Analyse Instrumentale

[Heike Fallago]

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Objective: In the development of cosmetic products, sensory evaluation is an important step in determining consumer acceptance before it is released on a market but is often time-consuming and costly. However, correlating sensory characteristics with instrumental parameters using multivariate techniques is a potential way to facilitate the development of cosmetic products.

Methods: Sunscreen formulations varied in the content of grape seed extract (GSE) and ultraviolet (UV) filters, and benchmark products were characterized using sensory descriptive analysis and instrumental analysis. Principal Component Analysis (PCA) was applied to the panel's performance data to study how well the panelists performed compared to each other and to find an association between rheological and textural instrumental parameters of cream samples. Further, applying Partial Least Squares (PLS) regression analysis, the association between sensory attributes and instrumental parameters was analyzed. In addition, a preference for the sensory properties of the studied sunscreen products that are important for consumers living in Southeast Asia was assessed by PLS.

Results: In this study, both the sensory and instrumental properties of all tested formulations were described well by PCA. The practicality of PLS was confirmed by an established correlation between sensory attributes from the categories of appearance (glossiness), pick-up (integrity of shape, firmness, glossiness, stringiness), and after-feel (glossiness, spreadability, stickiness) with both rheological and textural parameters. Although the instrumental analysis could not completely replace sensory evaluation, a described method applying PLS can be used as an additional cost-effective and time-saving method during the development of cosmetic products. Moreover, PLS revealed that sunscreens with a light texture and glossy appearance providing smooth skin after-feel are likely to be preferred over the thicker formulations having a residual color appearance in Southeast Asia.

Conclusion: Until a universal model is created, the cosmetics developers and companies can apply a described method of determining sensory properties from the instrumental parameters of their own products. Future studies will be worth exploiting the applicability of the PLS regression model on instrumental datasets predicting sensory characteristics of other sunscreen products.

Conclusion: En attendant la cration d'un modle universel, les dveloppeurs et les entreprises de cosmtiques peuvent appliquer une mthode dcrite pour dterminer les proprits sensorielles partir des paramtres instrumentaux de leurs propres produits. Les tudes futures devront exploiter l'applicabilit du modle de rgression PLS sur des ensembles de donnes instrumentales prdisant les caractristiques sensorielles d'autres produits solaires.

Les techniques d'analyse permettant aux scientifiques de rassembler des informations quantitatives et qualitatives quant la composition et la structure de la matire ne manquent pas... Encore faut-il, face un problme concret, choisir judicieusement la stratgie adopter et exploiter au maximum les ressources qu'offre chacune de ces techniques...

L'utilisation efficace de l'instrumentation moderne d'analyse exige la comprhension pralable des principes fondamentaux la base de la technique et du fonctionnement des appareils.

C'est pourquoi cet ouvrage ralise la synthse de la pratique instrumentale tout en rappelant toutes les notions indispensables la comprhension intime des mcanismes qui sous-tendent le fonctionnement des appareils.

Ce guide indispensable met par ailleurs l'utilisateur en garde vis--vis des piges qui accompagnent toute mesure physique et lui permet de se familiariser avec les indispensables notions de limites de sensibilit, de prcision et d'exactitude des techniques.

Traduite pour la premire fois en franais par la mme quipe que Chimie analytique de Skoog, West et Holler, cette rfrence internationale parue pour la premire fois en 1971 intressera les chimistes mais aussi les physiciens, les biologistes, les agronomes, les pharmaciens, les ingnieurs, etc.

Chapitre 2 : Les composants lectriques et les circuits

Chapitre 3 : Les amplificateurs oprationnels dans l'instrumentation chimique

Chapitre 4 : L'lectronique numrique et les micro-ordinateurs

Chapitre 5 : Les signaux et le bruit

Chapitre 6 : Introduction aux mthodes spectromtriques

Chapitre 7 : Les composants des instruments d'optique

Chapitre 8 : Introduction la spectroscopie atomique

Chapitre 9 : Spectromtrie d'absorption atomique et de fluorescence atomique

Chapitre 10 : Spectromtrie d'mission atomique

Chapitre 11 : Spectromtrie de masse atomique

Chapitre 12 : Spectromtrie atomique par rayons X

Chapitre 13 : Introduction la spectromtrie d'absorption molculaire dans l'ultraviolet et le visible

Chapitre 14 : Applications de la spectromtrie d'absorption molculaire dans l'ultraviolet et le visible

Chapitre 15 : Spectromtrie de luminescence molculaire

Chapitre 16 : Introduction la spectromtrie infrarouge

Chapitre 17 : Applications de la spectromtrie infrarouge

Chapitre 18 : Spectroscopie Raman

Chapitre 19 : Spectroscopie de rsonance magntique nuclaire

Chapitre 20 : Spectroscopie de masse molculaire

Chapitre 21 : Analyse de surface par spectroscopie et microscopie

Chapitre 26 : Introduction la sparation par chromatographie

Chapitre 27 : Chromatographie en phase gazeuse

Chapitre 28 : Chromatographie liquide haute performance

Chapitre 29 : Chromatographie en fluide supercritique et extraction

Chapitre 30 : Electrophorse capillaire et lectrochromatographie capillaire

Appendice 1 : Evaluation des donnes analytiques

Appendice 2 : Les coefficients d'activit

Appendice 3 : Potentiels rdox standard et potentiels conditionnels

Appendice 4 : Composs recommands pour la prparation de solutions talons de quelques lments courants

Appendice 5 : Acronymes et sigles frquents en chimie analytique

Rponses aux problmes choisis

Index

Texture Profile Analysis is a popular double compression test for determining the textural properties of foods. It is occasionally used in other industries, such as pharmaceuticals, gels, and personal care. During a TPA test samples are compressed twice using a texture analyzer to provide insight into how samples behave when chewed. The TPA test was often called the "two bite test" because the texture analyzer mimics the mouth's biting action.

The textural identity of any food is rarely a simple matter of understanding a singular attribute such as hardness or cohesiveness. The texture of any food is multi-faceted and tied to consumers' sensory expectations. It is not sufficient to deliver a food with a target hardness and springiness value if consumers do not like it and it does not meet their expectations for that food type.

The beauty of TPA as an analytical method is that it can quantify multiple textural parameters in just one experiment. That is also the method's curse since many researchers rely on TPA's labeled characteristics without considering whether the test method provides metrics that are relevant to the experimental objective.

TPA parameters have evolved since the test's creation. Through customer feedback and extensive testing Texture Technologies has narrowed its recommended primary TPA characteristics to include hardness, cohesiveness, springiness, and resilience. Depending on the textural attributes sought after by our clients we occasionally recommend capturing either chewiness or gumminess. Adhesiveness is a popular TPA parameter, however, a TPA test technique is not always the optimal method for quantifying adhesiveness, so TPA Adhesiveness should be adopted only after careful review of its suitability as an appropriate metric (see Chapter V for more).

Dr. Alina Surmacka Szczesniak, a food scientist, principal at General Foods, and a founding editor of Journal of Texture Studies, developed the original TPA parameters as part of the sensory work she conducted in the early 1960's at General Foods' Technical Center. Dr. Szczesniak's extensive early publications focused on understanding the textural attributes that consumers experience when consuming a wide variety of food products and classifying them into metrics that could be objectively quantified with trained sensory panels. Dr. Szczesniak developed and improved sensory descriptions for the texture of specific foods while searching for more universal descriptors that could be applied across a broader array of foods. One of the goals was to develop a common lexicon and set of procedures which would allow objective, repeatable sensory texture evaluation tests to be conducted across different laboratories, operators and for many different food types.

While Dr. Szczesniak was advancing the lexicon and techniques to improve sensory texture evaluation (General Foods Texture Profile), her group was also creating an instrument (General Foods Texturometer) which could augment their sensory work and objectively quantify texture. The need for an instrumental approach was critical because, while a sensory texture evaluation was the perfect ideal, it was extremely time consuming and expensive to conduct.

Most of the instruments which substantially preceded the GF Texturometer (shear presses, gelometers, compressimeters, consistometers, tenderometers, etc.) provided single dimension values (e.g. gel strength) and did not address richer food textural characteristics that were discernable from sensory panels. The immediate predecessor, MIT's Strain Gauge Denture Tenderometer A recording strain-gage denture tenderometer for foods. I. Instrumental evaluation and initial tests. B.E. Proctor, G.J. Davison, G. J. Malecki, and M. Welch. 1955. Food Technology, vol 9:471-477.

museum.mit.edu1, was the first successful attempt to measure more than a single attribute at a time, recognizing that the texture of foods were multifaceted. Dr. Szczesniak's research group was able to show strong correlations of the GF Texturometer with sensory judgments and it was the beginning of being able to instrumentally measure more complex textural aspects of foods in an unbiased, scientific manner.

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