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1.
Monomeric flavonoids (flavan 3-ols or tea catechins) present in Camellia sinensis leaf are transformed to polymeric theaflavin and thearubigin by oxidation occurring during tea fermentation. The distinctive colour, decreased bitterness and astringency, and characteristic flavour are derived from the fermentation process giving fermented teas a marked distinction from non-fermented green tea. Even though teas are available in many different fermentation levels from green to black, the difference in phytochemicals and volatile compounds in teas with different degrees of fermentation has not been fully investigated yet within the same tea leaf. The objective of this study was to observe non-volatile phytochemicals including polyphenolic and volatile compounds changes by oxidation under strict processing control and to evaluate the degree of fermentation for the maximum antioxidant capacity with the same tea material. Harvested tea leaf was immediately processed to different degrees of oxidative fermentation (0%, 20%, 40%, 60%, and 80%). Tea infusions brewed with each processed tea leaf were analysed for polyphenolic profile, total soluble phenolics, antioxidant capacity, and volatile profile using LC–MS, HPLC, Folin–Ciocalteu assay, Oxygen Radical Absorbance Capacity (ORAC), and GC–MS analyses. The flavonoids in non-fermented green tea were significantly lessened during the oxidative fermentation process and the decreased monomeric flavonoids were transformed to polymeric theaflavin and thearubigin as the leaves were more processed. Total soluble phenolics and antioxidant capacity were significantly higher as tea leaves were less processed with a high correlation with individual polyphenolic changes. Volatile compounds present in tea leaf were analysed by GC–MS to observe changes due to processing and were utilised to create a model to differentiate fermentation based on volatile composition. Twenty-four compounds were used to build an initial model which was optimised to 16 compounds with complete separation of the groups using discriminant function analysis. The data suggested that fermentation diminished antioxidant capacity of tea and could result in lowering potential health benefits from flavonoids. This result should be considered for tea manufacturing and the development of functional foods desiring maximum potential health benefits from antioxidant flavonoids in tea.  相似文献   

2.
红茶通氧发酵过程中发酵叶相变化分析   总被引:2,自引:0,他引:2  
潘科  沈强  申东  杜晓 《食品科学》2014,35(15):198-201
采用黔湄419、黔湄502、黔湄601、黔湄809和福鼎大白茶品种的茶青为原料,利用自制的通氧发酵装置进行通氧发酵,以自然发酵为对照;每15 min记录1次发酵叶感官品质变化情况,测定叶温及pH值。结果表明:通氧发酵处理前期叶面升温迅速且高于自然发酵叶温;明显加快发酵过程中叶面色泽的红变,促进特征香气的形成;发酵过程中,发酵叶pH值均呈降低趋势,通氧发酵处理降低速度更快;感官审评结果表明,通氧发酵样品品质整体不低于自然发酵样品。  相似文献   

3.
The current method for processing bud yellow tea usually results in astringent taste that is not sufficiently yellowing. Therefore, two factors in the production phase that affect tea quality were studied: number of times the tea leaves undergo the yellowing process and predrying of leaves to reduce their water content before a second yellowing process. We then evaluated the colour and nonvolatile compounds of the produced tea. Results revealed that gallated catechins and the polyphenol–amino acid ratio decreased significantly, and the colour of the tea changed from green to yellow after two yellowing processes. Predrying leaves to a lower water content resulted in the accumulation of free amino acids and soluble sugars, and an increase in the brightness and yellow colour of tea infusion. Bud yellow tea with the highest taste evaluation score and yellowness was obtained when the leave samples underwent two yellowing processes and the water content in the leaves was 40%.  相似文献   

4.
The design and development of a personal computer (PC) based system for monitoring changes in colour during the fermentation process that is used to produce tea is described. The technique is based on imaging the fermenting tea at different intervals of time and processing the colour images. A digital camera, together with a special lighting arrangement, was used to capture colour images during the fermentation process. The RGB colour model was used so that histogram dissimilarity measurements matched the colour of test images to a standard image colour. This dissimilarity measurement was represented by difference from the Manhattan norm (L1). The technique was compared with the visual methods used by expert tea tasters.  相似文献   

5.
为了解杜仲叶茯砖茶加工过程中挥发性成分变化,应用顶空固相微萃取(headspace solid phase microextraction, HS-SPME)结合气相色谱-质谱(gas chromatography-mass spec trometry, GC-MS)联用技术对杜仲叶茯砖茶加工过程中挥发性成分变化规律进行分析。结果表明,杜仲叶茯砖茶中共鉴定出152种挥发性成分,酸类、酯类、酮类和醇类为相对含量较高的挥发性成分,主成分分析、分层聚类分析及偏最小二乘判别分析均可直观地对杜仲叶茯砖茶不同加工阶段进行有效的区分。此外,在杜仲叶茯砖茶加工过程中,酸类、醇类、酮类和酯类等挥发性成分组成和结构发生了明显的变化,如丙酸、乙酸、2-己烯醛等具有刺激性、青辛气等不良气味的挥发性成分含量呈下降趋势,而芳樟醇、月桂酸、肉豆蔻酸、棕榈酸乙酯、菊苣酮、乙醛等具有菌花香、木香、花果香、乳香特性的挥发性成分相对含量呈上升趋势。基于VIP值筛选出64种标志差异性挥发性成分,其中,5-甲基吲哚、正三十二烷和十二醇等成分在原料中,3-氨基苯酚、环十五内酯、5-羟基-3-甲基-1-茚酮等成分在渥堆样本中,苯甲酸、4-乙烯基-2-甲氧基苯酚、1-己烯-3-醇等成分在气蒸样本中,植酮、2-吡咯甲醛和2-羟基环十五酮等成分在发花8 d的样本中以及乙琥胺、对丙基茴香醚等成分在发花25 d的样本中相对含量远高于其在其它阶段样本中的含量,这些成分可以作为杜仲叶茯砖茶对应加工阶段的候选标记物。在最终产品S5茶样中,棕榈酸甲酯、二氢猕猴桃内酯、月桂酸、植酮、β-紫罗兰酮等为相对含量较高的呈香挥发性成分,可能是构成杜仲叶茯砖茶风味特征的主要物质,这为识别杜仲叶茯砖茶的香气特征以及加工过程中香气成分的定向调控提供了基础。  相似文献   

6.
BACKGROUND: Theabrownin (TB) is a main bioactive component in Pu‐erh tea, and the total amount is between 100 and 140 g kg?1. However, reports on the mechanism of formation of TB are sparse because it has a high molecular weight and complex composition. Hence, the mechanism of formation of TB in Pu‐erh tea during solid state fermentation was investigated using an exogenous enzyme method. RESULTS: It was found that, in the presence of exogenous enzymes, the tea liquor prepared from the resulting leaves changed considerably in colour. In addition, the TB, total carbohydrate, polysaccharide, amino acid and protein contents were all increased, while the tea polyphenol content decreased sharply; the surfaces of leaves before fermentation appeared to be smooth and intact, and the structures of the cell, cellulose and lignin were complete, while after fermentation their surfaces were covered by microorganisms and the structures of the cells were largely disrupted. CONCLUSION: The enzymatic actions are closely related to the compositional changes occurring during Pu‐erh tea manufacture, and its quality. Enzymes produced by microorganisms were found to be the main cause of TB formation during the fermentation of Pu‐erh tea. Copyright © 2011 Society of Chemical Industry  相似文献   

7.
The effect of fermentation (30°, 34°, 38° and 42°C) and drying temperatures (40°, 50°, 60° and 70°C), as well as the effect of controlled drying as opposed to sun-drying on rooibos tea quality were investigated. The quality of rooibos tea improved with increasing fermentation temperature whereas quality decreased with increasing drying temperature ( P < 0.05). No significant subjective quality difference between the two drying methods was obtained. Tea dried under controlled conditions was lighter in colour than sun-dried rooibos tea ( P = 0.003) as indicated by higher L* values. The chromaticity parameters (a* and b*) were not significantly affected by drying under controlled conditions. Less chlorophyll was present in sun-dried tea than in tea dried under controlled conditions. The colour of tea prepared under experimental conditions was comparable with the colour of commercially-produced rooibos tea samples.  相似文献   

8.
Production of black tea from the same vegetatively propagated (VP) cultivars, in Kenya and Malawi, shows variations in both chemical composition and quality. Whereas it is possible to produce black teas with similar total theaflavins and individual theaflavins, brightness and total colour levels, black teas from Kenya generally have higher thearubigins, total volatile flavour compounds and flavour index. The black tea fermentation process is much faster in Malawi compared to that in Kenya, as evidenced by faster production of plain black tea chemical parameters, especially theaflavins. Consequently, in Malawi the maximum amount of theaflavins formation takes a shorter fermentation duration than in Kenya. Given ample fermentation duration, fermentation in Kenya produces a similar amount of theaflavins. This makes it necessary to optimise fermentation time, in different geographical regions even when the same cultivar is being processed. The other plain black tea quality parameters (thearubigins, brightness and total colour) were higher in black tea which was processed in Kenya than those processed in Malawi. However, the pattern in the changes in the individual theaflavins or theaflavins digallate equivalent followed that of total (Flavognost) theaflavins, suggesting that the flavan-3-ols patterns in tea leaf might not have been affected by the geographical area of production. The total volatile flavour compounds (VFC), Group I and II VFC and the flavour index were higher in black teas processed in Kenya, further demonstrating the fact that high grown Kenyan teas are more flavoury. In both Kenya and Malawi black teas, aroma quality declined with a long duration of fermentation. Short fermentation time is therefore a method of producing more aromatic black teas. The variations in black tea quality between Malawi and Kenya were possibly due to difference in environmental conditions, leading to different shoot growth rates and biochemical composition in the shoots.  相似文献   

9.
为探索不同加工工艺刺槐花代用茶主要香气成分差异特点,以新鲜刺槐花为原料,按照晒青、烘青、炒青、萎凋、发酵五种加工工艺制作刺槐花代用茶,采用顶空固相微萃取/气相色谱-质谱联用法分离鉴定刺槐花代用茶中的挥发性化合物,运用相对气味活度值ROAV评价各香气成分对刺槐花代用茶香气的贡献,以确定关键香气物质。结果表明:五种刺槐花代用茶中共检测出烯烃类、芳香烃类、醇类、醛类、酮类、酸类、酚类、酯类、内酯类、含氮化合物和杂氧化合物等75种有嗅感的挥发性成分,以醛类(16种)、醇类(12种)、烯烃类(11种)和酯类(10种)化合物为主;其中,苯乙烯、2-戊基呋喃、香芹酚、柠檬烯、苯甲醇、苯乙醛、苯乙醇、癸醛、环柠檬醛、2-苯基巴豆醛、邻氨基苯甲酸甲酯、长叶烯、棕榈酸乙酯等13种嗅感物质为共有组分,癸醛和柠檬烯2种物质为共有关键香气物质。五种不同加工工艺刺槐花代用茶主要香气成分不同,挥发性香气物质以晒青工艺最多,萎凋工艺最少。不同工艺条件下的关键风味化合物中,芳樟醇、反,反-2,4-壬二烯醛、反-2-壬烯醛是晒青工艺所特有的香气物质,萘为烘青工艺所特有的香气物质,2-甲基丁醛是炒青工艺所特有的香气物质,1-辛烯-3-醇是发酵工艺所特有的香气物质。  相似文献   

10.
酵母菌纯种发酵普洱茶初探   总被引:1,自引:0,他引:1  
酵母菌是普洱茶发酵过程中的优势菌种之一,含有极丰富的对人体有益的营养物质、丰富的酶系统和生理活性物质,此外还能代谢产生VB1、VB2、Vc等物质,是形成普洱茶甘、滑、醇品质风格的重要因子。对从普洱茶渥堆发酵样品中分离出的5株优势酵母菌进行纯菌接种发酵试验,并对发酵后的茶样进行化学成分检测和感官评价,结果发现,酵母菌株Y5能将生茶的多酚值由28.33%降至14.54%,将茶褐素值由2.45%增至6.86%,在5株酵母菌发酵的茶样中,其茶褐素增幅最为显著。另外Y5发酵的茶样有香甜味,其滋味略苦,生津,有回甘,可以用来提高普洱茶的香气和滋味。  相似文献   

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