| In the process of the food oral processing,consumers' perceptions to the food texture is considered to be a multi-dimensional dynamic feeling.It can be effectively and accurately described by traditional rheology and tribology.However,the current research on "oral" tribology is more focused on in vitro simulation studies,there is few researches which have established an equipment to measure the real oral friction coefficient.This study aims to establish a method for measuring in situ oral friction coefficient.The feasibility and reliability of the method are verified by method of hard tribology,soft tribology and pig's tongue which is used to simulate human tongue to measure the friction coefficient.At the same time,this experimental method was also used to study the oral friction coefficient between different time and lubrication,and connection with the food sensation.The main research contents and conclusions are as follows:(1)Establish the in situ oral lubrication measurement,by using the texture analyzer and iowa oral performance instrument(IOPI).And the friction force was measured by texture analyzer in real time,while the tongue muscle instrument can record the real-time pressure between the tongue and palate,then the ratio of them is the friction coefficient.In this experiment,using hard tribology to measure the friction coefficient of the same plane under different pressures,the result showed there was no significant difference in the friction coefficient of the rough glass under different pressures.Therefore,it proved that the method is feasible.Next,by using the more mature soft tribology method and the pig's tongue simulation measurement experiment,the same four food samples(Mengniu pure milk,Yili vanilla ice cream,Arowana corn oil and Nestle coffee)were measured,and the results of the frictional properties were relatively consistent,both lubricating properties:corn oil>ice cream>milk>coffee.This was also proved when the fat content is higher,the lubricating properties will be better.All of these experiments proved that the established in situ oral friction measurement method was reliable.(2)Using the established in situ oral friction measurement method to study the friction coefficient during different time(10:30 am and 3:30 pm).The oral friction coefficient was measured and compared with the saliva flow rate,shear viscosity and total protein content of the saliva in the same time.The results are as follows:The oral friction coefficient during morning and afternoon maybe increasing or decreasing.Further correlation analysis was carried out with the results of volunteers' saliva flow rate,total protein content and shear viscosity.It was found when the saliva flow rate and total protein content were stable,there was a significant negative correlation between shear viscosity and the oral friction coefficient of volunteers(p<0.05).The difference of the friction coefficient between morning and afternoon was mainly related to the changes of the total protein content and shear viscosity.(3)Using the established in situ oral friction measurement method to study the friction coefficient under different lubrication.The oral friction coefficient of milk,ice cream,coffee and 1 g/L catechin and tannic acid solution was measured and compared with their soft tribology results.Sensory evaluation experiment of food samples was conducted.The experimental results are as follows:the lubrication ability obtained by the in situ oral lubrication measurement method is basically the same as the soft friction measurement,ice cream>milk>coffee.After drunk tannic acid solution,the real friction coefficient was significantly higher than others,it's related to the astringency sensation,and correlation between astringency and friction coefficient was higher(R2=0.89).The sensory evaluation experiment also proved the correlation between the feeling of fat and friction coefficient,and found that the fat content,the slippery and the friction coefficient at 1 mm/s had a good correlation(p<0.05). |
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