Study on Stabilizing Mechanism of Konjac Glucomannan in Tea Infusions

ABSTRACT:  The stabilizing mechanism of konjac glucomannan (KGM) in tea infusions was studied using a conventional transmission electron microscope (TEM), scanning electron microscope (SEM), ethanol sedimentation, and other methods. As a result, many water-soluble complexes among the KGM molecules and tea components such as thearubigins (TRs), theaflavins (TFs), total catechins (TC), and tea polyphenols (TPP) were obviously formed in tea infusions with addition of KGM. The aggregations of tea components, which caused tea cream down, were decreased because of KGM addition and the stability of suspended particles in tea-KGM infusions was enhanced. These findings suggested that the strong adsorption happened among KGM and tea components and particles through strong hydrogen bonding functions. Molecular weight of KGM in tea infusions was smaller than that in water solution. In water solution, it was 4.83 × 10⁵, but in black tea infusions 3.41 × 10⁵, and in oolong tea infusions 3.51 × 10⁵. The experiments also revealed that the tea-KGM infusions had stronger antielectrolyte coagulation capacity and the static electrification action exists among the molecules of tea infusions. These findings indicated that KGM could be a useful stabilizer for stability of the tea infusions.     

福鼎大白茶树鲜叶不同茶制品活性成分比较

目的 分析比较福鼎大白茶树鲜叶加工制成的3种茶类中活性成分的含量差异。方法 以福鼎大白茶树鲜叶为原料, 按不同工艺制成绿茶、白茶、红茶, 测定其活性成分(茶多酚、咖啡碱、氨基酸、儿茶素)含量。结果 绿茶中茶多酚及儿茶素总量最高, 红茶较低。绿茶中儿茶素总量约为红茶的10倍, 白茶中儿茶素总量约为红茶的8倍; 氨基酸含量: 白茶高于绿茶及红茶, 红茶中氨基酸最低; 咖啡碱在白茶和绿茶中的含量差别不大, 显著性高于红茶, 但不存在极显著性差异。结论 加工工艺对不同茶类茶多酚及儿茶素类物质含量影响较大, 而对咖啡碱含量的影响不大。     

Effects of pH and temperature on inactivation of Salmonella typhimurium DT104 in liquid whole egg by pulsed electric fields

Pulsed electric field (PEF) exposes a fluid or semi-fluid product to short pulses of high-energy electricity, which can inactivate microorganisms. The efficacy of PEF treatment for pasteurisation of liquid eggs may be a function of processing temperature. In this study, effects of PEF, temperature, pH and PEF with mild heat (PEF + heat) on the inactivation of Salmonella typhimurium DT104 cells in liquid whole egg (LWE) were investigated. Cells of S. typhimurium were inoculated into LWE pH adjusted to 6.6, 7.2 or 8.2 at 15, 25, 30 and 40 °C. The PEF field strength, pulse duration and total treatment time were 25 kV cm⁻¹, 2.1 μs and 250 μs respectively. Cells of S. typhimurium in LWE at pH 7.2 were reduced by 2.1 logs at 40 °C and 1.8 logs at 30 °C. The PEF inactivation of S. typhimurium cells at 15 or 25 °C was pH dependent. Heat treatment at 55 °C for 3.5 min or PEF treatment at 20 °C resulted in c. 1-log reduction of S. typhimurium cells. Combination of PEF + 55 °C achieved 3-log reduction of S. typhimurium cells and was comparable to the inactivation by the heat treatment at 60 °C for 3.5 min. With further development, PEF + heat treatment may have an advantage over high-temperature treatment for pasteurisation of liquid eggs.     

Impact of heating on chemical compositions of green tea liquor

Heating pasteurization changed flavour of green tea liquor and it was a technical barrier in ready-to-drink tea production. The effect of heating on chemical compositions of green tea liquor was investigated by high performance liquid chromatography and gas chromatography–mass spectrometry. With increase of heating temperature from 85 °C to 120 °C, the green tea liquor became darker and less green, but deeper yellow in colour. During the heating, epigallocatechin gallate, epigallocatechin, epicatechin and epicatechin gallate partially epimerized, and concentration of total catechins decreased. Twenty volatiles were identified and concentrations of pentanol, cis-3-hexenol, linalool oxide I, linalool oxide II and β-ionone were decreased while phenylacetaldehyde, linalool, linalool oxide III, α-terpineol and indole increased. The decline of volatiles with pleasant odours and increase of some volatiles with unpleasant odours, such as indole (animal-like) and α-terpineol (faint ammoniacal), was considered to be responsible for the change in flavour of green tea liquor. Treatment at 85 °C caused fewer changes in liquor colour and concentrations of catechins and volatiles and it is recommended that extraction and pasteurization of canned ready-to-drink green tea should be carried out at 85 °C or less.     

Effect of PEF on microbial inactivation and physical-chemical properties of green tea extracts

The effects of pulsed electric fields (PEF) on (1) the inactivation of Escherichia coli and Staphylococus aureus in green tea beverage, and (2) the color, green tea polyphenols (GTP) content, and total free amino acids in green tea extracts were investigated. Green tea extract samples inoculated with E. coli and S. aureus were treated using a bench-scale PEF system at electric field strengths of 18.1, 27.4, and 38.4 kV/cm and total treatment times of 40, 80, 120, 160 and 200 μs. The inactivation of E. coli and S. aureus by PEF treatment at 38.4 kV/cm for 160 and 200 μs reached 5.6 and 4.9 log reductions, respectively. PEF processing caused no considerable changes in color, GTP and total free amino acids. The storage tests at 4 °C showed that synergistic effect of low temperature storage and the antimicrobial functionality of GTP resulted in a considerable reduction in the microoganisms of the PEF-treated tea beverage, extending its shelf-life to over 6 months at 4 °C.     

Inactivation of Enterobacter sakazakii by pulsed electric field in buffered peptone water and infant formula milk

The effect of high-intensity pulsed electric field (PEF) treatment on the survival of Enterobacter sakazakii suspended in buffered peptone water (BPW) and powdered infant formula milk (IFM) was evaluated. Reference medium and IFM samples were treated with PEF. Electric field intensity and treatment time were varied from 10 to 40 kV cm⁻¹ and from 60 to 3895 μs, respectively. Samples of buffered peptone water (3 g L⁻¹) and IFM were inoculated with E. sakazakii (CECT 858) (10⁹ cfu mL⁻¹) and then treated with PEF. The inactivation data were adjusted to the Weibull frequency distribution function and Bigelow model, and constants were calculated for both substrates. A maximum 2.7 log (cfu mL⁻¹) reduction was achieved in BPW after exposure of E. sakazakii to PEF for 360 μs (2.5 μs pulse width) at 40 kV cm⁻¹. In IFM, exposure of E. sakazakii to PEF, with the same conditions, led to a 1.2 log (cfu mL⁻¹) reduction. The greater the field strength and treatment time, the greater the inactivation achieved in both substrates. Even though further research will be necessary, according to the results, there are good prospects for the use of PEF in hospitals to achieve safe reconstituted infant formula before storage at refrigerated temperatures.     

模拟体外消化评定超微绿茶粉的冲泡饮用效果

测定了超微绿茶粉模拟体外消化前后多种物质的释放情况。结果表明,超微绿茶粉在体外消化过程中,游离氨基酸、总酚、总黄酮及大部分儿茶素组分释放量有所减少;咖啡碱释放量保持不变;可溶性蛋白、没食子酸、儿茶素没食子酸酯、没食子儿茶素、没食子儿茶素没食子酸酯、异槲皮素的释放量有所增加,不可萃取多酚有所释放。说明冲泡饮用超微绿茶粉有利于提高人体对茶叶的综合利用率。     

市售茶饮料中主要功效成分分析

目的研究市售茶饮料中主要品质成分含量情况,并分析其差异原因。方法采用酒石酸铁比色法测定茶多酚(teapolyphenols,TP);采用水合茚三酮比色法测定游离氨基酸总量;采用高效液相色谱法(high performance liquid chromatography, HPLC)法检测6种儿茶素以及咖啡碱(caffeine, CAF)含量。结果目前市售茶饮料以调味茶饮料居多,不同种类、不同品牌茶饮料中的茶多酚、儿茶素、CAF以及游离氨基酸含量具有明显差异。结论绿茶饮料各种主要品质成分含量较高,其次为乌龙茶饮料,红茶饮料较低。CAF含量全部样品符合国家标, TP含量仅有一款红茶饮料低于国家标准,其余均符合国家标。     

Effect of polyphenol and pH on cocoa Maillard-related flavour precursors in a lipidic model system

Polyphenol and pH influence the flavour quality of cocoa beans during roasting. Amino acids and reducing sugars are flavour precursors in cocoa beans, which develop into cocoa-specific aroma through Maillard reactions during roasting. A central composite design was applied to determine the combined effect of polyphenol and pH on the flavour precursors during cocoa roasting at 120 °C for 45 min using a lipidic model system. Polyphenol was added at 40, 80 and 120 g kg⁻¹ and pH was adjusted to 4.5, 6 and 7.5. The response surface methodology revealed that a lower concentration of amino acids and reducing sugars was obtained at higher polyphenol concentration (120 g kg⁻¹) and lower pH value (4.5). Based on the constraints set, the best polyphenol concentration of 43–58 g kg⁻¹ and pH of 7.0–7.5 was found to be optimum for the formation of flavour precursors in this lipidic model study.     

New Kinetic Approach to the Evolution of Polygalacturonase (EC 3.2.1.15) Activity in a Commercial Enzyme Preparation Under Pulsed Electric Fields

ABSTRACT:  The effect of pulsed electric fields (PEF) on polygalacturonase (PG) activity in an aqueous solution of a commercial enzyme preparation was studied. Monopolar square wave pulses of 4 μs were delivered to the solution, which circulated through tubular chambers with 2 stainless steel electrodes in continuous operation. The electric field intensities ( E ) and treatment time ( t ) ranged within 15 to 38 kV cm⁻¹ and 300 to 1100 μs, respectively. Although important reduction of the PG activity could be achieved (up to 76.5% at E = 38 kV cm⁻¹ and t = 1100 μs), the experimental data showed certain enhancement of PG activity under soft conditions (up to 110.9% at E = 15 kV cm⁻¹ and t = 300 μs). A kinetic mechanism involving 2 consecutive irreversible first-order steps was developed to describe and explain the experimental data. The tested model exhibited high accuracy in respect of the experimental data and the error of the model was lower than 4.4%. The kinetic rate constant of the first ( k ₁) and second step ( k ₂), ratio between the activities of intermediate and native forms of the enzyme (Λ), and other quantities related to the model, were obtained within a Bayesian framework. k ₁ resulted independent of the E applied and considerably greater in magnitude order ( k ₁ mean = 6 μs⁻¹) with respect to k ₂, which was dependent on the applied E (mean values ranged from 489E-6 μs⁻¹ at E = 38 kV cm⁻¹ to 1215E-6 μs⁻¹ at 38 kV cm⁻¹). The dependency of k ₂ toward E was described using an exponential relationship.     

Effects of phosphorus supply on the quality of green tea

Self-rooted, 10-month-old, uniform tea [Camellia sinensis (L.) O. Kuntze cv. Huangguanyin] plants were supplied with 0, 40, 80, 160, 400 or 1000 μM phosphorus (P) for 17 weeks to determine how P-deficiency affects the quality of green tea. Leaf P concentration increased with increasing P supply. Whole plant dry weight (DW) increased as P supply increased from 0 to 160 μM, then remained little changed with further increasing P supply. The P-deficient green tea displayed decreased concentrations of water extract, total polyphenols, flavonoids, total free amino acids, theanine (Thea) and asparagic acid (Asp) + glutamic acid (Glu), increased concentrations of water soluble sugars, valine (Val), γ-aminobutyric acid (GABA), proline (Pro) and cysteine (Cys), and ratio of total polyphenols to total free amino acids, but unchanged concentrations of total catechins and epigallocatechin gallate (EGCG). In conclusion, the sensory and biochemical qualities of green tea were lowered by P-deficiency.     

Colour degradation and rheology of green chilli puree during thermal processing

The kinetics of degradation of both green- and total-colour of green chilli puree was studied at selected temperatures (50–90 °C). A fractional conversion concept was applied to determine the kinetic parameters. The degradation of green- and total-colour followed first order reaction kinetics. In the case of green colour the data was based on changes in Hunter – a value while L  ×  a  ×  b was found to adequately represent total colour change. Dependence of the rate constant during heat treatment obeyed the Arrhenius relationship. The activation energy values for green- and total-colour degradation were 23.04 and 25.02 kJ mol^–1, respectively. These results indicated that total colour should be used as the quality indicator during thermal processing of green chilli puree. The pungency of green chilli puree decreased during thermal processing as the capsaicin content was reduced from 559 to 441 μg g^–1 while the Scoville heat unit decreased from 8500 to 7480. The puree behaved as a shear-thinning fluid and the flow activation energy at 100 r.p.m. equalled 19.22 kJ mol^–1.     

Comparison of bioactive components in GABA tea and green tea produced in Taiwan

The aim of this study is to investigate the bioactive components of GABA (γ-aminobutyric acid) tea as compared with green tea produced in Taiwan. Using in total 56 tea samples (28 green tea and 28 GABA tea), moisture content, Hunter L, a and b values, phenolic compounds, amino acids including GABA, fatty acids and ascorbic acid were determined. The results showed that moisture, total free amino acids, crude fat, Hunter L value, total nitrogen, free fatty acids and reducing sugar did not differ significantly between GABA tea and green tea. However, GABA tea had higher Hunter a and b values, while green tea had higher total catechin and ascorbic acid contents (p < 0.05). Of major catechins, epicatechin and epigallocatechin gallate were found to be lower in GABA tea than in green tea. For free amino acids, GABA, alanine, ammonia, lysine, leucine and isoleucine were found to be significantly higher in GABA tea, while the glutamic acid, aspartic acid, and phenylalanine were higher in green tea (p < 0.05). Theanine, tryptophan, valine, threonine and methionine were not found to be different between the two kinds of tea.     

Antioxidant and antimicrobial activities of tea infusions

Tea polyphenols, especially the catechins, are potent antimicrobial and antioxidant agents, with positive effects on human health. White tea is one of the less studied teas but the flavour is more accepted than that of green tea in Europe. The concentrations of various catechins in 13 different kinds of infusion were determined by capillary electrophoresis. The total polyphenol content (Folin–Ciocalteu method), the trolox equivalent antioxidant capacity (TEAC value determined with the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation) and the inhibitory effects of infusions on the growth of some microorganisms were determined. Five different infusions (black, white, green and red teas and rooibos infusion) were added to a model food system, comprising a sunflower oil-in-water emulsion containing 0% or 0.2% bovine serum albumin (BSA), and the oxidative stability was studied during storage at 37 °C. Oxidation of the oil was monitored by determination of the peroxide value.     

Assessment of the microbiological conditions of red-meat carcasses from bacterial counts recovered by sampling via excision or swabbing with cotton wool

Samples from 240 carcasses were collected from four animal species (porcine, ovine, bovine and equine). Two samples were taken from each carcass, one using the excision method (EX) and the other the wet–dry swabbing method (SW). Eight areas from each carcass were sampled. Most of the samples obtained by SW revealed total aerobic viable counts (TVC) levels of between 3.1 and 4.0 log CFU cm⁻², while most of the values corresponding to excision were located between 4.1 and 5.0 log CFU cm⁻². Moreover, Enterobacteriaceae (EC) counts were only detected above 3.0 log CFU cm⁻² in 0.85% of the carcasses when the samples were collected by swabbing, while the excision method revealed that 13.75% of the carcasses presented EC greater than 3.0 log CFU cm⁻². TVC and EC by EX revealed statistically significant differences compared to SW, while no significant linear relationship was found between carcass surface bacterial counts obtained by SW and EX.     

Removal of imidacloprid and acetamiprid from tea infusions by microfiltration membrane

Removal of imidacloprid and acetamiprid in tea infusions by microfiltration membrane using dead‐end model was investigated in the present study. The results showed that microfiltration significantly promoted the removal of both pesticides (P < 0.05) in tea infusions. Furthermore, the extent of removal was strongly influenced by the pore size of membrane, operational pressure and the concentrations of tea infusions. The initial concentration of imidacloprid and acetamiprid showed no significant effect on their removal rates. The maximum removal rates were 79.7% for imidacloprid and 81.9% acetamiprid. The changes in major chemical components of tea infusions after microfiltration were evaluated. The results indicated that microfiltration caused no considerable changes in total polyphenols and total free amino acids, and small but statistically significant losses (6.3–18.0%) of eight catechins and three methylxanthines when filtration volume reached to 200 mL. The present study validated the application of microfiltration as a potentially feasible and promising method for the removal of imidacloprid and acetamiprid residues from tea infusions.     

微波杀青工艺对秋季绿茶的保绿降苦作用

目的：探究微波杀青工艺对秋季绿茶的保绿降苦作用;方法：以茶树品种碧香早秋季一芽二叶茶鲜叶为原料,在传统绿茶杀青、揉捻、干燥加工工艺的基础上,将微波杀青工艺替代传统滚筒杀青工艺,按不同微波强度、微波时间设置了14组微波杀青处理,从感官品质、滋味品质、干茶与汤色色泽三个方面探究微波杀青工艺对秋季绿茶的保绿降苦作用;结果：与传统滚筒杀青工艺相比,采用微波强度500w、杀青时间为3min的微波杀青工艺,所制绿茶色绿味醇且综合感官品质最佳,其水浸出物、茶多酚、氨基酸、咖啡碱、总儿茶素、简单儿茶素的含量显著升高（P<0.05）,苦味评价指标酚/氨比、酯型儿茶素含量与总儿茶素含量的比值则显著降低（P<0.05）,且干茶与茶汤色泽在绿、明度上均有不同程度的改善;结论：利用微波杀青工艺加工秋季绿茶具有较好的保绿降苦效果,可应用于提高秋季绿茶品质的生产实践。     

Enhancement of Fermentation Process in Pu-Erh Tea by Tea-Leaf Extract

ABSTRACT:  Pu-erh tea is known as a fermented tea and longer storage enhances its flavor and taste. Recently,  Aspergillu s,  Blastobotrys , and  Streptomyces  are found to play important roles in nutritional enhancement of Pu-erh tea by fermentation. Since water and temperature affect the microbial growth, we therefore explored the factors that might enhance the Pu-erh tea fermentation. The results showed that the addition of fresh tea-leaf extract (TLE) enhanced the withered tea fermentation (at 37 °C, 80 to 85% RH) as compared with the water only. Contents of statin, GABA, gallic acid, DPPH scavenging and polyphenol oxidase (PPO) activities were increased, whereas polyphenols and caffeine were decreased over 6 mo. TLE dose-dependently enhanced some of the qualities (that is, statin, PPO) of Pu-erh tea significantly as compared with the water only. The effect was related to the increase population of  A. niger  and  A. carbonarius  at 6 mo (from 7.6 ± 1.2 × 10¹ and 3.2 ± 1.3 × 10¹ to 3.1 ± 1.2 × 10⁶ and 2.4 ± 1.1 × 10⁵ colony forming units [CFU]/g, respectively). After drying process (90 °C, 30 min), the total microbial count from these samples returned to background level (3 ± 0.5 × 10² CFU/g). None of ochratoxin and fumonisin, toxins from  Aspergillus , was detected in the final products. The flavor and taste were also enhanced by treatment with TLE. The inoculation with  S. cinereus  Y11 with 2% TLE further enhanced these functional contents (about 2-fold increase of statin level) in the experimental Pu-erh tea. Therefore, this result may add a new process for Pu-erh tea manufacture.     

信阳毛尖茶的化学成分

信阳毛尖茶是中国传统名茶之一,品质优异。对信阳毛尖茶的主要化学成分进行了综述和分析。结果表明,信阳毛尖茶的茶多酚含量、儿茶素含量及非酯型儿茶素比例较高,氨基酸含量、咖啡碱含量、可溶性糖含量也比较高,形成了信阳毛尖茶鲜浓、爽口、耐泡的滋味特征;叶绿素含量高于多数嫩度相近的名绿茶,使其具有干茶色泽翠绿的品质特征;信阳毛尖茶还含有丰富的无机元素。     

Comparative Flavonoids Contents of Selected Herbs and Associations of Their Radical Scavenging Activity with Antiproliferative Actions in V79-4 Cells

ABSTRACT:  To elucidate the health benefit of herbal teas on the cytotoxicity induced by H₂O₂ in V79-4 cells, herbal extracts and its flavonoids were tested using lactate dehydrogenase release and determining intracellular reactive oxygen species generation and antioxidant activity with superoxide radical scavenging assay. Significant decrease in cell viability was observed on V79-4 cells treated with H₂O₂ (1 mM), while herbal extracts and its flavonoids including catechin and epigallocatechin gallate prevented the LDH release from H₂O₂ cytotoxicity. Total catechin contents of green tea (65.6 mg/g of dry matter) were significantly higher than other herbal teas (35.8 to 1.2 mg/g of DM). The relative concentration of the 4 major tea catechins ranked EGCG > EGC > EC > C. Green tea exhibited the lowest IC₅₀ values (2 g fresh herb/100 mL) of superoxide radical scavenging activity among the tested herbal tea, which indicates powerful antioxidant activity in O₂^·− radicals scavenging, followed by black tea, dandelion, hawthorn, rose hip, chamomile.