Nicolas Antille

Comparison of nosespace, headspace, and sensory intensity ratings for the evaluation of flavor absorption by fat

The goal of this study was to better understand the correspondence between sensory perception and in-nose compound concentration. Five aroma compounds at three different concentrations increasing by factors of 4 were added to four matrixes (water, skim milk, 2.7% fat milk, and 3.8% fat milk). These were evaluated by nosespace analysis with detection by proton transfer reaction mass spectrometry (PTR-MS), using five panelists. These same panelists evaluated the perceived intensity of each compound in the matrixes at the three concentrations. PTR-MS quantification found that the percent released from an aqueous solution swallowed immediately was between 0.1 and 0.6%, depending on the compound. The nosespace and sensory results showed the expected effect of fat on release, where lipophilic compounds showed reductions in release as fat content increases. The effect is less than that observed in headspace studies. A general correlation between nosespace concentration and sensory intensity ratings was found. However, examples of perceptual masking were found where higher fat milks showed reductions in aroma compound intensity ratings, even if the nosespace concentrations were the same.

Reliability of Threshold and Suprathreshold Methods for Taste Phenotyping: Characterization with PROP and Sodium Chloride

The present study aimed to compare the accuracy and reliability of four standard methods used for classification of people as taster or non-tasters based on their sensitivity to PROP (6-n-propylthiouracil). A panel consisting of 21 subjects was tested for threshold and suprathreshold sensitivity of sodium chloride, PROP, and genotyped for TAS2R38. Two threshold methods, staircase and modified Harris–Kalmus, were used to obtain detection and recognition thresholds and compared for accuracy and repeatability. Similarly, two suprathreshold techniques, the just noticeable differences (JND) and the general labeled magnitude scale (gLMS), were used to determine Weber fractions and individual psychophysical functions and compared for accuracy and repeatability. Results show both threshold methods have been able to correctly separate people into two groups of tasters and non-tasters, with the staircase method having a lower variability among subjects. On the suprathreshold front, we found differences in sensitivity between tasters and non-tasters when comparing Weber fractions and psychophysical functions; however, our data suggest that clustering people without previous knowledge of their taster status is less accurate when using Weber fractions. Intensity ratings are more reliable to classify people into tasters and non-tasters. Results show that the staircase for threshold measurement and the gLMS methods are more reliable methods than Harris–Kalmus and JND for phenotyping people and can be used in large-scale studies in the quest to discover new genotype–phenotype associations.

The Global Error Assessment (GEA) model for the selection of differentially expressed genes in microarray data

MOTIVATION Microarray technology has become a powerful research tool in many fields of study; however, the cost of microarrays often results in the use of a low number of replicates (k). Under circumstances where k is low, it becomes difficult to perform standard statistical tests to extract the most biologically significant experimental results. Other more advanced statistical tests have been developed; however, their use and interpretation often remain difficult to implement in routine biological research. The present work outlines a method that achieves sufficient statistical power for selecting differentially expressed genes under conditions of low k, while remaining as an intuitive and computationally efficient procedure. RESULTS The present study describes a Global Error Assessment (GEA) methodology to select differentially expressed genes in microarray datasets, and was developed using an in vitro experiment that compared control and interferon-gamma treated skin cells. In this experiment, up to nine replicates were used to confidently estimate error, thereby enabling methods of different statistical power to be compared. Gene expression results of a similar absolute expression are binned, so as to enable a highly accurate local estimate of the mean squared error within conditions. The model then relates variability of gene expression in each bin to absolute expression levels and uses this in a test derived from the classical ANOVA. The GEA selection method is compared with both the classical and permutational ANOVA tests, and demonstrates an increased stability, robustness and confidence in gene selection. A subset of the selected genes were validated by real-time reverse transcription-polymerase chain reaction (RT-PCR). All these results suggest that GEA methodology is (i) suitable for selection of differentially expressed genes in microarray data, (ii) intuitive and computationally efficient and (iii) especially advantageous under conditions of low k. AVAILABILITY The GEA code for R software is freely available upon request to authors.

Delayed Volatile Compound Release Properties of Self-Assembly Structures in Emulsions

Temporal release and retention of aroma compounds from structured emulsions (where unsaturated monoglycerides are added to the oil) and conventional oil-in-water emulsions were studied using in vitro dynamic headspace analysis by proton-transfer reaction mass spectrometry and static headspace analysis by gas chromatography-mass spectrometry. Under dynamic conditions, the structured emulsion exhibited delayed release compared to the oil-in-water emulsion containing the same lipid content of 5%. The time to maximum concentration T max of amphiphilic and lipophilic aroma compounds increased by a factor of 1.2 (for 3 E-hexenal) to 1.9 (for octanal). The aroma release profile of the 5% lipid structured emulsion was close to that obtained for the oil-in-water emulsion containing 10% lipid. Under static conditions, the 5% lipid structured emulsion retained more of the most lipophilic aroma compounds than its counterpart 5% oil-in-water nonstructured emulsion. The present study provides potential solutions for modulating aroma release profiles of reduced-fat foods by self-assembly structures.

Rapid identification of differentiation markers from whole epithelial cells by matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry and statistical analysis

Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) was applied to identify markers for cellular differentiation. The differentiation of a human colon epithelial carcinoma T84 cell line was monitored over a period of 28 days by transepithelial electrical resistance (TER) measurements, alkaline phosphatase (AP) assay, and MALDI-TOF mass spectral fingerprints combined with statistical analysis. MALDI-MS generated specific mass spectral fingerprints characteristic of cell differentiation. Twenty-two ions were selected as diagnostic signals of fully differentiated T84 cells. Ten protein ion signals, detected by MALDI-MS and validated by statistical analysis, were proposed as T84 cell differentiation markers. Among these signals, ubiquitin was identified as a T84 cell differentiation marker by nanospray liquid chromatography/tandem mass spectrometry (nanoLC/MS/MS). Moreover, depending on the concentration of the cells seeded on the growth support, it was possible to predict the timing of the exponential phase and of cellular differentiation by MALDI-MS-derived marker ions. MALDI-TOFMS was compared to other methods for the determination of cellular differentiation: TER measurements are rapid but yield limited information as to the cellular differentiation state. AP assays are more specific for the differentiation state but take more time. By contrast, MALDI-MS has been found to be a fast, sensitive and precise method for cell differentiation assessment and provides the opportunity for multiplexing and high throughput. Moreover, the consumable costs per assay are very low.

Lipid deposition on the tongue after oral processing of medium-chain triglycerides and impact on the perception of mouthfeel.

Lipids between the tongue and palate strongly contribute to the sensory impact of a product. Mouthfeel is a sensory attribute responsible for distinguishing reduced fat from full fat food products. The aim of this work was to quantify the distribution, deposition, and retention of lipids on the tongue and palate upon oral processing and relate this to texture. The thickness of lipid deposition was measured in mouth by fluorescence. A trained panel evaluated the perceived intensity of samples to describe lipid Mouthfeel. The thickness of lipid deposition on the tongue shows spatial variation (10-100 microm) and stopped increasing after intakes higher than 8 mL of medium-chain triglycerides (MCTs). After 2 min, only 25% of the lipid deposition was retained on oral surfaces. A difference in the thickness of lipid deposition of 25 microm resulted in significantly different perception. This work describes the in-mouth behavior of food lipids and its influence on texture perception.

Influence of in-mouth aroma release on individual perception

Abstract The relationship between individual in-mouth aroma release and individual aroma perception was investigated. Large variations in aroma release between subjects exist and the question to answer is to what extent these individual differences have an impact on aroma perception. To assess this, 13 subjects performed a 3-AFC test (three alternative forced choices), while their in-mouth aroma release simultaneously was measured by proton transfer reaction mass spectrometry (PTR-MS). In each test three solutions were consumed by the panellists, two of them were the reference at 6 ppm V, one the target at varying concentrations from 6.5 to 15 ppmV. The subjects had to identify the sample of the highest aroma concentration. A correlation between individual aroma release and aroma perception could be confirmed. Higher ability to discriminate between samples of low concentration difference was found for those subjects that showed a higher in-mouth release and a lower variability.