Effect of nanocomposite‐based packaging on preservation quality of green tea

An improved nanocomposite‐based packaging material (NCP) was prepared by blending polyethylene with nano‐Ag, nano‐TiO₂ and attapulgite. And its effect on preservation quality of green tea (Biluochun and Qingfeng) during one‐year ambient storage was investigated. The results showed that adding nanoparticles to the polyethylene could significantly improve the barrier property. After one‐year ambient storage, the moisture of Biluochun and Qingfeng with NCP was decreased by 10.3% and 6.1% compared with the normal packaging material. Meanwhile, the contents of amino acid, tea polyphenols, chlorophyll and ascorbic acid were increased by 22.8%, 9.4%, 30.4% and 9.5% for Biluochun and 19.2%, 9.3%, 27.3% and 21.6% for Qingfeng, respectively, compared with the normal packaging material. Moreover, the sensory quality of NCP was also superior to that with the control. Therefore, the improved NCP material probably provides an attractive alternative to maintain the preservation quality of green tea at a high level during storage.     

Textural properties of yogurts with green tea and Pu‐erh tea additive

Set‐style yogurts enriched with green tea or Pu‐erh tea infusions in three concentrations, that is, 5%, 10% and 15% (v/v), and the nonsupplemented yogurts were produced. The obtained cultured milk treatments were subjected to the analyses of acidity, viscoelastic properties, back extrusion parameters, susceptibility to syneresis and instrumental colour analysis. As revealed by the performed HPLC and spectrophotometric studies, the two types of tea differed greatly in their polyphenolic composition which was further reflected in the physicochemical properties of yogurt gels. Results indicate that yogurts varied as regards textural properties depending on the type of tea applied as well as tea concentration. Green tea incorporation, which contained significantly higher amounts of catechins, produced yogurts with increased titratable acidity, better mechanical properties and less susceptible to syneresis, while yogurt gels with Pu‐erh tea were firmer, less elastic and with visible syneresis at higher (10%, 15%) tea concentrations.     

Suppression of blood glucose level by a new fermented tea obtained by tea‐rolling processing of loquat (Eriobotrya japonica) and green tea leaves in disaccharide‐loaded Sprague‐Dawley rats

BACKGROUND: In the field of food science, much interest has been focused on the development of alternative medicinal foods with the ability to regulate excess blood glucose level (BGL) rise. The authors have successfully developed a new fermented tea product (LG tea) by co‐fermentation of loquat (Eriobotrya japonica) leaf and summer‐harvested green tea leaf. The objective of this study was to examine the acute suppression effect of LG tea on BGL rise in disaccharide‐loaded Sprague‐Dawley (SD) rats and to evaluate its possible usage as an antidiabetic functional food material. RESULTS: As a result of single oral administration of hot water extract of LG tea (50 mg kg^?1) to maltose‐loaded SD rats, BGL at 30 min was significantly decreased by 23.8% (P < 0.01) compared with the control. A corresponding reduction in serum insulin secretion was also observed. The ED₅₀ value of LG tea (50.7 mg kg^?1) was estimated to be about 16‐fold higher than that of the therapeutic drug acarbose (3.1 mg kg^?1). CONCLUSION: No significant change in BGL was observed when sucrose or glucose was administered, suggesting that the suppression effect of LG tea was achieved by maltase inhibition, not by sucrase inhibition or glucose transport inhibition at the intestinal membrane. Copyright © 2010 Society of Chemical Industry     

Enhanced cholesterol‐ and triglyceride‐ lowering effect of West African green tea

‘The Vert’ is a special type of green tea widely consumed in West Africa and locally associated with many health benefits. However, limited research has been conducted to evaluate its health benefits, such as its enhanced hypolipidemic potential. The objectives of this study were to (1) evaluate the cholesterol‐ and triglyceride‐lowering effects of West African green tea (WAGT) as affected by diet and tea intake, (2) determine the impact of WAGT consumption on the CHD risk ratio, and (3) explore possible mechanisms through which WAGT improves serum lipid profile. Forty‐five male Wistar rats were randomly assigned to one of nine treatment combinations, three diets (regular, high‐cholesterol, and trans‐fat diets) and three fluid sources (no tea, diluted tea, and concentrated tea). After 6 weeks of feeding, animal blood, liver, and feces were harvested. Total cholesterol, HDLc, LDLc, and triglycerides in serum, liver, and feces were determined. The concentrations of bile acids in feces were also measured. WAGT significantly lowered serum and liver cholesterol (30% and 15%, respectively) and increased serum HDL cholesterol (30%). It also reduced liver enlargement caused by storage of excess lipids in high‐cholesterol diet. Overall, the CHD risk ratio was cut by two‐thirds in rats fed high‐cholesterol diet and WAGT. A marked increase in fecal total lipids, cholesterol (60%), and bile acids (50%) was observed in rats that consumed WAGT compared to the control group. These beneficial effects could be attributed to the significantly high flavonoid content of WAGT. Copyright © 2007 Society of Chemical Industry     

Absorption,metabolism, and excretion of green tea flavan‐3‐ols in humans with an ileostomy

Green tea containing 634 μmol of flavan‐3‐ols was ingested by human subjects with an ileostomy. Ileal fluid, plasma, and urine collected 0–24 h after ingestion were analysed by HPLC‐MS. The ileal fluid contained 70% of the ingested flavan‐3‐ols in the form of parent compounds (33%) and 23 metabolites (37%). The main metabolites effluxed back into the lumen of the small intestine were O‐linked sulphates and methyl‐sulphates of (epi)catechin and (epi)gallocatechin. Thus, in subjects with a functioning colon substantial quantities of flavan‐3‐ols would pass from the small to the large intestine. Plasma contained 16 metabolites, principally methylated, sulphated, and glucuronidated conjugates of (epi)catechin and (epi)gallocatechin, exhibiting 101–256 nM peak plasma concentration and the time to reach peak plasma concentration ranging from 0.8 to 2.2 h. Plasma pharmacokinetic profiles were similar to those obtained with healthy subjects, indicating that flavan‐3‐ol absorption occurs in the small intestine. Ileostomists had earlier plasma time to reach peak plasma concentration values than subjects with an intact colon, indicating the absence of an ileal brake. Urine contained 18 metabolites of (epi)catechin and (epi)gallocatechin in amounts corresponding to 6.8±0.6% of total flavan‐3‐ol intake. However, excretion of (epi)catechin metabolites was equivalent to 27% of the ingested (?)‐epicatechin and (+)‐catechin.     

Polyphenolic composition and in vitro antioxidant activities of native‐ and tannase‐treated green tea extracts

The antioxidant activities of native‐ and tannase‐treated green tea extracts along with their major polyphenol components were investigated. The polyphenolic content and composition of the tea before and after tannase treatment were determined by liquid chromatography coupled with mass spectrometry (LC‐MS). Approximately 99% of the (?)‐epigallocatechin gallate (EGCG) and (?)‐epicatechin gallate (ECG) in green tea extract were converted by tannase to (?)‐epigallocatechin (EGC) and (?)‐epicatechin (EC), respectively, after 30 min. Biotransformed green tea exhibited a significantly higher DPPH˙ radical scavenging activities than native green tea (EC₅₀ value of 0.024 ± 0.001 and 0.044 ± 0.001 mg mL^?1, respectively). Kinetic parameters such as scavenging rate and stoichiometry were calculated. The rate of DPPH˙ radical scavenging activities for tannase‐treated green tea extract was shown to be higher than native green tea extract.     

Presence of two forms of methylated (–)‐epigallocatechin‐3‐gallate in green tea

Crude catechins extract from Chinese green tea were fractionated using Sephadex LH‐20 column chromatography. The fraction containing (–)‐epigallocatechin‐3‐gallate (EGCG) was then subjected to a semipreparative high‐performance liquid chromatography (HPLC). Using a mobile phase of water : dimethyl formamide : methanol : acetic acid (157 : 49 : 2 : 1 v/v/v/v( the mixture of two methylated catechins was separated and isolated. According to mass spectrometry (MS) and nuclear magnetic resonance (¹H‐NMR) date, these compounds were identified as (–)‐epigallocatechin‐3‐(3‐O‐methylgallate) and (–)‐epigallocatechin‐3‐(4‐O‐methylgallate).     

Physiological function of Se‐enriched tea fertilised with sodium selenite and naturally high‐Se tea in rats

In order to increase food selenium (Se) content, Se‐enriched tea was produced by fertilising with sodium selenite in low‐Se soil. Five groups of rats were fed a low‐Se diet supplemented with either water (Se‐deficient), sodium selenite or an aqueous extraction of low‐Se tea, Se‐enriched tea or naturally high‐Se tea. The chemical form of Se in Se‐enriched tea and the physiological function in rats fed the different Se sources were determined after 8 weeks. The results showed that organic Se accounted for 80% or more of the Se in Se‐enriched tea fertilised with sodium selenite and naturally high‐Se tea, but no significant differences in the proportion of organic Se and protein Se were found between Se‐enriched tea and naturally high‐Se tea. The Se biological utilisation rates were 65.41, 68.05 and 70.49% for sodium selenite, Se‐enriched tea and naturally high‐Se tea respectively. The Se content of blood and liver and the glutathione peroxidase (GSH‐Px) activity were significantly increased by feeding Se‐enriched tea and sodium selenite compared with low‐Se tea, but a more efficient increase in liver GSH‐Px activity was obtained with Se‐enriched tea than with sodium selenite. No significant differences were found between Se‐enriched tea fertilised with sodium selenite and naturally high‐Se tea, which proved that the biological effectiveness of Se in Se‐enriched tea was higher than that of sodium selenite in increasing liver GSH‐Px activity. Se‐enriched tea fertilised with sodium selenite in low‐Se soil gave the same biological function as naturally high‐Se tea. Therefore Se‐enriched tea is a safe and effective means of increasing the Se intake of both humans and animals in low‐Se areas. © 2000 Society of Chemical Industry     

绿茶初制工艺与饮料适制性的研究

将不同品种、嫩度、加工工艺及外形制作成的原料绿茶加工成绿茶饮料，通过对绿茶汁中茶多酚、咖啡碱及儿茶素组成等主要化学成分、色差动态变化的测定和感官品质的审评以及一系列破坏性试验的研究，提出了不同绿茶加工成饮料的品质特点和一套适合绿茶饮料用的较经济合理的初制加工方法。     

Formation of 4‐hydroxynonenal (4‐HNE) in frozen mackerel (Scomber scombrus) in the presence and absence of green tea

BACKGROUND: Aldehydes are secondary lipid oxidation products formed during processing and storage of food. 4‐Hydroxynonenal (4‐HNE) is a major toxic lipid peroxidation product which has been extensively investigated in the clinical field but less so in food products. The aim of the present study was to investigate the formation of aldehydes in stored frozen fish (Atlantic mackerel, Scomber scombrus) with and without antioxidant (green tea). RESULTS: The presence of 4‐HNE in frozen fish was detected for the first time. 4‐HNE was extracted from frozen fish and identified using high‐performance liquid chromatography and liquid chromatography/mass spectrometry. The amount of 4‐HNE increased throughout storage for 26 weeks at ? 10 °C in the absence of antioxidant. A significant decrease was observed in fish samples stored at ?10 °C with green tea. Minimal amounts of 4‐HNE were formed in fish stored at ?80 °C. A similar increase in 4‐HNE was found for methyl linoleate and extracted fish oil exposed to UV irradiation. CONCLUSION: The toxic aldehyde 4‐HNE can be formed in badly stored frozen mackerel and is an indicator of reduced texture quality and nutritional value of fish. Addition of instant whole green tea as an antioxidant can provide a cheap and effective way of enhancing safety, especially in developing countries. Copyright © 2008 Society of Chemical Industry     

绿奶茶的研制

通过对茶粉的工艺条件确定，根据对活性成分、色度、溶解性、香气、滋味、价格等因素的分析，选择出最佳性能价格比的茶粉，在分析与研究现在生产工艺的基础下，复配出了性能好，价格低的稳定剂。确定了温度60—70℃，压力21MPa下均质，超高温灭菌(140℃，4s)的工艺条件。并通过反复实验确定了奶茶的配方。