Studies on Bitter and Astringent Taste of Tea

Bitterness and astringency are important sensory properties for evaluating quality of tea.The research advances in the mechanism of tea astringency and bitterness,astringent and bitter tasting components and their evaluations were reviewed in the present paper.The astringency arises from the interaction of salivary proteins with polyphenols which depends on the structure of both the polyphenols and the proteins.Bitter and astringent compounds in tea include phenolic acids,catechins and their oxidized products,flavonol glycosides and proanthocyanidins.There are many factors influencing on astringency and bitterness including the interaction between taste substances,repeated ingestion,saliva flow and its composition and acidity.Sensory assessment and instrumental evaluation were used in the evaluation of astringency.

Effect of Drinking Green Tea on Mental State of Humans

Tea is one of the most widely consumed beverages in the world,among which green tea is most common in China and Korea.Green tea constituents possess a great value to human health wherein lots of clinical studies and investigations were conducted by researchers and experts.However,there are still increasing demands and interest on the health properties of green tea,especially its effects on mental state of human brains.Based on the collated clinical studies,green tea was used to improve mental alertness and thinking.Thus,higher consumption of green tea was associated with a lower prevalence of cognitive impairment.This review summarizes the effects of drinking green tea on the mental state of human brains.Green tea contains a unique set of L-theanine and epigallocatechin gallate(EGCG) that possess biological activities in antioxidant,anti-memory loss,and antiproliferative assays potentially relevant to the prevention and treatment of various forms of brain damage.Theanine in green tea may play a role in reducing stress.The use of highly innovative method of reading and mental behavior of the human brain's response with the intake of green tea thru neuroimaging was also covered in this review.

Different Techniques of Screening Differentially Expressed Genes and Their Applying in Tea Plant

The genome of common varieties of tea plant,with estimated size 4000 Mb,is not clearly yet.In order to understand the gene expression difference during certain biological process,we can use transcriptome which reflects the gene expression level and is more closely related to current status instead of genome.This paper reviews several widely used techniques to screen differentially expressed genes in transcriptome level by comparing the characteristics of the methods and their application in tea plant research.

Tea Seed and Its Bioactive Functions

Tea seed is a byproduct in tea production and also a source of nutritional and bioactive compounds.There have been studies showing that extracts of tea seeds offered many physiological functions including anti-inflammatory,anti-oxidant,anti-tumor,anti-obesity,hepatoprotective and gastroprotective effects.The tea seed oil is also an acceptable biodiesel and the saponin-rich tea seed meal can be used as vermicide to expel earthworms from the soil of golf courses and sports fields.The bioactive functions of tea seed extracts and their potential uses in agricultural and industrial sectors were reviewed in the present paper.

Effects of Brewing Conditions on Quality of Pu'erh Tea Infusion

To brew tea correctly is very important to absorb the tea nutrition for people.The dynamic changes of the main compositions in brewing Pu'erh tea processing with different conditions were studied.Three different temperatures and eight times were designed to study the effects on the tea infusion quality.The index t0.5min(50%concentration of compounds in tea infusion) was used to evaluate the extract speed of compound in this experiment.The results showed that caffeine solubility speed at 80℃ was the highest to compare with tea polyphenols,amino acid,caffeine,soluble sugar,theaflavins and theabrownine,t0.5min of caffeine was 4.8 min,amino acid 10.3min was the second,the third one was tea polyphenols,soluble sugar was the lowest.We also found in different infusion temperature the t0.5min of compounds was distinguishing.With increasing the temperature all t0.5min of six compounds were shorter.However,the change regulations of t0.5min for all compounds in 90℃ and 100℃ were similar to in 80℃.Total quality score(TQS) were applied to evaluate the quality of tea infusion.The results found the TQS score of infusion was higher with the temperature rising,and the temperature to brew best quality infusion was 100℃ for 4-5min.According to the multiple regression analysis between sensory assessments and chemical components of Pu'erh tea we suggested the TQS was mainly affected by theaflavins,amino acid,soluble sugar and theabrowine four factors in 100℃.

Applications of Green Tea Extract in Bakery Products

Green tea extract(GTE) is a rich source of tea catechins with antioxidative,anticarcinogenic and antiarteriosclerotic activities and it has been applied in food such as bakery products to provide health benefits and extend the shelf life.This review outlines the stability of green tea catechins during baking process of bakery products supplemented with GTE and the effects of GTE on the functional properties,sensory properties,physical characteristics and Maillard reaction of bakery products.

Studies on Umami Taste of Tea

Umami is one of the five basic tastes and an important taste attribute of green tea.Amino acids are major components contributing to umami taste and the top three amino acids in tea are theanine,glutamic acid and aspartic acid.Trace of umami taste components adenosine monophosphate(AMP) and guanosine monophosphate(GMP) were detected in tea.Levels of umami taste components varied with tea cultivar,environmental conditions,fertilizer and processing method.The taste threshold of amino acids differentiated greatly and its DOT(dose over threshold) is an important indicator evaluating its contribution to umami taste.

Purine Alkaloids and Their Metabolism in Camellia Sinensis and Related Species

Caffeine,theobromine and theophylline are the major purine alkaloids found in Camellia sinensis.Theacrine was detected in a special Chinese tea plant named kucha(Camellia kucha).With tracer experiments,the metabolism pathway of these purine alkaloids has mostly been explored.The isolation and cloning of the genes encoding enzymes in the related pathway made it possible to develop methods to control caffeine level in tea products via transgenic technique.Further study on the kucha species would be helpful to obtain materials for processing naturally caffeine-less tea.However,there is still a long way to go in this direction such as sensory improvement of products prepared using leaves of kucha.

Advances in Genetic Transformation of Tea(Camellia sinensis)

Long-term fertility cycle,low self-compatibility and short flowering period limited the tea breeding by conventional method.It is necessary to apply biotechnology,especially genetic transformation method,to obtain new mutants and to accelerate tea breeding.This paper reviews the status and progress in genetic transformation and related influencing factors.It has been noticed that tea genetic transformation has advantages in getting useful target mutants.The genetic transformation by Agrobacterium-mediated and gene gun methods are usually used.However,further research should be focused on improvement of plant regeneration.

Preface

This issue of Journal of Tea is based on the"2013 International Symposium on Tea Science and Tea Culture"held at Shengzhou City,Zhejiang Province,China,November 28-30,2013.Tea is considered to be an important healthy drink.As an agricultural product,tea production is closely related to the bred cultivars,manuring and growing environments.As a source of functional components,tea is used as materials for extracting bioactives.Fresh tea leaves can be prepared into different kinds of tea(such as black tea,green tea or oolong tea)through