellagic acid) were identified. After fermentation, flavonoid glycosides and flavanols were reduced by 62.41 % to 97.46 %, while phenolic acids showed varied trends. Different rates of change in key compounds during fermentation resulted in variations in bitterness and astringency. This study offers insights for improving Liupao tea quality.

Unveil the molecular recognition mechanisms of triazine haptens and monoclonal antibodies: Establishing ic‐ELISA methods for triazine herbicide analysis in tea

AbstractThis study introduced two triazine haptens (with 0 or 1 carbon connecting arms at nonisopropyl positions) and developed two heterologous indirect competitive enzyme‐linked immunosorbent assay (ic‐ELISA) methods. The IC50 values for the 17 triazine pesticides ranged from 0.84 ng/mL to 225.63 ng/mL, and the established method was applied to determine their concentrations in tea samples. This study aimed to address the current debate on the recognition mechanism of triazine haptens with shorter connecting arms. This study produced two new findings by investigating the recognition mechanism of triazine haptens and antibodies. On the one hand, the specific amino acid isoleucine (ILE‐219) is crucial for isopropyl recognition. On the other hand, the selection of the connecting site of the triazine hapten has a significant effect on the specificity of the antibody, with the influence of the length of the carbon connecting arm being secondary. Our newly designed haptens show promise for diverse triazine pesticide immunoassay applications. This discovery established a foundational framework for constructing a tailored antibody library for pollutants.

The Caffeine Analysis in Tea Bag and Robusta Coffee Using UHPLC Methods

Caffeine, a natural psychostimulant, enhances arousal by inhibiting the effects of adenosine on the dopamine pathway. This study aimed to analyze and compare caffeine concentrations in seven robusta coffee samples (coded RC) and five black tea bags (coded BT) using both qualitative and quantitative methods. Qualitative tests employed Dragendorff reagents for coffee and Parry reagents for tea, confirming caffeine presence through colorimetric changes. Quantitative analysis utilized reverse-phase UHPLC, with a mobile phase of aquabidestilata and methanol (60:40), a C18 stationary phase at 40°C, and detection at 272 nm. Validation parameters demonstrated strong performance, with an RSD of 0.573%, a linear correlation coefficient of 0.998 for concentrations between 100–250 ppm, a LoD of 1.02 ppm, a LoQ of 3.10 ppm, and 99.88% accuracy. Results showed robusta coffee sample RC3 contained the highest caffeine concentration at 26.00 mg/serving, while black tea sample BTB3 exhibited 2.44 mg/serving. Despite higher caffeine levels in robusta coffee compared to black tea, both remained below the SNI threshold of 50 mg/serving, confirming their safety for consumption.

Quantitative analysis of acetamiprid and thiacloprid in green tea using enhanced SERS and neural networks

Neonicotinoids (NEOs) are widely used in agricultural cultivation, and the presence of residual NEOs poses a serious threat to consumer health. Therefore, trace detection of NEOs is particularly important. In this study, a response surface experimental design was employed to develop AgNP with high enhancement factor and surface height anisotropy, effectively enhancing the Raman signals of acetamiprid (ACE) and thiacloprid (THI) through densely populated hotspots on the surface. Gaussian simulation calculations were used to assign peaks in the ACE and THI spectra. Subsequently, convolutional neural network, backpropagation neural network, and AlexNet neural network were employed to identify the ACE, THI, and mixed component spectra, successfully distinguishing the spectra of the three compounds and achieving qualitative analysis of unknown spectra. Furthermore, genetic algorithm-partial least squares was used to model the spectral data, achieving a correlation coefficient of 0.97. The method was applied for the detection of spiked tea samples, achieving a precision RSD of 4.84 %. Therefore, this sensor combined with intelligent algorithms can be used for spectral identification and trace detection of mixed pesticide samples with structurally similar compounds.

SYNERGISTIC EFFECT OF HERBAL TEA SAMPLES WITH CIPROFLOXACIN AGAINST MRSA AND THEIR ANTIOXIDANT ACTIVITIES

OBJECTIVE: Sambucus nigra L. (elderberry), Salvia sclarea L. (clary sage), Rosmarinus officinalis L. (rosemary), and Coriandrum sativum L. (coriander) are all consumed as flavoring agents for food and are well-known in traditional medicine for the treating various diseases worldwide. These herbs are also commonly used for microbial infections, especially to relieve cough, fever, and cold symptoms. This study aims to screen and compare the content of total phenols and antioxidant activity potential of three different extracts from each commercial sample of S. nigra, S. sclarea, R. officinalis and C. sativum from Türkiye. We also investigated the (Minimum Inhibitory Concentration (MIC) values against Staphylococcus aureus ATCC 29213 (methicillin-susceptible, MSSA) and Staphylococcus aureus ATCC 43300 (methicillin-resistant, MRSA) and the synergistic activity with an antibiotic, ciprofloxacin, by checkerboard assay. MATERIAL AND METHODS: The fruits of S. nigra and C. sativum, the aerial parts of S. sclarea, and the leaves of R. officinalis were purchased from a trading company that marketed them as herbal tea in Türkiye. This study investigated the total phenolic content and antioxidant potential of extracts from commercial samples. We also determined the synergistic effect of herbal tea samples with ciprofloxacin against methicillin-resistant Staphylococcus aureus (MRSA). RESULTS: R. officinalis (rosemary) and Salvia sclarea (clary sage) extracts showed high phenolic content and antioxidant activity, whereas it was determined that C.sativum (coriander) and S. nigra (elderberry) extracts exhibited lower antioxidant activity and low phenolic compounds. Moreover, ciprofloxacin in combination with the ethanolic extract of S. sclarea showed additive antibacterial activity against S. aureus ATCC 43300. CONCLUSIONS: We conclude that herbal tea prepared from commercial R. officinalis (rosemary) and S.sclarea (clary sage) samples can support the antioxidant activity with high phenolic content and that ciprofloxacin combined with the ethanolic extract of clary sage showed additive antibacterial activity against methicillin-resistant S. aureus ATCC 43300. Further studies are needed to understand the mechanism of additive action in detail.

Flower-Shaped PCR Scaffold-Based Lateral Flow Bioassay for Bacillus cereus Endospores Detection

Bacillus cereus, a foodborne pathogen, produces resilient endospores that are challenging to detect with conventional methods. This study presents a novel Flower-Shaped PCR Scaffold-based Lateral Flow Biosensor (FSPCRS-LFB), which employs an aptamer-integrated PCR scaffold as capture probes, replacing the traditional streptavidin-biotin (SA-Bio) approach. The FSPCRS-LFB demonstrates high sensitivity and cost-efficiency in detecting B. cereus endospores, with a limit of detection (LOD) of 4.57 endospores/mL a visual LOD of 102 endospores/mL, and a LOD of 6.78 CFU/mL for endospore-cell mixtures. In chicken and tea samples, the platform achieved LODs of 74.5 and 52.8 endospores/mL, respectively, with recovery rates of 82.19% to 97.88%. Compared to existing methods, the FSPCRS-LFB offers a 3.7-fold increase in sensitivity while reducing costs by 26% over the SA-Bio strategy and 87.5% over rolling circle amplification (RCA). This biosensor provides a rapid, sensitive and cost-effective solution for point-of-care testing (POCT) of B. cereus endospores, expanding detection capabilities and offering novel approaches for pathogen detection.

Optimization of White Tea Flavanol Extraction Process by the Ultrasonic‐Assisted Deep Eutectic Solvent Method and Determination of the Antioxidant and Antibacterial Activity

ABSTRACTFlavanols have a variety of health benefits and biological activities and become the hotspot of the food development and research. In this research, flavanols were extracted from white tea by ultrasonic‐assisted deep eutectic solvent (DES) method. High‐performance liquid chromatography was used to determine the content of flavanols. The influence of four factors on the flavanol extraction yield was analyzed by single factor experiments, including deep eutectic solvent mole ratio (the mole of hydrogen bond acceptors: the mole of hydrogen bond donors), solid–liquid ratio (white tea sample weight/g: the volume of DES/mL), extraction time and extraction temperature. On the basis of single factor experiments, the factors which had significant effects on the flavanol extraction yield were further optimized by the response surface test. The results showed that the optimized extraction conditions were as follows: the mole ratio of DES 1: 4 (choline chloride: 1,2‐propanediol), the solid–liquid ratio 1:30, the extraction temperature 56°C, the extraction time 53 min, and the ultrasonic power 341 W. Under the above parameters, the extraction yield of white tea flavanols was 9.63 mg/g. After purification with macroporous resin, antioxidation and antibacterial experiments were carried out. The results showed that the antioxidant and antibacterial effects of white tea flavanols were remarkable. The antibacterial effects performed best on Escherichia coli, followed by Bacillus subtilis and Staphylococcus aureus. The maximum diameter of the antibacterial zone on Escherichia coli was 0.95 ± 0.11 mm. The best radical scavenging rates of OH, ABTS+ and DPPH were 97.1%, 97.5%, and 88.4%, respectively, when the flavanol concentration was 9.5 mg/mL. The conclusions of this research can provide theoretical foundation for the further study of white tea flavanols.