THERMOPHYSICAL PROPERTIES OF COCONUT WATER AFFECTED BY TEMPERATURE

The effect of temperature on the thermophysical properties of coconut water was investigated from 5 to 80C, taking density, Newtonian viscosity, thermal diffusivity and thermal conductivity into consideration, besides specific heat. The validation of existent models of other foodstuffs, as well as the proposal of new models, was also investigated. It was verified that temperature significantly affected these properties, presenting in general a linear behavior, except for Newtonian viscosity, which presented an exponential behavior. Among the existent equations, results from the multiple linear model were appropriated to predict the density, thermal diffusivity and thermal conductivity values, while the model, which depended on solids fraction, was the best one for specific heat value, and the exponential model was the best in relation to Newtonian viscosity values. The proposed models fitted well, and were simple and easy to use.

PRACTICAL APPLICATIONS

Most of the known values of thermophysical properties of fluid foods typically concern products from subtropical and cold areas. Until today, there was little information concerning tropical products such as coconut water. Food composition and temperature are important factors that affect thermal properties. In order to create and adapt specific equipment, optimize processes that involve pumping and heat transfer, contributing to an effective design of food-processing equipment for tropical fluid foods, it is important to know the factors. Besides, the evaluation of existent models and equations, and the introduction of new equations is important to allow an adequate prediction of studied properties, thus saving time, material and money.     

RHEOLOGICAL PROPERTIES AND FLUID DYNAMICS OF COFFEE EXTRACT

The rheological behavior of coffee extract with different water contents (49 to 90%) was studied at a wide range of temperatures (274 to 365 K) using a concentric cylinder rheometer. The flow curves followed different models depending on the concentration and temperature level. Newtonian behavior was observed at high values of water content and temperature, changing to power law as these values were decreased. The Newtonian viscosity as well as the consistency and behavior index could be well correlated by functions simultaneously dependent on temperature and water content. The rheological parameters, together with experimental values of pressure loss in tube flow, were used to calculate friction factors. These showed to be in good agreement with those resulting from classical theoretical and empirical equations, thus confirming the reliability of the rheological measurements.     

TRANSIENT NATURAL DRYING-INDUCED BOUNDARY LAYERS

ABSTRACT

This work presents a methodology far obtaining heat and mass transfer coefficients for problems involving natural convection along a flat plate. In order to simulate drying conditions, a set of data has been obtained for the temperature range between 20 and 98° C and for various absolute humidities, both of the wall and ambient. It is shown that for drying at temperatures above 80° C, Nusselt and Sherwood numbers change very appreciably with respect to values obtained at smaller temperatures. The simulated results show that even for very low temperature differences, the transient period in natural convection along a flal vertical plate is smaller than 3s.     

Core-shell CdS/Cd(OH)2 quantum dots: synthesis and bioconjugation to target red cells antigens

We report a new and efficient methodology of labelling red blood cells, in order to investigate the expression of anti-A antigen, employing luminescent semiconductor nanocrystals. Highly luminescent and stable core-shell cadmium sulphide/cadmium hydroxide [CdS/CdS(OH)₂] colloidal particles were obtained in the nanometre size range. The surface of these particles was characterized by using a monoclonal anti-A antibody via a one-step glutaraldehyde cross-linking procedure, followed by conjugation of the particles to red cells of blood groups A⁺, and O⁺. Laser scanning confocal microscopy images indicated that after conjugation for 30 min, A⁺ and erythrocytes presented different patterns of dual bright emission whereas the O⁺ group cells showed no emission. We suggest that this labelling procedure may be applied as a quantitative tool to investigate the distribution and expression of alloantigen in red blood cells.     

IMMUNODIFFUSION METHOD FOR DETECTION OF CLOSTRIDIUM BOTULINUM TYPES, A, B, E, AND F

Factors affecting the immuno-gel diffusion method for detecting toxigenic (tox⁺) C. botulinum type A and nontoxigenic (tax^-) C. sporogenes were studied. This procedure was extended to detect types B, E, and F using homologous and poly A-F antitoxins for proper tox^- types. Increasing glucose levels from 0 to 3% in the growth medium caused larger and more intense precipitin zones around colonies of C. botulinum type A. Precipitin zones were detected in TPGYA that contained no glucose, but better zones occurred at 4% and thereafter up to 7% glucose at pH 7.6. The most favorable titers of C. botulinum antitoxins incorporated either in gel-diffusion agar (GDA) or in growth medium varied with the C. botulinum type. The method differentiates between C. botulinum types A, B, E, F and C. sporogenes.