茶多酚在食品中的应用

茶多酚广泛应用于食品贮藏保鲜,是一种天然高效的食品添加剂。本文中,笔者介绍了茶多酚的主要成分、生物活性及其在食品工业(包括水产品、肉类及肉制品、果蔬、油脂、功能性食品等)中的应用,并展望了茶多酚在食品贮藏保鲜领域中的应用前景。     

茶多酚提取优化工艺研究

本文研究了可食用茶多酚的提取优化工艺。萃取剂为乙醇,料液比1：15,浸提过程伴随300W超声波震荡,就乙醇的浓度、提取温度、提取时间和提取次数等因素利用正交设计筛选了茶多酚的最佳提取工艺条件,并对浸提液最佳离子沉淀方法作了比较。结果表明,茶多酚提取的最佳工艺条件为：65％的乙醇溶液作浸提剂,当浸提温度为50℃,浸提时间30min,两次超声波辐射浸提后茶多酚从粗茶叶中的提取率为20．1％。沉淀剂AlCl3和ZnSO4质量比为1：2对茶多酚的沉淀效果最佳,pH=6．0。     

茶叶中多酚类物质的研究进展

本文对茶叶中的多酚类物质研究进展进行了综述,介绍了茶叶中多酚类物质的种类、含量及其结构;茶多酚的生物学活性,茶多酚的提取方法及其应用现状。为茶多酚的进一步开发利用提供参考。     

茶叶中咖啡因和茶多酚提取技术研究

本文研究茶叶品种和质量、提取剂种类和萃取溶剂量对咖啡因和茶多酚提取得率、提取率和纯度的影响,结果表明:茶叶质量高,咖啡因和茶多酚的含量、得率和纯度就高。95％乙醇提取咖啡因和茶多酚的得率、提取率和纯度最高。1％氧化钙水溶液单纯提取咖啡因的得率、提取率和纯度较高。增加萃取次数和萃取溶剂量可提高咖啡因和茶多酚的得率,对产品纯度没有影响。     

肠道微生物与茶及茶多酚的相互作用在调节肥胖及并发症中的作用

肠道微生物、茶及茶多酚与肥胖及并发症密切相关,它们之间的相互作用是食品、医疗、生物等领域的研究热点。本文就肠道微生物、茶及茶多酚以及它们之间的相互作用对肥胖及并发症的影响进行综述,阐明茶及茶多酚通过肠道微生物来调节肥胖及并发症的机理机制,以期为茶叶功能成分研究与产品开发提供依据。     

茶叶不同提取成分降血糖作用的研究与比较

目的:探讨茶多糖、茶多酚、茶色素对血糖的降低作用.方法:用链脲佐菌素(STZ)建立糖尿病小鼠模型.提取茶多糖,茶多酚,茶色素,作用于糖尿病小鼠.通过葡萄糖氧化酶法(GOD-POD)测定血糖含量,研究并比较各成分的降血糖作用.结果:茶多酚,茶色素具有明显的降血糖作用,茶多糖的降血糖作用不明显.结论:茶多糖,茶多酚,茶色素均具有降血糖的作用.     

茶多酚的提取及其对抗生素所致肠道菌群失衡的调整和预防作用

为评价茶多酚对抗生素所致小鼠肠道菌群失衡的调整和预防作用,采用ZnCl2沉淀,乙酸乙酯萃取法提取茶多酚,HPLC检测提取效果;将BALB/c小鼠随机分为正常对照、失调模型、预防和治疗组,定期留取粪便,以自主改进法提取粪便细菌基因组总DNA,PCR-DGGE获得肠道菌群分子指纹图谱,进行相似性、多样性及主要差异条带序列的分析。结果表明提取茶多酚中有效成分EGCG的含量为42.67%;改进的溶菌酶法可有效对粪便细菌总DNA进行提取并保证下游分析顺利开展;DGGE分析显示治疗组和预防组电泳条带与正常对照组比较差异较小(P0.05),提示茶多酚对抗生素所致肠道菌群失衡具有一定的调整和预防作用,预防效果更佳。     

脂溶性茶多酚的合成及其抗油脂自动氧化特性的研究

茶多酚是一种天然无毒的食品抗氧化剂,但其难溶于油的特性限制了其在食品领域的广泛使用,本研究通过对其进行化学修饰,制备出了一种 脂溶性的茶多酚（LTP）。重点研究了皮应物配比、催化剂用量、反应温度和气氛对反应的影响以及粗产品的纯化方法,并初步探讨了其抗油脂自动氧化的特性,结果表明,最佳的反应条件为：茶多酚、癸多酚、癸酰氯、催化剂质量比为1：2．3：0．05,于氮气保护、100℃下反应4h后水洗处理。所得产品具有与合成抗氧化剂BHT相当的抗氧化活性。     

响应面优化饮品中茶多酚磷脂复合物抑菌配方的研究

以茶多酚磷脂复合物为研究对象,以茶多酚磷脂复合物对大肠杆菌的抑菌圈直径作为抑菌效果指标,对茶多酚磷脂复合物的抑菌条件进行了研究。考察茶多酚磷脂复合物浓度、壳聚糖浓度、柠檬酸浓度对大肠杆菌抑菌圈值的影响。在单因素试验的基础上,采用3因素3水平的响应面分析法对茶多酚磷脂复合物对大肠杆菌的抑制条件进行了优化,依据回归分析确定最优提取条件。结果表明,最佳抑菌条件为:茶多酚磷脂复合物的浓度为3.22 g/L,壳聚糖浓度为31.06 g/L,柠檬酸浓度为2.45 g/L。在此抑菌条件下,茶多酚磷脂复合物对大肠杆菌的抑制圈值达到最大,为18.1 mm。     

肾茶多酚提取工艺及其抗氧化活性研究

采用回流提取法,进行单因素试验和L9(34)正交试验,确定肾茶多酚最佳提取工艺;并通过测定1,1-二联苯基-2-苦肼自由基(DPPH·)和羟自由基(·OH)清除率评价其抗氧化活性。得到的肾茶多酚的优化提取工艺为液料比10∶1(m L/g),50%乙醇回流3次,每次提取2 h,肾茶多酚提取率为3.60%,优选的提取工艺稳定可靠,重现性好。体外抗氧化活性实验结果显示:肾茶多酚的抗氧化能力随质量浓度的增大而增强,在1~10μg/m L浓度范围内和100~1250μg/m L浓度范围内,其清除DPPH自由基和羟基自由基的能力略强于抗坏血酸,两者的对DPPH自由基半数抑制浓度分别为5.78和6.31μg/m L;对羟基自由基的半数抑制浓度为851.1和940.1μg/m L。     

茶多酚的抗氧化和抑菌活性及其增效剂

论述了茶多酚的抗氧化和抑菌活性机理,其中起重要作用的是茶多酚分子内的多个酚羟基。在抗氧化过程中,其酚羟基具有供氢体的活性,阻断自由基的链式反应。在抑菌过程中,其酚羟基可与蛋白质分子中的氨基或羧基结合,其疏水性的苯环结构也可与蛋白质发生疏水结合,茶多酚与蛋白质之间的这种多点结合作用阻止了细菌的侵染,使其具有抑菌性。作为增效剂,有机酸、β-胡萝卜紊等能够增强茶多酚的抗氧化性能;壳聚糖、食盐等能够增强茶多酚的抑菌活性．维生素类既能够增强茶多酚的抗氧化性能又能增强其抑菌作用。     

Cancer chemoprevention by tea polyphenols

Tea is one of the most widely consumed beverages, second only to water. Many experimental researches in laboratory animals demonstrated that tea components had an inhibitory effect on carcinogenesis at a number of organ sites. The inhibitory effects of tea against carcinogenesis have been attributed to the biologic activities of the polyphenol fraction in tea. This review summarizes experimental data on chemopreventive effects of tea polyphenols in various tumor bioassay systems. Many laboratory studies have demonstrated the inhibitory effects of green tea polyphenols, especially (-)-epigallocatechin-3-gallate (EGCG), on carcinogenesis in animals models. The majority of these studies have been conducted in mouse skin tumor models, where tea polyphenols were used either as oral feeding in drinking water or in direct local application. Most studies used 12-O-tetradecanoylphorbol-13-acetate (TPA) or ultraviolet (UV) radiation as the tumor promoter and found anticarcinogenic effects caused by green tea polyphenols. Black tea was also found to be effective, although the activity was weaker than that of green tea in some experiments. Other studies showed that black tea polyphenols-theaflavins exhibited stronger anticarcinogenic activity than did EGCG. Caffeine in tea was also important for tea to prevent tumorigenesis. The molecular mechanisms of the cancer chemopreventive effects of tea polyphenols are not completely understood. They are most likely related to the mechanisms of biochemical actions of tea polyphenols, which include antioxidative activities, modulation of xenobiotic metabolite enzymes and inhibition of tumor promotion. In addition, we have also proposed that tea polyphenols function as cancer chemopreventive agents through modulation of mitotic signal transduction. However, the molecular mechanisms involved in this modulation need further investigation.     

Analysis of tea polyphenols

Tea is the most highly consumed beverage in the world, other than water. However, unlike water, tea contains substantial amounts of polyphenols that have unique biological activities and may be responsible for many of the health benefits of tea. As a result, it is essential to be able to measure the various tea-associated polyphenols. Total polyphenol content is currently measured by using methodology based on reducing activity. Several HPLC systems with detectors that, collectively, have wide ranges in sensitivity have been developed for analysis of individual flavonoids in tea and biological samples, and for theaflavins in tea. Catechins also have been measured in plasma by solid phase extraction, addition of a chromophore, and colorimetric quantification. Except for theaflavins in tea, routine and robust methods for the measurement of polyphenol condensation products (dimers and thearubigens) in tea and biological samples have not been developed. Although in vitro and animal studies suggest substantial metabolism of flavonoids in the gastrointestinal tract, only a single HPLC procedure has been assembled for monitoring the metabolic products of quercetin in urine of human subjects.     

Antiviral activity of green tea and black tea polyphenols in prophylaxis and treatment of COVID-19: A review

BackgroundThe rapid spread of novel coronavirus called SARS-CoV-2 or nCoV has caused countries all over the world to impose lockdowns and undertake stringent preventive measures. This new positive-sense single-stranded RNA strain of coronavirus spreads through droplets of saliva and nasal discharge.PurposeUS FDA has authorized the emergency use of Remdesivir looking at the increasing number of cases of COVID-19, however there is still no drug approved to treat COVID-19. An alternative way of treatment could be the use of naturally derived molecules with known antiviral properties.MethodWe reviewed the antiviral activities of two polyphenols derived from tea, epigallocatechin-3-gallate (EGCG) from green tea and theaflavins from black tea. Both green tea and black tea polyphenols have been reported to exhibit antiviral activities against various viruses, especially positive-sense single-stranded RNA viruses.ResultsRecent studies have revealed the possible binding sites present on SARS-CoV-2 and studied their interactions with tea polyphenols. EGCG and theaflavins, especially theaflavin-3,3′-digallate (TF3) have shown a significant interaction with the receptors under consideration in this review. Some docking studies further emphasize on the activity of these polyphenols against COVID-19.ConclusionThis review summarizes the available reports and evidences which support the use of tea polyphenols as potential candidates in prophylaxis and treatment of COVID-19.     

Mechanisms of inhibition of carcinogenesis by tea

Tea (Camellia sinensis) preparations have been shown to inhibit tumorigenesis at the initiation, promotion, and progression stages in different animal models. The anti-proliferative effects of tea polyphenols may be a key mechanism, especially in the NNK-induced lung tumorigenesis model with mice. Studies with cell lines have demonstrated that tea polyphenols inhibit cell proliferation and induce apoptosis. The effective concentrations used in these studies (20-100 microM) are usually higher than those observed in blood and tissues of humans and animals, which are in the low micromolar range. Glucuronide and sulfate conjugated and methylated catechins as well as ring fission products (due to intestinal microflora) have been observed in human plasma and urine. Purified green and black tea polyphenols inhibited the H-ras induced milogen-activated protein kinases, AP-1 activities, and the growth of 30.7b Ras 12 and BES21 cells. Among the catechins, both the galloyl structure on the B ring and the gallate moiety are important for the inhibition. Both (-)-epigallocatechin-3-gallate and theaflavin-3,3'-digallate inhibited the phosphorylation of c-jun and p44/42 (ERK 1/2). More mechanistic and human studies in these areas will help us to understand the possible inhibitory action of tea against carcinogenesis in humans.     

Antimutagenic and anticarcinogenic activity of tea polyphenols

Tea is the most popular beverage, consumed by over two thirds of the world's population. Tea is processed differently in different parts of the world to give green (20%), black (78%) or oolong tea (2%). Green tea is consumed mostly in Japan and China. The antimutagenic and anticarcinogenic activities of green tea are extensively examined. The chemical components of green and black tea are polyphenols, which include EC, ECG, EGC, EGCG and TFs. This article reviews the epidemiological and experimental studies on the antimutagenicity and anticarcinogenicity of tea extracts and tea polyphenols. In Japan, an epidemiological study showed an inverse relationship between habitual green tea drinking and the standardized mortality rates for cancer. Some cohort studies on Chanoyu (Japanese tea ceremony) women teachers also showed that their mortality ratio including deaths caused by malignant neoplasms were surprisingly low. The antimutagenic activity against various mutagens of tea extracts and polyphenols including ECG and EGCG has been demonstrated in microbial systems (Salmonella typhimurium and Escherichia coli), mammalian cell systems and in vivo animal tests. The anticarcinogenic activity of tea phenols has been shown in experimental animals such as rats and mice, in transplantable tumors, carcinogen-induced tumors in digestive organs, mammary glands, hepatocarcinomas, lung cancers, skin tumors, leukemia, tumor promotion and metastasis. The mechanisms of antimutagenesis and anticarcinogenesis of tea polyphenols suggest that the inhibition of tumors may be due to both extracellular and intracellular mechanisms including the modulation of metabolism, blocking or suppression, modulation of DNA replication and repair effects, promotion, inhibition of invasion and metastasis, and induction of novel mechanisms.     

Black tea represents a major source of dietary phenolics among regular tea drinkers

The phenolic composition and antioxidant activities [TEAC, ORAC, FRAP] of consumer brews (1 tea bag in 230 ml for 1 min) of seven different brands of black tea from the British market were investigated. The main phenolic compounds identified were epigallocatechin gallate, four theaflavins, as well as epicatechin gallate, theogallin (tentative assignment), quercetin-3-rutinoside and 4-caffeoyl quinic acid. Thearubigins represented an estimated 75-82% of the total phenolics. Further, polyphenol fractions were in decreasing order theaflavins, flavan-3-ols, flavonols, gallic acids and hydroxycinnamates. On average, a cup of a consumer brew of black tea is providing polyphenols at the level of 262 mg GAE/serving, of which 65 mg were assigned to individual polyphenols. The antioxidant activity of black tea preparations is higher than that of most reported dietary agents on a daily basis. Correlations were observed between the antioxidant activities and the sum of all quantified polyphenols by HPLC analysis as well as with the total phenolics. Treatment of the black tea brew with simulated gastric juice resulted in a significant increase of the identified theaflavins implying a partial cleavage of thearubigins in the environment of the gastric lumen. Therefore, black tea can be considered to be a rich source of polyphenols and/or antioxidants.     

Green tea polyphenols enhance sodium nitroprusside-induced neurotoxicity in human neuroblastoma SH-SY5Y cells

Oxidative stress is a main mediator in nitric oxide (NO) -induced neurotoxicity and has been implicated in the pathogenesis of many neurodegenerative disorders. Green tea polyphenols are usually expected as potent chemo-preventive agents due to their ability of scavenging free radicals and chelating metal ions. However, not all the actions of green tea polyphenols are necessarily beneficial. In the present study, we demonstrated that higher-concentration green tea ployphenols significantly enhanced the neurotoxicity by treatment of sodium nitroprusside (SNP), a nitric oxide donor. SNP induced apoptosis in human neuroblastoma SH-SY5Y cells in a concentration and time-dependent manner, as estimated by cell viability assessment, FACScan analysis and DNA fragmentation assay, whereas treatment with green tea polyphenols alone had no effect on cell viability. Pre-treatment with lower-dose green tea polyphenols (50 and 100 microm) had only a slightly deleterious effect in the presence of SNP, while higher-dose green tea polyphenols (200 and 500 microm) synergistically damaged the cells severely. Further research showed that co-incubation of green tea polyphenols and SNP caused loss of mitochondrial membrane potential, depletion of intracellular GSH and accumulation of reactive oxygen species, and exacerbated NO-induced neuronal apoptosis via a Bcl-2 sensitive pathway.     

Comparative antimutagenic and anticlastogenic effects of green tea and black tea: a review

Tea is the most popular beverage next to water, consumed by over two-thirds of the world's population. It is processed in different ways in different parts of the world to give green, black or oolong tea. Experimental studies have demonstrated the significant antimutagenic and anticlastogenic effects of both green and black tea and its polyphenols in multiple mutational assays. In the present review, we have attempted to evaluate and update the comparative antimutagenic and anticlastogenic effects of green tea, black tea and their polyphenols in different test systems, based on available literature. Existing reports have suggested that the protective effects of black tea is as good as green tea, however, more studies on black tea and its polyphenols are needed before a final conclusion can be made.