The Perception Of Sour Taste During Oral Processing Of Different Fluid Systems

Saliva plays an important role in food oral processing.Saliva initially helps to break down the food and form food bolus that can be safely swallowed,further influences consumer’s flavor perception of food.Taste perception during food oral processing is influenced by 1.the physical and chemical properties of the tastants and its carrier and 2.subject’s oral physiological and salivary biochemical properties.Sour taste is one of the five basic tastes,and the intrinsic and extrinsic factors that influence its perception is worth investigation.Addition of sweet tastants had been reported to affect sour taste perception in near-Newtonian fluids under static sensory evaluation.However,how sweet tastants affect sour taste perception in thickened fluids,and further,the dynamic sensory evaluation under simulated chewing conditions,is less studied.Bearing in mind of the scientific question of how sour taste is perceived during oral processing of starch-thickened fluids,this study investigated the dynamic effect of sweet tastants and fluid viscosity on sour taste perception in different fluid food systems（Newtonian and non-Newtonian fluids）and further explored their possible correlations with individual oral physiology and salivary biochemical properties.The specific research contents and main results are as follows:（1）Firstly,recruited healthy subjects were tested of their sour taste（citric acid）and sweet taste（maltose）recognition thresholds,in addition to their oral physiology and salivary biochemical properties including saliva p H,α-amylase activity and buffering capacity.Based on these factors,cluster analysis was applied to screen then classify subjects with different sour taste sensitivity and salivary buffering capacity.Seventeen subjects（8 males,9 females）further received appropriate sensory evaluation training,and 15 cm line scale sensory analysis was used to investigate the influence of individual salivary biochemical properties and sweet tastants on sour taste perception in sweet-sour solutions.Sensory results showed that:significant negative correlation between sweetness recognition threshold and salivaryα-amylase activity.Salivary p H was positively correlated with salivary flow rate and buffering capacity.The salivary buffering capacity values showed no significant correlations with taste recognition threshold,salivary flow rate,andα-amylase activity.Subjects with high sour taste sensitivity and low salivary buffering capacity reported higher sour taste intensity in sweet-sour solutions.Moreover,increased maltose concentration（sweet taste）generally enhanced sour taste intensity at the same concentration of citric acid（p<0.05）.（2）Further,two rounds of dynamic sensory analysis using time-intensity sensory evaluation（TI）were conducted in non-starch thickened（hydroxypropyl methylcellulose,HPMC）sweet-sour fluid samples to assess:1.the effect of fluid viscosity on dynamic sour taste perception and,2.the effect of sweet tastants on dynamic sour taste perception,with target shear viscosities of 80 and 380 m Pas at 50 s^-1.TI parameter differences were reflected from subjects with different sour taste sensitivity and salivary buffering capacity.The p H and shear viscosity of expectorated HPMC-thickened fluid/saliva mixture were also measured.It was observed that an increment in shear viscosity in HPMC-thickened fluid inhibited maximum sourness perception;while the addition of maltose to the fluid samples enhanced sourness perception.Subjects from different salivary buffering capacity groups and sour taste sensitivity groups showed significant differences in TI parameters(I_max,T_max,and etc.)of sour taste perception（p<0.05）.Shear viscosity of HPMC-thickened fluids was reduced after oral processing of simulated mastication.Higher concentrations of citric acid resulted in significantly higher extent of viscosity drop in thickened fluid/saliva mixtures.Similarly,the p H of thickened fluid/saliva mixture increased in all samples after oral processing,and the increment extent was dependent on citric acid concentration（p<0.01）.（3）Then,temporal dominance of sensations（TDS）and TI were used to investigate the dominance sequence and dynamic sour taste intensity perception in starch-thickened fluids,and the interpretation of sensory attribute alteration was associated with individual’s oral physiological and salivary biochemical factors.The physicochemical properties of the starch-thickened fluids were determined after oral processing.The differences in dynamic sour taste perception and physicochemical properties of the thickened fluid/saliva mixture after hydrolyzed starch-thickened fluid were analyzed across subjects with different salivaryα-amylase activity.Further,the physicochemical properties of starch-thickened fluids were compared with non-starch thickened fluids（HPMC）after oral processing.Results showed that in starch-thickened fluids,the dominant sensory attributes exhibited different time-dependent characteristics both with different shear viscosities and different citric acid concentrations.Compared to the low salivaryα-amylase activity group,subjects with high salivaryα-amylase activity perceived sweetness as dominant more often and for longer time duration.The maximum sourness intensity of the starch-thickened fluid decreased with increasing fluid shear viscosity.In terms of physicochemical properties,after oral processing,the p H of starch-thickened fluid increased,and the viscosity decreased significantly.The concentration of glucose,maltose,maltotriose and reducing sugar produced from starch hydrolysis were significantly different in different fluids and with different subjects.Meanwhile,compared with non-starch（HPMC）thickened fluid,the viscosity of starch-thickened fluid after oral processing has a significant difference.