| Bread is popular among consumers for unique flavor and excellent taste.However,eating bread will result in drastic postprandial glycemic response,which is not conducive for human dietary prevention of diabetes mellitus.Tea is beneficial to human health.In addition,polyphenols and dietary fiber of tea are abundant,which are efficient to inhabit the rate of starch digestion.Therefore,the outlook of applying tea flour to retard postprandial glycemic response of bread is wide.However,baking process is essential for bread-making,which will cause changes of tea components and further affect the inhibition effect of tea flour on starch digestion.But,pertinent studies of the effect of tea with high temperature treatment on starch digestion are insufficient.This paper studied the effect mechanism of baked black tea flour on the starch digestion by investigating the effect of water extract of baked black tea on ?-amylase and ?-glucosidase,and the absorption effect of baked black tea residue on oligosaccharides.This paper may provide theoretical reference for the development of tea black bread with low glycemic index value.Firstly,black tea was baked at 190?for 15 min to prepare water extract of baked black tea.Baking treatment was found to be an effective way to enhance the inhibition effect of black tea on both ?-amylase and ?-glucosidase,and IC50 of water extract of baked black tea(BBTWE)were 1.213 mg/mL and 4.190 mg/m L,respectively,while IC50 of water extract of black tea(BTWE)were 1.723 mg/m L and 6.056 mg/mL,respectively.This paper studied the change of tea polyphenols of black tea during baking.Results showed that the content of total polyphenols,theaflavins,thearubigins,and theabrownins all decreased during baking,while the content of epigallocatechin increased.Secondly,this paper further studied the effect mechanism of water extract of baked black tea on ?-amylase and ?-glucosidase using synchronous fluorescence.Results showed that the red shift of synchronous fluorescence spectra(??=60 nm)of ?-amylase and ?-glucosidase induced by BBTWE was more than that induced by BTWE,while the red shift of synchronous fluorescence spectra(??=15 nm)of ?-amylase and ?-glucosidase induced by BBTWE was less than that induced by BTWE.Therefore,baking treatment intensified the interaction between water extract of black tea and tryptophan residues of ?-amylase and ?-glucosidase,but weakened the interaction between water extract of black tea and tyrosine residues of ?-amylase and ?-glucosidase.The quenching mechanism between BBTWE and ?-amylase or ?-glucosidase was static quenching type,which was same to BTWE.Thirdly,the absorption effect of baked black tea residue(BBTR)on oligosaccharides,starch digestion products,was studied.Results showed that BBTR significantly absorbed glucose and lactose when BBTR concentration was more than 2.8 mg/mL.While BBTR significantly absorbed maltose and dextrin when BBTR concentration was more than 8.0 mg/m L.The absorption effect of BBTR on sucrose gradually decreased as the diffusion time increased.Fourthly,the effect of black tea flour on starch digestion of bread was studied by vitro digestion assay.Results showed that black tea flour significantly inhibited starch digestion of bread(P<0.05),and the inhibition rate was positively correlated with addition amount of black tea flour.Lastly,the effect of black tea flour on bread quality was studied.Results showed that adding black tea flour(0~5%)increased the storage modulus,loss modulus and extension curve area,while decreased the extension of dough,which suggested that black tea flour intensified gluten network and decreased extensibility.In addition,adding black tea flour made bread pore become more small and compact.When the addition amount was more than 4%,pore area fraction,specific volume,cohesiveness and resilience of bread significantly decreased(P<0.05),and the sensory evaluation score of bread decreased.Therefore,the appropriate addition amount of black tea flour was no more than 4%. |
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