Effect of the type of brewing water on the sensory and physicochemical properties of light-scented and strong-scented Tieguanyin oolong teas

Variations in the quality of brewing water profoundly impact tea flavor. This study systematically investigated the effects of four common water sources, including pure water (PW), mountain spring water (MSW), mineral water (MW) and natural water (NW) on the flavor of Tieguanyin tea infusion. Brewing with MW resulted in a flat taste and turbid aroma, mainly due to the low leaching of tea flavor components and complex interactions with mineral ions (mainly Ca2+, Mg2+). Tea infusions brewed with NW exhibited the highest relative contents of total volatile compounds, while those brewed with PW had the lowest. NW and MSW, with moderate mineralization, were conducive to improving the aroma quality of tea infusion and were more suitable for brewing both aroma types of Tieguanyin. These findings offer valuable insights into the effect of brewing water on the sensory and physicochemical properties of oolong teas.

Comparative study on the in vitro digestibility of chicken protein after different modifications

The effects of tea polyphenols (TPPs) and ultrasound treatment (UDT) on the digestibility of chicken myofibrillar protein (MPN) in anenhanced oxidation system were investigated. As observed, the original aggregates of MPN were much lower in the UDT-assisted group than in the control protein group, and the difference widened after the incorporation of TPPs. The covalent structures of the UDT-assisted oxidation groups were verified via mass spectrometry and amino acid (AAD) measurements. The peptide abundance increased after the UDT-assisted covalent reaction and most of these peptides were derived from the structural proteins of MPNs according to the results of nano-LC-ESI-MS/MS. Digestion kinetic analysis showed that the digestion level of the EGCG-treated group was better than that of the other treated groups, regardless of the UDT-assisted covalent reaction. Overall, the combination of EGCG oxidation and UDT may be an efficient way to promote the nutritional value of the final MPN products.

Sensory and chemical characteristics of Tieguanyin oolong tea after roasting

Roasting, a critical process for oolong tea, has been applied to Tieguanyin tea to improve flavor attributes. To investigate the effects of the roasting on the flavor of Tieguanyin, the global metabolomics analysis on the non-volatile and volatile components were proceeded. The weakening of bitterness and astringency, caused by roasting, may be attributed to the decreasing of flavonoids glycosides and procyanidins, whereas the enhancing of sweet aftertaste to the increasing of gallic acid. Besides, l-theanine flavan-3-ols adducts (N-ehtyl-2-pyrrolidinone substituted flavan-3-ols) increased dramatically at 130 °C compared with 105 °C, with the reduction of l-theanine and flavan-3-ols. Meanwhile, high temperature hampered the volatiles' diversity and intensity, resulting from the lowering of floral volatiles, i.e., β-ionone, jasmine, and nerolidol, yet the nitrogen-containing heterocyclic compounds increased, e.g., pyrroles and pyrazines. The results can help to comprehensively understand the influences of roasting technology on the flavor and chemistry of oolong tea.

Effects of brewing water on the sensory attributes and physicochemical properties of tea infusions

The effects of brewing water on the sensory attributes and physicochemical properties of tea infusions made from Chinese teas were investigated. The tea infusions brewed in water with higher pH and total dissolved solids (TDS), generally had a darker color and lower overall sensory acceptability. Moreover, those infusions had less catechins, particularly galloylated-catechins, and lower antioxidant capacity. The teas with less fermentation contained more galloylated-catechins and had higher antioxidant capacity, but were much more susceptible to high mineral brewing water. Green tea was proved to be the most susceptible one, whereas dark tea the most stable one. Green tea infusions prepared with higher pH/TDS water were more rapidly oxidized, resulting in a darker color due to polymerization of catechins, when exposed to the air. These findings suggested that low mineral brewing water was better for Chinese tea, both from the sensory and health benefit perspectives.

Ionic liquid@β-cyclodextrin-gelatin composite membrane for effective separation of tea polyphenols from green tea

A new kind of multi-component membrane was prepared by combining gelatin solution, porogen and an inclusion complex of ionic liquid (IL) and beta-cyclodextrin (β-CD) in a simple physical manner for selective separation of tea polyphenols (TPs) from green tea crude extracts. After screening, it was found that the resulting membrane containing the IL of dicationic N-vinylimidazole proline salt ([VIm]₂C₃[l-pro]₂) had the excellent performance for the enrichment of the target molecules. Then the newly-developed film was comprehensively characterized by scanning electron microscopy, conductivity, thermogravimetry and spectral analysis. Under pressure driving, the adsorption from an aqueous solution of a mixture of TPs and theophylline on IL@β-CD-Gel membrane showed that the adsorption capacity for TPs was 303.45 mg/g with removal percentages of 94.38%. The experimental data fit well with pseudo-second-order model and Freundlich model. By using this composite material, a new technology of membrane separation for selective adsorption of TPs was finally established.

Effects of epigallocatechin gallate, epigallocatechin and epicatechin gallate on the chemical and cell-based antioxidant activity, sensory properties, and cytotoxicity of a catechin-free model beverage

The effects of epigallocatechin gallate (EGCG), epigallocatechin (EGC) and epicatechin gallate (ECG) on the chemical and cell-based antioxidant activity, sensory properties, and cytotoxicity of a catechin-free model beverage were modeled using response surface methodology. Results showed that ECG presented the highest reducing capacity while EGCG presented the highest Cu²⁺ chelating ability. Binary interactions (EGCG/EGC and EGCG/ECG) had an additive effect on CUPRAC, DPPH and Cu²⁺ chelating ability. The mixture containing 67.4% ECG and 32.6% EGCG was the optimal combination of flavanols (OPC). In a beverage model - chrysanthemum tea - OPC enhanced the anti-proliferative activity in relation to OVCAR-3, HEK293 and HFL1 cells and decreased the intracellular generation of reactive oxygen species. OPC enhanced the bitterness and astringency of the beverage models impacting in a decrease in overall acceptance. The pasteurization process did not decrease the antioxidant activity and the flavanol concentration of the beverages.

A predictive model for astringency based on in vitro interactions between salivary proteins and (-)-Epigallocatechin gallate

Astringency is an important quality attribute of green tea infusion, and (-)-Epigallocatechin gallate (EGCG) is the main contributor to astringency. Turbidity was used to predict the intensity of astringency for EGCG. The interactions between the selected proteins and EGCG, and the impacts of temperature, pH, protein structure, and EGCG concentration were studied. Mucin was selected as the protein in study for the prediction of EGCG astringency intensity. A predictive model (R² = 0.994) was developed based on the relationship between the astringency of EGCG and the turbidity of EGCG/mucin mixtures at pH 5.0 and 37 °C. The fluorescence quenching analyses showed the interactions between EGCG and the selected proteins, which induced the reversible protein molecule conformational changes. The interactions were considered as the main reason that causes the astringency of tea infusions. The results provided a biochemical approach to explore the sensory qualities of green tea.

Improving the taste of autumn green tea with tannase

Green tea processed from autumn leaves is more bitter and astringent than that from spring leaves, mainly due to gallated catechins. The present study aimed to improve the taste of autumn green tea and green tea infusion by using tannase to treat tea leaves and tea infusion. The results showed that, after hydrolysis, the sweet aftertaste and overall acceptability improved, and the ratio of gallated catechins decreased, as did the bitterness and astringency of the autumn green tea. The pH value was significantly correlated with the concentrations of gallated catechins (r = 0.930, p < 0.01), non-gallated catechins (r = -0.893, p < 0.01), and gallic acid (r = 0.915, p < 0.01), as well as with the intensities of bitterness, astringency, and sweet aftertaste during hydrolysis. Gallic acid contributed to the sweet aftertaste of green tea infusion. These results will help to improve autumn green tea products with tannase.

The effects of dietary and herbal phytochemicals on drug transporters

Membrane transporter proteins (the ABC transporters and SLC transporters) play pivotal roles in drug absorption and disposition, and thus determine their efficacy and safety. Accumulating evidence suggests that the expression and activity of these transporters may be modulated by various phytochemicals (PCs) found in diets rich in plants and herbs. PC absorption and disposition are also subject to the function of membrane transporter and drug metabolizing enzymes. PC-drug interactions may involve multiple major drug transporters (and metabolizing enzymes) in the body, leading to alterations in the pharmacokinetics of substrate drugs, and thus their efficacy and toxicity. This review summarizes the reported in vitro and in vivo interactions between common dietary PCs and the major drug transporters. The oral absorption, distribution into pharmacological sanctuaries and excretion of substrate drugs and PCs are considered, along with their possible interactions with the ABC and SLC transporters which influence these processes.

Effect of the type of brewing water on the chemical composition, sensory quality and antioxidant capacity of Chinese teas

The physicochemical characteristics, sensory quality, and antioxidant activity of tea infusions prepared with purified water (PW), mineral water (MW), mountain spring water (MSW), and tap water (TW) from Hangzhou were investigated. The results showed that the taste quality, catechin concentration, and antioxidant capacity of green, oolong, and black tea infusions prepared using MW and TW were significantly lower than those prepared using PW. Extraction of catechins and caffeine was reduced with high-conductivity water, while high pH influenced the stability of catechins. PW and MSW were more suitable for brewing green and oolong teas, while MSW, with low pH and moderate ion concentration, was the most suitable water for brewing black tea. Lowering the pH of mineral water partially improved the taste quality and increased the concentration of catechins in the infusions. These results aid selection of the most appropriate water for brewing Chinese teas.

Metal chelation, radical scavenging and inhibition of Aβ₄₂ fibrillation by food constituents in relation to Alzheimer's disease

Various food constituents have been proposed as disease-modifying agents for Alzheimer's disease (AD), due to epidemiological evidence of their beneficial effects, and for their ability to ameliorate factors linked to AD pathogenesis, namely by: chelating iron, copper and zinc; scavenging reactive oxygen species; and suppressing the fibrillation of amyloid-beta peptide (Aβ). In this study, nine different food constituents (l-ascorbic acid, caffeic acid, caffeine, curcumin, (-)-epigallocatechin gallate (EGCG), gallic acid, propyl gallate, resveratrol, and α-tocopherol) were investigated for their effects on the above factors, using metal chelation assays, antioxidant assays, and assays of Aβ42 fibrillation. An assay method was developed using 5-Br-PAPS to examine the complexation of Zn(II) and Cu(II). EGCG, gallic acid, and curcumin were identified as a multifunctional compounds, however their poor brain uptake might limit their therapeutic effects. The antioxidants l-ascorbic acid and α-tocopherol, with better brain uptake, deserve further investigation for specifically addressing oxidative stress within the AD brain.

Improving the sweet aftertaste of green tea infusion with tannase

The present study aims to improve the sweet aftertaste and overall acceptability of green tea infusion by hydrolyzing (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG) with tannase. The results showed that the intensity of the sweet aftertaste and the score of overall acceptability of the green tea infusion significantly increased with the extension of the hydrolyzing treatment. (-)-Epigallocatechin (EGC) and (-)-epicatechin (EC) were found to be the main contributors for the sweet aftertaste, based on a trial compatibility with EGCG, ECG, EGC, and EC monomers, and a synergistic action between EGC and EC to sweet aftertaste was observed. A 2.5:1 (EGC/EC) ratio with a total concentration of 3.5 mmol/L gave the most satisfying sweet aftertaste, and the astringency significantly inhibited the development of the sweet aftertaste. These results can help us to produce a tea beverage with excellent sweet aftertaste by hydrolyzing the green tea infusion with tannase.

Effect of methylated tea catechins from Chinese oolong tea on the proliferation and differentiation of 3T3-L1 preadipocyte

As the important component of tea catechins in oolong tea, (-)-epigallocatechin 3-O-(3-O-methyl) gallate (EGCG3″Me) has exhibited various beneficial effects, however, little attention about its obesity prevention effect is available. In this study, the inhibitory effects of tea catechin monomers, including their methylated forms on the proliferation and differentiation of 3T3-L1 preadipocyte were studied. The major methylated tea catechins in oolong tea were identified as EGCG3″Me and ECG3″Me. The accumulation of triglyceride was significantly reduced in a concentration-dependent manner in groups treated with EGCG3″Me at concentrations of 20, 40 and 80μg/mL, and the accumulation of lipid was decreased to 89.42±2.66%, 64.36±3.13% and 39.37±2.79%, respectively. Both EGCG3″Me and EGCG treatments showed a significant inhibitory effect on adipogenesis, while EGCG3″Me showed a relatively higher effect than EGCG, which was contrary to the results of cytotoxic activity. For ECG and ECG3″Me, ECG3″Me also showed a relatively higher antiobesity effect and lower cytotoxic activity. The results of activity screening showed that methylated tea catechins, including EGCG3″Me and ECG3″Me inhibited the proliferation and differentiation of 3T3-L1 preadipocyte. The difference of inhibitory effects for tested compounds may be due to their structural difference (the hydroxyl group at C-3 in D ring substituted by methoxy group).