Fat perception is assumed to result, at least in part, from in-mouth non-esterified fatty acids (NEFAs) detection. The aim of this study was to better understand how human oral physiology may govern the sensory sensitivity to NEFAs. For this purpose, the detection thresholds for oleic acid were determined for 17 human subjects with highly varying salivary and oral characteristics, and the thresholds were related to their oral and salivary characteristics with conventional and multidimensional data analysis. These thresholds were tested on a dairy oil-in-water emulsion that was specifically designed to avoid biases caused by differences in the initial structure of the emulsion as a function of oleic acid concentration. The emulsion was judged to be rather acceptable compared with model emulsions and commercial emulsified dairy foods. Twelve oleic acid concentrations, ranging from 0.00028% to 0.16% (w/w) in the emulsion, were tested with the ascending series three-alternate forced-choice method with nose-clips (WNC) or without nose-clips (WoNC). The oleic acid WNC and WoNC thresholds were 0.09% w/w and 0.063% w/w, respectively, and hypersensitive and hyposensitive subjects were identified. Partial least squares and analysis of variance indicated that the WNC threshold is positively correlated to both the lipolytic activity of saliva and the oral volume, whereas the WoNC threshold is positively correlated to the saliva antioxidant status and negatively correlated to its protein amount and lysozyme activity. This study supports the hypothesis that NEFAs are detected in the oral cavity in humans and provides new insights on the oral physiological characteristics that may play important roles in fat detection

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