SUMMARY The research of this thesis focused on the study of factors affecting food functional products acceptance and the development and optimization of a probiotic low-fat dairy dessert. First, the opinion of Uruguayan consumer about cheeses with different functional characteristics was studied and analysed. Conjoint analysis was used to determine the value that consumers gave to the different product characteristics such as: low-fat, salt-reduced, to be probiotic, fiber-enriched, and the type of processing, as industrial or traditional. Spreadable cheese and Dambo cheese were the two products studied. Consumer interest mainly depended on the possible health benefit of each one, and to a lesser extent, in the type of processing. In general, consumers were more interested in the regular cheese than in the functional one. However, an important group of consumers (around 40%) were interested in certain functional cheeses more than in the regular one. Among the different options, consumers considered the reduction in fat content as the most interesting. Laddering technique was used to study the reasons for acceptance or rejection of functional cheeses. In general, the main reasons mentioned by consumers to buy a functional cheese were get a better quality of life or a good body image. On the other hand, doubts about possible deficiencies in sensory quality and the distrust in the real effect of the healthier product, were the main reasons that consumers claimed for not buying cheese with a functional benefits. Secondly, the factors affecting the acceptance of a functional product just in the market, the low-fat cheese ("queso magro") of Uruguay were studied. The relationship between the sensory characteristics of six commercial samples, evaluated by a trained panel and their acceptance by consumers was determined. According to the sensory profile, Uruguayan low-fat cheeses were characterized by having a soft odor and taste, intermediate firmness, medium-high elasticity and low friability. Samples mainly differed in their texture attributes, firmness and elasticity though slight variations were observed for flavor attributes. However, flavor attributes like odor, taste intensity, bitterness and aftertaste were those that dictated the differences in acceptance. Besides the influence of the sensory attributes, the potential effect of label characteristics on the acceptance of samples was also studied. Consumers expectations generated by several labels were different. The main reason influencing the final decisions on purchasing Uruguayan low-fat cheese were the trust in certain brands or the expected pleasure based on the previous knowledge of the product or the label design. Finally, to design and optimize the formulation of a new prebiotic dairy product, the effect of inulin on physical and sensory properties and product acceptance was studied. It was observed that in presence of water long-chain inulin forms a particulate gel heterogeneous size of inulin crystals that can increase viscosity and elasticity of dairy products, but can also be responsible for a rough sensation. It was observed that the inoculation of a small amount of inulin after producing the product (seeding technique) was effective to obtain regular size inulin particles for low-fat dairy desserts. The abundance and size of the inulin particles depended on the concentration of inulin used. In this way, it was decided to develop a prebiotic and low-fat dairy dessert, using a mixture of long and short chain inulin. Response Methodology Surface was used to study the variation of rheological properties and sensory product acceptance in response to the concentration of inulin, sugar and lemon flavor. As expected, the consistency and elasticity of the product increased with the concentration of inulin and to a lesser extent, with sugar. Using scales for measuring the suitability of the intensity of sensory attributes (JAR scales), the level of consistency which consumers considered as the most adequate for the product was established. From rheological parameters, consistency index and elasticity modulus were well correlated with perceived consistency showing to be good indexes to predict the suitability of the consistency of this type of dairy products. To optimize the acceptance of the new dairy dessert the relationship between variations in composition and variation in the acceptability was studied. The level of consumer acceptance mainly varied with the concentration of inulin and sugar, and to a lesser extent with lemon flavor. According to the model obtained, the range of concentration of each ingredient for the maximum acceptability was determined (between 4 and 6.5% for inulin, between 9 and 12% for sugar and between 25 and 95 ppm for lemon flavor). To validate the new dessert, the acceptance of the product elaborated according to the formulation selected (5.5% inulin, 10% sugar and 60 ppm of flavor) was compared with the acceptance of a reference dairy dessert made with regular fat and sugar content, ?without inulin addition. Results shown that the addition of the mixture of short and long chain inulin, besides the reduction in the amount of fat, also contained less sugar (12% reduction) and less lemon flavor (60% reduction) than the reference product (regular fat content), without its acceptability degree being affected.