The Effect Of Water Quality On The Taste And Color Quality Of Keemun Infusion And Their Mechanisms

The effect and mechanism of different water quality on the taste and soup color of Keemun were studied.（1）Most Chinese people have the habits of drinking hot water and brewing tea with hot water.But the changes in the quality of boiled water have not been discussed in previous studies.In this study,43 drinking water from different brands were being assessed individually on their changes in sensory quality,pH,electroconductivity and ion content,both before and after boiling.After analysing each water sample and assessing the results,we found a correlation between sensory quality change and boil.The results showed that boiled water have relatively high softness,along with decreasing umami and irritancy taste.The pH of boiled water also increased by 0 to 2.58 which changed the electroconductivity of water.Among the samples,the electroconductivity of carbonated water decreased by 4.67±11.16μs/cm.The concentration of ions like Ca²⁺、HCO₃^-、H₂SiO₃、SO₄^2-also changed significantly:H₂SiO₃increased by 0-12.04mg/L;HCO₃^-decreased by 0-85.60 mg/L.Therefore,we infer the reduction of HCO₃^-contribute to the changes in sensory quality of boiled water.The experimental results are crucial for understanding the impact of change in the quality of drinking water after boiling,and thereby can be used as a guideline to make good use of hot water or brewing tea in daily life.（2）Analysis of the effect of 18 different drinking water on sensory quality and physical and chemical components of tea brewed Keemun found that the comprehensive sensory taste quality,fresh taste,sweet taste,bitter taste,astringent taste and comprehensive soup color quality,depth,brightness and other sensory factors in tea soup brewed with different water quality were significantly different and sensitive to water quality.The results of the analysis of the main routine physical and chemical components in tea soup showed that the changes of pH、conductivity,tea polyphenols,total amount of lutein,tea bolting,tea brown,catechin,amino acid,flavonoid glycosides,lutein,organic acid and L values in tea soup brewed with different water quality were significant.water quality is more sensitive,To some extent,the pH and electroconductivity affect the stability of the tea soup color to some extent.The water extract,amino acid,caffeine,total sugar,theophylline,theobromine,a value and b value in tea soup were less sensitive to water quality.（3）After analyzing the influence of water quality factors on the sensory quality of tea soup and the leaching correlation analysis of water quality factors in tea soup,we found that the excessive ion content and pH in water sample were unfavorable to the taste and quality of tea soup.The effect of water quality factors on sensory quality of tea soup showed that except SiO₃^2-,HCO₃^-was positively correlated with taste and sweetness of tea soup,Ca²⁺,Mg²⁺significantly positively correlated with astringency of tea soup and negatively correlated with most other ions.（4）The effect of Mg²⁺on the taste quality and conventional ingredients content of Keemun infusion were investigated,the underlying mechanism was inferred from the infusion taste differences due to different Mg²⁺concentration in solvents.The present study showed that the quality of tea infusion decreases significantly in water containing high concentration of Mg²⁺（≥16 mg/L）.As the concentraion of Mg²⁺increased,the umami taste,sweetness and bitterness of brewed tea infusion decreased,while the astringency significantly enhanced.The content of tea polyphenols,catechins,amino acids,caffeine,and Al³⁺,B³⁺,K⁺,Na⁺,S⁶⁺in the tea infusion showed a downward trend,which partially explained the causationof the decreasing trend of bitterness and umami taste of the tea infusion.Furthermore,we have found that Mg²⁺not only enhanced the astringency of EGCG,caffeine and sodium glutamate solution,but also weakens the bitterness of EGCG,caffeine solution,the umami taste of sodium glutamate solution and the sweetness of sucrose solution.The relationship between Mg²⁺and these chemical components indicated that there might be an obvious taste interaction effect among these particles;while the concentration of Mg²⁺in water increased,the turbidity of EGCG-protein mixture solution increased significantly,which confirmed the conclusion that Mg²⁺can strengthen the astringency intensity in tea infusion.The results of this study suggested that we should use water that contain relatively low concentration of Mg²⁺（≤4 mg/L）for brewing of black tea daily.（5）By analyzing the interaction effect between SiO₃^2-and the main taste sensation,we explored the internal mechanism of how SiO₃^2-affected the taste quality of tea soup was explored.The study showed that with the increase of SiO₃^2-mass concentration,the sweetness intensity of tea soup increased,the intensity of umami,bitterness and astringency decreased,and the overall taste quality of tea soup decreased.The decreased content of catechins,tea polyphenols,amino acids,epigallocatechin gallate（EGCG）and Ca²⁺,K⁺,Mg²⁺plasma leach in tea soup is the reason why SiO₃^2-leads to the decrease of taste quality of tea soup.The results showed that SiO₃^2-could enhance the taste of sodium glutamate solution and sweet taste of sucrose solution,and weaken the bitter taste of caffeine solution and the bitter and astringent taste of EGCG solution,with obvious taste interaction effect.It recommends that water containing SiO₃^2-（<48 mg/L）should be used for daily brewing of black tea.