Construction Of Astringent Intensity Analysis Model Of Catechins Based On Interaction Between Polyphenols And Proteins

The perception of astringency was usually attributed to the insoluble aggregates in interacting between polyphenols with salivary protein.Turbidity measurements in vitro could quantify the degree of the complex physiological phenomena.Therefore,this formation could be used to evaluate astringency intensity of tea products with turbidity assessment.（-）-Epigallocatechin gallate（EGCG）is the mainly components contributing for the astringency of green tea infusion,turbidimetry was used to quantitatively analyze the interactions between EGCG and protein to predict the intensity of EGCG astringency.The formation of EGCG/protein complexes were measured which was expressed in terms of nephelometric turbidity units（NTU）.1.In this study,EGCG at different concentrations were mixed with mucin,amylase（spergillus oryzae）,amylase（porcine pancreas）,pepsin,BSA solutions.The interaction between polyphenols and proteins was affected by factors such as EGCG concertration,reaction time,temperature,p H,protein types,the respective reaction volume of polyphenols.Polyphenols and proteins reacted as soon as the they ontacted,and EGCG/protein complexes have the greatest precipitation near isoelectric point of protein,and low temperature promoted the interaction between polyphenols and proteins.Mucin and amylase form aspergillus oryzae were selected to build up astringency predictive models based on the relationship between the perceived intensity of EGCG and NTU values at p H 5.0,37°C,incubated 30 min in vitro assay.The predictive capacities of the models were verified by comparing the measured and predicted astringency intensity of EGCG,and mucin was more suitable for the prediction of EGCG astringency intensity in vitro.Turbidimetry can be used to determine the astringency of catechins within a certain concentration range.2.Analyze the effects of the interaction between EGCG and protein on protein structure.The fluorescence spectrum results showed the reaction occurred by means of static quenching and low temperature promoted binding.With increasing EGCG concentration,the quenching effect of both types of protein mixtures was enhanced.Synchronous fluorescence results revealed that the red-shift sensitivity between Trp and Tyr of the mixtures of mucin and amylase was different at the same EGCG concentration.The binding site of EGCG to the mucin molecule was close to tyrosine（Tyr）,and the binding site to the amylase molecule was close to tryptophan（Trp）.The results of diffusing wave spectroscopy（DWS）revealed that EGCG interacted with mucin and amylase,temperature and type of protein have a great influence on the reaction results.They had super-diffusion behavior between the two kinds of protein solutions,which changed the viscosity of the protein mixtures.3.The binding affinity of polyphenols with proteins depends on the size of the polyphenols,the greater the binding affinity will acquired when the bigger of molecules.In order to expand the scope of the predictive model,turbidity measurement was used to analyze the reactive ability between protein with four major components of catechin in green tea infusions.Researches have been showed that astringency intensity ECG>EGCG>EGC>EC under the same concentration.The turbidity measurement results were similar with it,but EGC showed the decrease of mixes’s NTU values.A pairwise interaction study was conducted,used the turbidity values of EGCG and protein solutions before reactive as a reference.The turbidity values of mixes with the addition of four kinds of catechins with the same astringency intensity changed.In general,the NTU values of the mixes were still dependent on the EGCG concentration increased.The addition of EGCG will promote the increasing of mixes NTU values,but the effect of ECG on the turbidity value was not obvious.The add of EGC and EC resulted the decrease of NTU values.The results of experimental research on monomer turbidity also show that EGC has a reducing effect on protein turbidity value,which needs further and deeper study.4.The taste of green tea infusion was the results of the interactions between various taste components,the interactions of other taste components in green tea infusion with mucin were further studied in vitro.The typical taste substances（including bitter,fresh,salty,and sweet）in green tea infusion were added to the reactive systems which include EGCG and mucin,and their effects on the NTU values of mixes between the EGCG/mucin were analyzed.The results showed that the presence of caffeine,theanine,sodium glutamate,and sucrose all reduced the turbidity value of the reactive mixture.The lower the concentration,the more obvious the effect.Other astringent substances include caffeic acid,chlorogenic acid,gallic acid,and rutin also studied here.The change of caffeic acid on EGCG/mucin mixes NTU values expressed like a wavy line,which increased firstly,and then decreased,lastly increased again.Chlorogenic acid,gallic acid,and rutin have lower astringency intensity than EGCG,after interacted with EGCG,the NTU values of the mixes could be improved.And increased with the increasing of EGCG concentration,but less than the NTU values of reference which contained EGCG under concentration which have same astringency intensity with phenolic acids.In addition,the effects of metal cations include K⁺,Ca²⁺,Mg²⁺,and Al³⁺on the NTU values of EGCG-mucin mixes were also studied.The increased NTU values Al³⁺>K⁺>Mg²⁺>Ca²⁺,Ca²⁺have little effect for EGCG and mucin interactions.The turbidity method simply and directly reflects the complexation of protein and flavor components in green tea infusion.Further studies will be performed to verify the possibility of extending the present model to green tea infusions.