Correlation Between Steviol Glycosides Structure And Their Bitterness/sweetness Sensory Properties

With the increasing demand of sugar reduction,high-potency sweeteners with low calorie,such as natural steviol glycosides,have become the research hotspot.However,the flavor deficiencies of these monomers limit their application.Therefore,a comprehensive and in-depth sensory analysis of steviol glycosides is essential to investigate the relationship between their structure and sweet or bitter taste,in order to further explore the co-elicitation mechanism of them.The main research contents and results are as follows:Firstly,a general sensory evaluation of six representative steviol glycosides was conducted by spectrum descriptive and time-intensity.Meanwhile,combined with the correlation models of structure and taste parameters,it showed the relationship between monomer structure and sensory performance that,less C-19 glucose substituent led to faster initial bitter stimulus(r=0.955)and the overall longer bitter taste perception(r=0.876).The more glucose substituents in C-13,the faster increase(r=0.833)and higher sweetness intensity(r=0.888)obtained.In addition,temporal characteristics of sweetness were also influenced by the ratio of glucose number at C-13 to C-19,and the higher the ratio was,the more time it would take to reach the peak(r=0.917),while the dynamic bitterness was independent of this structural factor.It was found by homologous modeling of taste receptors and molecular docking that,the more glucose groups on C-13 had stronger hydrogen bond with the sweet receptor,which could enter fast into the larger protein active-site region.Therefore,Rebaudioside M and D had a faster increase rate of sweet taste(F[5,199]=7.92,p<0.001).While the less C-19 substituents could help the molecule enter deeper bitter receptor region for tight and easy bind.This resulted in a distinct bitter taste immediately after intake(F=0.36,p=0.033)and a long duration(F=10.19,p=0.008)for both Rubusoside and Stevioside.The prediction accuracy of models may still be affected by other potential factors.From the oral adsorption and desorption experiments,it was found that the desorption percentage of smaller monomers were low(?10%),and their bitter property was largely determined by the binding degree(r_min.=0.766;r_max.=0.935),but there was no significant correlation in sweet taste(p>0.05).Then,the study on the coexistence mechanism of sweet and bitter tastes for steviol glycosides was conducted.Time-intensity was further tested by mixing six monomers with the sweet inhibitor at different concentrations.There was no significant difference in their bitterness curve profiles(p>0.05),while the release and dissipation time of sweet taste were also delayed besides the intensity was masked.The relative amount of 500 ppm for sweet inhibitor significantly reduced the area of sweetness curves(up to 30%only).This meant that the difference in the sweetness and bitterness of monomers was not due to the interaction on the signal transduction pathway after receptor activation.Molecules in the solution would bind to the corresponding taste cells respectively.These above findings provided a new way to reduce the presence of off-note.The decrease of p H significantly reduced the bitterness intensity(p<0.05)and shortened its extinction time,greatly reduced by about 40%.But the effect on sweetness intensity was less than that of bitterness inhibition,decreased by only up to 10%,and led to faster release and extinction of taste attribute(70%to 80%).Moreover,masking effect of lactic acid and tartaric acid on each monomer was prominent(p<0.001),which greatly inhibited the bitterness and often strongly weakened the sweetness.According to the comprehensive evaluation,the optimal application condition of steviol glycosides was malic acid solution at p H 4.The diversity taste perception changes were associated with oral saliva environment difference before and after acid stimulus(p<0.05).When the p H decreased,samples surface tension increased(??reached a max.about 15 m N/m),and the bitterness of the solution decreased correspondingly.At the same time,the weak gel structure of saliva was changed,the damage of reticulum layer and loss of salivary spheres made molecules unable to gather near the receptors for a long time or generate stimuli for many times.Therefore,the perception had obvious inhibitory effect on the time dimension.