Philippe Courcoux

Use of an experimental design approach for evaluation of key wine components on mouth-feel perception

Abstract To simultaneously explore the primary and interactive effects of proanthocyanidin (‘tannin’), ethanol, anthocyanin and wine polysaccharide concentrations on the mouth-feel perception of wine like media, a sensory study based on an incomplete factorial design was conducted. Two grape polyphenol fractions, i.e. grape seed tannins and anthocyanins, and two fractions of wine polysaccharides, (mannoproteins+arabinogalactan-proteins and rhamnogalacturonan II) were prepared and analysed. A panel of 15 trained judges generated a series of mouth-feel descriptors and rated their intensities while samples containing various levels and combinations of the components were held in mouth and after expectoration. The sensory perception was primarily determined by tannin concentration. However, the attribute ratings were also strongly influenced by all other factors both directly and through interactions. The intensities of all astringency descriptors increased with tannin concentration and were reduced when rhamnogalacturonan II was added. Bitterness increased with ethanol level and decreased in the presence of proteoglycans. Secondary effects observed included both masking and enhancement of the primary effects but also specific interaction effects. The latter are probably related to differences in the structural organization and properties of molecular assemblies involving polyphenols, polysaccharides, and ethanol.

Defining the underlying sensory dimensions

A hierarchy of three models for analysing sensory profiling data was discussed in a previous paper. The algorithm which determines the parameters of the third model has been improved and a the new version of the algorithm is presented. It is illustrated using the potatoes data proposed by the organisers of the workshop.

A polymorphism in the major immediate-early gene delineates groups among cytomegalovirus clinical isolates

Major immediate-early gene exon 4 sequences were determined at codons 161-241 and 254-397 in 25 cytomegalovirus clinical strains and compared with those of reference strains AD169 and Towne. The nucleotide sequences at codon 161-241 segregated into three groups which could be determined by restriction mapping of a 247-nucleotide amplified target. AD169 and Towne belonged to the same group. Clustered variations and group-specific amino-acid motifs found in the deduced peptide sequence of the two immediate-early (IE) exon 4 regions raised a question is to the effects of polymorphism on IE1 function and/or immunogenicity. On the basis of restriction analysis of polymerase chain reaction (PCR) products, virus isolates were also classified into four glycoprotein B (gB) genotypes. Strain distribution in IE1 and gB genotypes showed a lack of concordance of the two grouping methods, and no preferential association was observed between the clinical context or kind of specimen and IE1 or gB groups. These data lead up to further prospective studies which could provide important information on the implication of the MIE gene region in virus pathogenesis and indicate whether linkage unbalance exists in particular clinical contexts between IE1 and gB loci.

Common components and specific weights analysis performed on preference data

For the analysis of preference ratings which are presented in the form of several data sets, each data set being associated with a consumer, we run a method of analysis called Common Components and Specific Weights Analysis. This method makes it possible to determine the underlying dimensions to the preferences expressed by the consumers. Moreover, it computes for each consumer and for each underlying dimension a weight that reflects the importance that this consumer attaches to the dimension being considered. In a subsequent stage, we performed a clustering of the consumers on the basis of their agreement upon the preference dimensions.

Simultaneous decomposition of multivariate images using three-way data analysis: Application to the comparison of cereal grains by confocal laser scanning microscopy

We present a three-way data analysis method adapted to compare multispectral images such as those acquired by fluorescence microscopy. Spectral images are multivariate and can be considered as sets of pixels for which different spectral intensities have been measured. The algorithm proposed is based on the simultaneous decomposition of the covariance matrices calculated, in the present work, for fluorescence variables. This method allows the extraction of components common to each image and reveals their specificities by means of specific weights. The technique is illustrated by the analysis of microscopic image sequences acquired for five varieties of wheat and barley grains in 19 fluorescence conditions. The method made it possible to compare the fluorescence behaviors observed in the images and the strong similarities of the external tissues for the five cereals were highlighted.

Odour quality of spray-dried hens’ egg powders: The influence of composition, processing and storage conditions

This study aimed to determine whether compositional or processing parameters have an influence on the odour quality of egg powders. The parameters tested were: whole egg vs. egg yolk, polyunsaturated fatty acid (PUFA) enrichment, spray-drying temperature (160°C vs. 180°C), production scale (industrial vs. pilot plant), storage temperature (15°C vs. 30°C) and time (1, 2, 4 and 8 months). The quality of egg powders was evaluated by sensory analysis using free sorting, and by gas chromatography coupled to mass spectrometry and olfactometry. PUFA enrichment and spray-drying temperature do not affect the odour of egg yolk powders. There are significant differences between the odour of whole-egg and egg-yolk powders as well as between powders produced on an industrial scale or in a pilot plant. An increase in the odour intensity of egg powders was observed during storage, while unpleasant odours were perceived when the egg powders were stored at 30°C.

Performance indices and isotropic scaling factors in sensory profiling

Abstract A new procedure for the determination of the isotropic scaling factors in Generalised Procrustes Analysis is discussed. A noteworthy feature of this procedure is that each isotropic scaling factor is shown to be the product of a standardisation scalar which adjusts for the differences in range of scoring among assessors, and a performance index. An overall performance index for the whole panel is also discussed. The performance indices can be useful in improving the performance of the panel by pointing out whether further training is required for the whole panel or for some specific assessors. Once the isotropic scaling factors are determined, it is possible to derive a group average configuration using one of several algorithms proposed in the statistical literature which aim at matching a set of configurations by means of rotations. A data set is analysed and a simulation study is undertaken in order to demonstrate the method, and the outcomes are compared to those obtained by means of Gowers algorithm for Generalised Procrustes Analysis.

Free sorting as a sensory profiling technique for product development

Abstract The free sorting task is an efficient technique for assessing the perception of a set of products by a panel of subjects. This holistic and non-verbal task makes it possible to perform sensory evaluation with consumers and to study differences in subjects’ perception. This chapter describes different variants of sorting tasks, highlighting their advantages and limitations and presents a review of statistical methods of analysis of free sorting data. A case study in the automotive industry illustrates the use of the free sorting task for assessing the consumers’ perceptions of car body style. It shows that the free sorting task is indeed an effective tool to be used in product development.

New models for the analysis of paired comparison data; segmentation of the panel

Paired comparison experiments provide an efficient tool for the assessment of the preferences. We propose two hierarchically organised models for the analysis of paired comparison data. The first model is easy to interpret and allows straightforward ranking of the products according to the scores derived from the model. The second model is likely to lead to a better fit of the data and allows a graphical display of the products on a plane. A procedure of segmentation of the panel performing the paired comparison test is also discussed.

Optimization of Growth and Bacteriocin Activity of the Food Bioprotective Carnobacterium divergens V41 in an Animal Origin Protein Free Medium

Optimization of Carnobacterium divergens V41 growth and bacteriocin activity in a culture medium deprived of animal protein, needs for food bioprotection, was performed by using a statistical approach. In a screening experiment, twelve factors (pH, temperature, carbohydrates, NaCl, yeast extract, soy peptone, sodium acetate, ammonium citrate, magnesium sulphate, manganese sulphate, ascorbic acid and thiamine) were tested for their influence on the maximal growth and bacteriocin activity using a two-level incomplete factorial design with 192 experiments performed in microtiter plate wells. Based on results, a basic medium was developed and three variables (pH, temperature and carbohydrates concentration) were selected for a scale-up study in bioreactor. A 23 complete factorial design was performed, allowing the estimation of linear effects of factors and all the first order interactions. The best conditions for the cell production were obtained with a temperature of 15°C and a carbohydrates concentration of 20 g/l whatever the pH (in the range 6.5-8), and the best conditions for bacteriocin activity were obtained at 15°C and pH 6.5 whatever the carbohydrates concentration (in the range 2-20 g/l). The predicted final count of C. divergens V41 and the bacteriocin activity under the optimized conditions (15°C, pH 6.5, 20 g/l carbohydrates) were 2.4 x 1010 CFU/ml and 819200 AU/ml respectively. C. divergens V41 cells cultivated in the optimized conditions were able to grow in cold-smoked salmon and totally inhibited the growth of Listeria monocytogenes (< 50 CFU g-1) during five weeks of vacuum storage at 4° and 8°C.