Aplicación del modelo de Thurstone a las pruebas sensoriales de diferencia: [revisión] / Thurstone model application to difference sensory tests: [review]

En las pruebas de diferencia, el desempeño de los jueces varía en función de la prueba utilizada. Esta diferencia se explica a partir del conocimiento sobre la forma en que el cerebro procesa la información que recibe de los sentidos, particularmente el sentido del gusto. En algunas pruebas de diferencia, la información se procesa de manera más eficiente que en otras. El modelo de Thurstone describe las estrategias del cerebro para procesar la información en función del método utilizado. Esta revisión introduce las ideas y los conceptos de este modelo en las mediciones sensoriales derivadas con las pruebas de diferencia. Los conceptos de la variabilidad del estímulo y la estrategia cognitiva correspondiente a cada método de diferencia son la base para el cálculo de la magnitud de la diferencia percibida entre dos estímulos, denominada d’. Esta medición es fundamental e independiente de la metodología sensorial utilizada.

Part of understanding why judges perform better on some difference tests than others requires an understanding of how information coming from the mouth to the brain is processed. For some tests it is processed more efficiently than others. This is described by what has been called Thurstonian modeling. This brief review introduces the concepts and ideas involved in Thurstonian modeling as applied to sensory difference measurement. It summarizes the literature concerned with the theorizing and confirmation of Thurstonian models. It introduces the important concept of stimulus variability and the fundamental measure of sensory difference: d’. It indicates how the paradox of discriminatory non-discriminators, which had puzzled researchers for years, can be simply explained using the model. It considers how memory effects and the complex interactions in the mouth can reduce d’ by increasing the variance of sensory distributions.

Las pruebas de preferencia en alimentos son más complejas de lo imaginado / Food preference tests are more complex than it is thought / As provas de preferência em alimentos são mais complexas do que se imagina

Las pruebas de preferencia son ampliamente utilizadas en el lanzamiento de nuevos productos y en estudios de mercado en la industria alimenticia. Tradicionalmente se aplican a productos diferentes. Sin embargo, la magnitud de la diferencia entre los productos no siempre se evalua con anticipación a las pruebas de preferencia. Las pruebas de diferencia, a través del modelo de Thurstone, permiten estimar el grado de diferencia entre dos productos. Así, resulta interesante conocer las similitudes entre las pruebas de preferencias y las pruebas de diferencia a fín de tomar ventaja de los avances que existen en estas últimas para mejorar la utilización y aplicación de las pruebas de preferencia.

Preference tests are widely employed for launching new products and in market studies in the food industry. Traditionally, they are applied to different products. However, the magnitude of the difference among products is not always evaluated before the preference tests are carried out. Difference tests using Thurstone model allow the estimation of the degree of difference between two products. Thus, it is of interest to know the similarities between preference tests and difference tests, so as to take advantage of the advances taking place in the latter and improve the use and application of preference tests.

As provas de preferência são amplamente utilizadas no lançamento de novos produtos e em estudos de mercado na indústria alimentícia. Tradicionalmente se aplicam a produtos diferentes. No entanto, a magnitude da diferença entre os produtos não sempre se avalia com antecipação às provas de preferência. As provas de diferença, através do modelo de Thurstone, permitem estimar o grau de diferença entre dois produtos. Assim, resulta interessante conhecer as similitudes entre as provas de preferências e as provas de diferença a fím de tomar ventagem dos avanços que existem nestas últimas para melhorar a utilização e aplicação das provas de preferência.

Effect of n-3 polyunsaturated fatty acids on the lipidic profile of healthy Mexican volunteers

Objetivo. Estudiar el efecto de los ácidos grasos ponlinsaturados n-3 en el perfil lipídico sérico de una población mexicana. Material y métodos. La ingesta diaria del suplemento de aceite de salmón fue de 3 gramos durante cuatro semanas. Se evaluaron los niveles de colesterol total, triglicéridos, lipoproteínas de alta densidad y la composición en ácidos grasos de los eritrocitos. Resultados. muestran una reducción significativa (p<0.05) en los niveles de triglicéridos y un aumento significativo (p<0.01) en los niveles de lipoproteínas de alta densidad en los sujetos con hipertrigliceridemia . El grupo con hipercolesterolemia presentó reducción en los niveles de colesterol total y triglicéridos y aumento significativo en los niveles de lipoproteínas y aumento significativo en los niveles de lipoproteínas de alta densidad (p<0.01). conclusiones. El efecto hipolipidemiante de los ácidos grasos polinsaturados n-3 se puso de manifiesto en voluntarios mexicanos bajo las condiciones aquí evaluadas

Plyunsaturated fatty acid deficiencies: efects on hepatic plasma membrane fatty acid composition and enzyme activity / Deficiencias de ácidos grasos poliinsaturados: efectos sobre la composición lipídica y actividades enzimáticas hepáticas

Research on dietary polyunsaturated fatty acids (PUFA), on the activity of 5' nucleotidas and adenylate cyclase are largely contradictory due, mostly, to the absence of adequate control group. In this study, four different diets have evaluated on the 5' nucleotidase and adenylate cyclase in rat liver plasma membranes. Wistar rats were given a semysinthetic diet in which lipids were supplied by 5 porcent of either peanut oil (n-3 PUFA deficient diet), cod liver oil (n-6 PUFA deficient diet) partially hydrogenated palm oil (total PUFA deficient diet) and a mixture of peanut and rapeseed oil (control group). Liver plasma membranes were separated by using a Percoll gradiet in a Beckman JA 20 centrifuge. 5' nucleotidase and adenylate cyclase activities were measured in a liquid scintilation detector by following the degradation of 3HAMP (adenosine monophophate) and production of 3HAMP (cyclic adenonosine monophosphate) respectively. Animals fed the total PUFA deficient diet exhibited significant lower body weight and lower liver weight that did the control group. Low cholesterol concentrations were observed in animals deficient either in n-3 or total PUFA in relation to the control group. All dietary deficiencies studies provoked reduced phospholipid levels. Phosphatidylcholine and phosphatidylethanolamine were not modified whatever the deficiency studied. Phospholipids fatty acid composition was significantly modified by the diets studied. The specific activity of 5' nucleotidase in hepatic plasma membrane was independent of dietary PUFA. The catalytic unit of adenylate cyclase complex in totally deficientanimals was augmented. The unit of the enzyme stimulated by the guanydyl imidodiphosphate (GppNHp) in n-3 PUFA deficient animals was augmented and reduced in animals receiving the n-6 PUFA deficient diet. In conclusion, our results show that each dietary PUFA deficiency modifies differently the proportions of phospholipid classes and their fatty acid composition. The mechanisms responsible for these modification remain to be elucidated. However, the phospholipid fatty acid changes did not onfluence the 5' nucleotidase activity except in the case of extreme excess which concerns more toxicology than nutritional modifications. Finally, the catalytic unit (Forskoline+GDPBs) of adenylate cyclase complex and the regulatory unit (GppNHp) may be sensitive to alterations in PUFA composition