Effects Of Capsaicin On Tongue Surface Temperature And Tactile Sensations As Well As Food Texture Sensory Evaluation:A Pilot Study

Spicy food is one of the most popular foods around the world.The foods like Sichuan cuisine,Indian curry,Tom Yum Goong soup and Italian spicy pizza are typical representatives of spicy food.According to a survey,about one fifth of population in China have a preference for spicy food,especially in Sichuan,Guizhou,Chongqing and Hunan province,chili pepper is a kind of indispensable kitchen seasoning for cooking.When consuming spicy food,the human body is usually going to feel that their oral cavity is heated,but this subjective feeling lacks experimental evidence due to technical limitations or other reasons.In addition,during food oral processing,the effects of capsaicin from spicy food on food texture sensory evaluation cannot be ignored,but few literature reported.In this thesis,effects of capsaicin on tongue surface temperature and tongue surface tactile sensation were studied and effects of capsaicin on food texture sensory evaluation were also researched.The main contents and conclusions of this thesis are as follows:(1)An infrared imaging technique has been investigated as a novel,real-time,non-contacting and non-invasive method for tongue surface temperature measurement.The circadian rhythm of tongue surface temperature was observed by this method.The effects of physical factors(water of different temperatures)and chemical factors(capsaicin solutions of different concentrations)on tongue surface temperature were also measured by means of this method.Finally,the method was also applied to validate temperature measurement during food oral processing.The results showed that the infrared thermal imager could measure tongue surface temperature quickly and accurately.It was found that circadian rhythm of tongue surface temperature showed a good consistency with the circadian rhythm of sublingual temperature.After rinsing with water of different temperatures,the tongue surface temperatures changed accordingly;Treatment of capsaicin solutions also led to an increase of tongue surface temperature.The feasibility of this method was further confirmed by chewing gum test.(2)Semmes-Weinstein monofilament,Bio-Thesiometer and Touch-Test(?)Two-point discriminator were applied for the threshold measurement of light touch,vibration perception,and two-point discrimination on tongue surface,respectively.The effects of the capsaicin and the temperature on the tactile sensation of tongue surface were respectively studied.The results showed that the capsaicin solution had no significant impact on the tactile sensitivity of the tongue.However,tongue surface temperature significantly affected vibratory perception threshold(P<0.05),though it had little effect on light touch and two-point discrimination thresholds.As the tongue surface temperature increased,the vibratory perception threshold gradually decreased.(3)The effects of capsaicin on the sensory evaluation of food texture characteristics,such as shear viscosity and particle size,have also been investigated.In addition,correlations between shear viscosity discrimination and vibratory perception as well as correlations between particle size discrimination and lingual tactile sensations have also been established.The results showed that JNDs(Just Noticeable Differences)of discriminating shear viscosity in control and experimental group were found to be 34.71%and 20.50%,respectively,which indicated that capsaicin could make the oral cavity more sensitive to viscosity changes.The JNDs of discriminating shear viscosity after rinse with water of 0,20,37 and 45 ? were 41.34%,34.71%,28.08%and 23.13%,respectively,which indicated that a higher oral temperature would improve the capability of shear viscosity discrimination.The effect of oral temperature on shear viscosity discrimination was consistent with that of oral temperature on the vibratory perception threshold.Therefore,we speculated that vibratory perception may play a major role in shear viscosity sensation and discrimination.However,it seemed that particle size discrimination of human tongue was not affected by capsaicin treatment.According to regression analysis,there was a positive correlation between shear viscosity and vibration perception threshold but no direct correlation between particle size and light touch,vibratory perception and two-point discrimination thresholds.