绿茶浓缩汁中不可逆沉淀形成的研究

为研究绿茶浓缩汁中不可逆沉淀的化学组成及其形成过程,本文分析了茶浓缩汁中不可逆沉淀与可逆沉淀的主要化学组成,及低温条件下不同贮藏阶段(0~20 d,20~180 d,180~250 d)不可逆沉淀与可逆沉淀的形成情况。研究结果表明,不可逆沉淀含有大量金属元素和草酸根离子,而可逆沉淀主要由茶多酚、碳水化合物、咖啡碱、蛋白质及黄酮化合物组成;浓缩汁沉淀以可逆沉淀为主,不可逆沉淀较少;随着贮藏时间延长,沉淀量逐渐增加,但大部分可逆与不可逆沉淀都在0~20 d形成;元素Mg、Mn、Ga、Ni和Zn主要是在0~20 d参与不可逆沉淀形成,Fe和Cu主要在20~180 d,而Al和Ca主要是在180~250 d。另外,本文还验证了鞣花酸能与蛋白质结合产生不可逆沉淀。本文结果说明绿茶浓缩汁不可逆沉淀主要是不溶性草酸盐。     

浸提时间对绿茶茶汤沉淀形成的影响

比较了不同浸提时间(5～60min)对绿茶茶汤主要理化成分及可逆与不可逆沉淀量的影响。研究结果表明,随着浸提时间的延长,绿茶茶汤固形物浓度、主要化学成分含量、可逆沉淀量及不可逆沉淀量都呈逐渐增加的趋势;浸提5～40min,茶汤中主要化学成分含量和茶汤沉淀都显著增加;浸提时间超过40min后,茶叶中主要化学成分的浸出达到动态平衡,茶汤固形物浓度和茶汤沉淀都处于相对稳定状态。选择绿茶茶汤浸提时间40min,可以获得有效成分的最大浸出量。     

浸提茶叶质量浓度对绿茶茶汤沉淀形成的影响

比较了浸提茶叶质量浓度对绿茶茶汤主要理化成分含量及可逆与不可逆沉淀形成量的影响。研究结果表明,随着浸提茶叶质量浓度的升高,绿茶茶汤固形物浓度,主要化学成分含量,可逆沉淀量及不可逆沉淀量都显著增加;随着浸提茶叶质量浓度的升高,茶叶中可溶性物质浸出率下降,但是随着茶汤中固形物含量上升,相同单位浓度下产生的沉淀量增加。较低的茶叶质量浓度更有利于获得较高的得率和较少的沉淀。0.1 g/m L茶叶质量浓度可能是个临界点,更高的茶叶质量浓度不利于茶叶有效物质浸出,且容易产生沉淀。     

绿茶饮料沉淀机制及澄清技术

绿茶饮料的加工技术中仍存在保色、保香和防沉淀等关键问题有待解决,其中沉淀现象是目前制约绿茶市场发展的重要因素之一。由于冷后浑的形成,茶汤性状不稳定,不能保持清澈透明的饮料特征,或在储藏过程中会逐渐形成沉淀;在茶饮料生产过程中,需采用各种方法去除冷后浑或阻止冷后浑的形成,以保障产品的澄清透彻。本文从参与绿茶饮料沉淀的主要生化因子(茶多酚、蛋白质、咖啡碱、金属离子)出发,深入探讨了茶多酚与蛋白质、茶多酚与咖啡碱、茶多酚与金属离子之间的络合机制;从物理法、化学法和生物法三个方面综合概述了绿茶饮料当前主要采用的澄清技术,并根据沉淀机制对绿茶饮料可行的澄清技术提出展望。     

花香绿茶饮料的生化成分变化及物性特征

研究以花香绿茶为原料的茶饮料在高温灭菌前后及分别在37 ℃和4 ℃条件下贮藏7 d后,茶汤色差、透光率、粒径、沉淀量和沉淀微观结构以及茶多酚、氨基酸、蛋白质、黄酮、水溶性总糖、咖啡碱和儿茶素组分常规化学成分含量的变化规律。结果表明：1）4 ℃贮藏在一定程度上可有效缓解茶饮料色泽的劣变和保持较好的澄清度,37 ℃贮藏则加速汤色黄化和浑浊;2）不同的贮藏方式对生化成分含量的影响差异显著,4 ℃贮藏能够保持较高的生化成分含量,37 ℃贮藏易使品质风味显著劣变,生化成分含量显著减少;3）4 ℃贮藏生成的沉淀量要比37 ℃贮藏少,4 ℃贮藏生成的沉淀由许多小分子颗粒聚集而成,而37 ℃贮藏生成的沉淀则是由大块的分子团聚集而成。     

温度和糖度对金丝小枣浓缩汁贮藏稳定性的影响

以产于山东省乐陵市金丝小枣的浓缩汁为试材,研究了不同糖度浓缩枣汁在不同条件贮藏过程中的浊度、活性蛋白(HAP)、Vc、Chroma值和L*值的变化,探讨了温度和糖度与浓缩枣汁贮藏稳定性的关系。结果表明:4℃是保持金丝小枣浓缩汁贮藏稳定性、色泽和营养成分等贮藏品质及浑浊和沉淀出现时间的理想温度;70°Brix金丝小枣浓缩汁在不同温度下贮藏的效果均优于50°Brix和60°Brix枣汁,色泽变化相对较小,出现浑浊和沉淀的时间较晚。     

浸提方式对绿茶沉淀胶体特性与理化组成的影响

为探究浸提方式对绿茶沉淀形成的影响及其可能机制,本研究采用微波、超声波、水浴浸提云南大叶种绿茶,利用动态光散射等技术分析茶汤胶粒与沉淀颗粒的胶体特性,利用高效液相色谱等技术测定其理化组成,利用逐步回归法分析各组分沉淀浓度与茶汤浓度的线性相关性,发现:微波浸提茶汤胶粒数目仅约为沸水浴的57%,但其沉淀总量、总沉淀率均显著高于后者,微波浸提绿茶沉淀总量主要与茶汤酯型/非酯型儿茶素、酯型儿茶素/生物碱比例呈显著正相关(R2为0.972),而水浴浸提绿茶沉淀总量与茶汤生物碱浓度呈显著正相关(R2为0.969);超声波浸提显著降低茶汤胶粒与沉淀颗粒直径,但其沉淀总量、总沉淀率均与水浴浸提相当,且沉淀总量仅与茶汤蛋白质、生物碱浓度呈较弱正相关(R2为0.632)。浸提方式不仅影响绿茶沉淀胶体特性与理化组成,并可能改变沉淀形成的量效机制。     

乳清中β—乳球蛋白的高压优先水解

蛋白质在1000～3000大气压下,有时发生可逆的变性、解离或沉淀,而高压的影响多为不可逆。要使高压对蛋白质产生可逆影响,需要采用酶法为蛋白质变性以便保留某种蛋白质而清除另一种蛋白质。例如,婴儿食品变性乳添加剂的浓缩物就是选择性地从浓缩猪乳清中消除β-乳球蛋白,保留α-乳球蛋白。     

休闲豆腐干贮藏过程中品质变化研究

以休闲豆腐干为研究对象,在常温下贮藏180d,利用感官评价和热量成分检测仪、质构仪等快速检测手段研究休闲豆腐干货架期内品质变化。结果表明:随着贮藏时间的延长,豆腐干品质越来越差;60~90d是豆腐干品质微变时期,营养组分和质构特性变化小,90~180d是其品质显著变化时期,水分含量骤减,蛋白质、脂肪含量显著升高,碳水化合物含量持续下降;硬度、咀嚼性、粘聚性显著增大,回复性下降。主要营养物质含量变化是引起豆腐干质构特性变化的主要原因。并确定硬度和咀嚼性是贮藏过程中影响豆腐干品质变化的关键指标。建议豆制品企业将豆干保质期定为120~150d。     

木瓜蛋白酶（酶清）在啤酒工业中的应用

啤酒的冷混浊聚合物主要是蛋白质、多酚,在0℃~-3℃形成,此混浊沉淀属可逆性;而蛋白质、多肽与多酚氧化形成的混浊沉淀基本上是不可逆的。     

Irreversible sediment formation in green tea infusions

The formation of irreversible tea sediment (IRS) and its chemical components in green tea infusions were investigated. The results showed that the amounts of IRS in the green tea infusions from various tea cultivars ranged from 0.10 to 1.47 mg/mL. The amount of IRS was influenced remarkably by the chemical components in the green tea infusion. Principal component analysis and regression analysis indicated that gallated catechins, Mn, Ca, caffeine, Na, and (-)-gallocatechin gallate (GCG) were the principal components. IRS (mg/mL) = -4.226 + 0.275 gallated catechins + 79.551 Na + 7.321 Mn + 21.055 Ca + 0.513 caffeine - 0.129 GCG (R2 = 0.697). The contents of the main chemical components in the reversible tea sediment (RTS) and IRS were markedly different, especially the minerals. Large amount of minerals participated in the formation of irreversible green tea sediment. The amount of IRS increased with the extraction temperature.     

蔗糖对绿茶饮料理化成分及其风味稳定性的影响

绿茶饮料的风味稳定性一直是制约高品质绿茶饮料货架期的技术瓶颈。为了提高绿茶饮料的风味稳定性,分析比较了绿茶加工过程中不同蔗糖添加量(0,1%,2%,4%和8%)对绿茶饮料灭菌(135℃,15 s)、贮藏(4,25,38℃;0~60 d)过程中感官品质以及理化成分的影响。结果表明,与对照(未加蔗糖处理)相比,添加蔗糖使绿茶饮料滋味更鲜爽甜醇,香气浓度增加;灭菌后,添加蔗糖使得绿茶饮料的香气和滋味品质提高,总儿茶素和表型儿茶素含量增加,非表型儿茶素下降;在不同贮藏条件下,相比对照,添加蔗糖后的绿茶饮料风味品质有明显改善,包括汤色亮度增加,香气和滋味增强,茶多酚、氨基酸、咖啡碱以及儿茶素含量均有所增加,在贮藏42 d内添加蔗糖对绿茶饮料风味品质稳定性的提高更为明显,且2%和4%蔗糖添加量对绿茶饮料的风味品质有更好的改善作用。研究结果表明在一定的贮藏条件下,绿茶加工过程中添加蔗糖可以较好地改善绿茶饮料的风味品质并保持其稳定性。     

不同茶饮料贮藏过程中品质的变化

本文从色泽、浊度及活性成分含量三个方面分析不同茶饮料的品质变化特征，分别对高酸绿茶饮料、低酸绿茶饮料、高酸红茶饮料及低酸红茶饮料在不同贮藏条件下的可溶性固形物含量、透光率、浊度、色差、茶多酚含量、表没食子儿茶素没食子酸酯（Epigallocatechin gallate，EGCG）含量等指标进行测定，探究不同茶饮料在不同贮藏条件（温度、时间）下品质变化的情况。结果表明:不同茶饮料在贮藏过程中，透光率无显著变化；高酸绿茶饮料在4 ℃及25 ℃条件下贮藏，随贮藏时间的延长，浊度显著增加，贮藏至第180 d，分别增加了52.04%、34.12%，红茶饮料浊度无显著变化；不同茶饮料在贮藏过程中，随贮藏时间的延长，L*值降低，a*值及b*值增加，25 ℃条件下贮藏至180 d，高酸绿茶饮料、低酸绿茶饮料、高酸红茶饮料及低酸红茶饮料的L*值分别降低了31.86%、39.98%、30.22%及37.73%；茶饮料中的茶多酚及EGCG含量随着贮藏时间的延长而降低，EGCG降解程度较茶多酚高，在55 ℃条件下贮藏15 d，高酸绿茶饮料、低酸绿茶饮料、高酸红茶饮料及低酸红茶饮料的茶多酚含量分别降低9.08%、10.28%、13.39%及18.63%，EGCG含量分别下降了35.32%、42.18%、47.22%及49.03%。     

茶多酚、抹茶对鲜湿米粉储藏过程中老化行为与消化性能影响的研究

探究了茶多酚、抹茶对挤出型鲜湿米粉在180 d储藏期内老化行为和消化性能的影响。结果显示,添加茶多酚与抹茶均能显著降低鲜湿米粉的硬度,抑制老化程度。在室温环境中,茶多酚在储藏前期(0~60 d)抑制鲜湿米粉老化的效果较为显著,而抹茶在储藏中后期(90~180 d)的效果较好;在4℃冷藏环境中茶多酚与抹茶的老化抑制效果受到限制,不同种类鲜湿米粉老化程度接近。与对照鲜湿米粉相比,添加茶多酚与抹茶均能提高鲜湿米粉的慢消化成分(slowly digestible components,SDC)和抗消化成分(resistant components,RC),其中茶多酚的效果更为显著。在室温和4℃储藏过程,茶多酚与抹茶对鲜湿米粉中RC含量增加起到了显著的作用,为营养健康鲜湿米粉的创制提供了基础数据。     

Effects of rosemary and green tea extracts on frozen surimi gels fortified with omega‐3 fatty acids

Two different sources of omega‐3 fatty acids (fish oil concentrate and menhaden oil) with or without the addition of natural antioxidants (rosemary and green tea) were incorporated into surimi gels at equivalent levels and examined for changes in sensory and physical properties and resistance to oxidation during 9 months of frozen storage. Gels with menhaden oil showed higher acceptance than gels with fish oil concentrate, which displayed a fishy taste that was partially masked by natural antioxidants. Formation of volatile compounds was similar in all samples. Upon heating to form the gel, there was a ca 20–25% decrease in the relative polyene index of the control containing no rosemary or green tea extract. Formulations with menhaden oil containing green tea and rosemary were more stable immediately after cooking; however, a slight pro‐oxidant effect occurred during storage. Omega‐3 fortified gels were whiter than gels with no added oil. Rosemary and green tea extracts increased yellowness (b*) and redness (a*), respectively. Strength increased in all formulations during frozen storage. Copyright © 2005 Society of Chemical Industry     

绿茶提取液沉淀形成机理的研究

以绿茶为试验材料,从茶汤体系的物化性质和化学成分两方面探讨了茶汤沉淀形成的机理。通过对沉淀形成过程中沉淀颗粒形态变化、电解质和氢键裂解剂的作用、红外光谱变化等内容的研究,来判断茶汤形成沉淀前后的性质改变,初步判定经低温贮存后的茶汤体系介于胶体分散系和粗分散系;茶汤颗粒间的氢键、静电作用是影响茶汤沉淀形成的因素,共价键不是沉淀形成的主要因素。通过计算茶汤中各主要成分进入上清相和沉淀相的分配系数,来判断该成分进入上清相和沉淀相的趋势,结果表明:茶多酚是构成茶汤沉淀物的主体物质,其次是果胶、咖啡碱,而在沉淀相中分配系数较大的成分依次是叶绿素、没食子酸、果胶、蛋白质、花青素、咖啡碱、可可碱。     

Effect of tannase treatment on protein-tannin aggregation and sensory attributes of green tea infusion

Effect of tannase enzymatic treatment on protein-tannin aggregation and sensory attributes of green tea infusion was investigated. Green tea leaves were extracted with hot water at 85 °C for 20 min, the tea infusion was then treated with tannase. Results showed that both EGCG and ECG of the tea catechins were hydrolyzed by tannase into EGC and EC, respectively, accompanied by production of gallic acid. The tannase-treated tea infusion had a relatively lower binding ability with protein. Changes in the content of tea catechins, formation of tea cream, and turbidity of tea infusion with or without tannase treatment were measured after 4 weeks. Content of catechins in the tannase-modified tea remained almost unchanged, while those without tannase treated (control) decreased significantly (p < 0.05). Meanwhile, better color appearance and less tea cream formation were observed for the tannase-treated green tea, and tea cream formed for the control after storage. Results of the sensory evaluation showed that mouth feeling, taste and the overall acceptance of the tannase-treated green tea infusion were all better than those of the control.     

基于滋味和香气成分结合化学计量法鉴别不同贮藏年份的康砖茶

本研究以不同贮藏年份康砖茶为试验材料,测定其主要的滋味成分和香气成分,初步明晰贮藏过程中滋味成分和香气成分的变化规律,通过化学计量学方法,客观地鉴别不同贮藏年份康砖茶的滋味特征和香气轮廓。结果表明：康砖茶滋味和香气对贮藏时间有明显的响应。茶多酚、儿茶素组分、没食子酸、咖啡碱、可溶性总糖和和葡萄糖含量在贮藏期1~10年间降低,在之后的10~30年间增加。茶褐素和麦芽糖含量在贮藏期1~30年间显著增加（p<0.05）。构成香气轮廓的特征挥发性成分数量先减少后增加,酯类和杂环类逐渐取代不饱和醛类、醇类和酚类成为康砖茶的重要赋香成分。基于贮藏期的康砖茶滋味特征和香气轮廓的变化规律,滋味特征分为1~6年、10~15年和22~30年;香气轮廓分为1~6年、10~22年和25~30年。贮藏期10年是滋味特征和香气轮廓从新茶向陈年老茶转变的转折点。因此,基于滋味成分和香气成分结合化学计量学对不同贮藏年份康砖茶的品质特征进行鉴别是可行的,滋味特征和香气轮廓的变化规律可作为康砖茶价值评价的重要依据。     

Effect of selenium spraying on green tea quality

This research was conducted to determine the effects of different selenium treatments on the sensory and chemical qualities of green tea harvested in the summer tea‐producing season. Green tea was produced from fresh tea leaves sprayed with sodium selenite or organically bound selenium solution. The results showed that the sweetness and aroma of green tea extracts were significantly increased and the astringent taste and bitterness were significantly reduced by selenium spraying during the summer tea‐producing season. Significant differences in astringent taste, bitterness and sweetness of green tea extracts were found between sodium selenite and organically bound selenium treatments. The total amino acid and vitamin C contents of green tea were significantly increased and the ratio of polyphenols and amino acids was significantly decreased by selenium spraying. The vitamin C content of green tea during storage was more stable as a result of selenium treatment. No significant difference was found between sodium selenite and organically bound selenium treatments. These results demonstrate that the sensory and chemical qualities of green tea were significantly improved by selenium spraying. © 2001 Society of Chemical Industry     

水分活度对碧螺春绿茶贮存稳定性的影响

以碧螺春绿茶为实验材料,研究水分活度对绿茶贮存稳定性的影响.结果表明,水分活度对绿茶的贮存稳定性有很大的影响.不同水分活度下贮存4个月后,在高水分活度区域,绿茶的稳定性显著下降,各生化成分含量迅速降低.在低水分活度区域,碧螺春茶相对稳定,但脂质、咖啡碱、儿茶酚等成分含量的保留值小于A叫0.33处.碧螺春绿茶在Aw0.2～0.3范围内(单层水分含量对应范围)具有最佳稳定性.