A glass transition temperature approach for the prediction of the surface stickiness of a drying droplet during spray drying

The development of surface stickiness of droplets of sugar and acid-rich foods during spray drying can be explained using the notion of glass transition temperature (T-g). In this work, criteria for a safe drying regime have been developed and their physical basis provided. A dimensionless time (psi) is introduced as an indicator of spray dryability and it is correlated with the recovery of powders in practical spray drying. Droplets with initial diameters of 120 mum were subjected to simulated spray drying conditions and their safe drying regime and 41 values generated. The model predicted the recovery in a pilot scale spray dryer reasonably well. (C) 2004 Elsevier B.V. All rights reserved.

Simulation of the cake formation and growth in cake filtration

A computer model was developed to simulate the cake formation and growth in cake filtration at an individual particle level. The model was shown to be able to generate structural information and quantify the cake thickness, average cake solidosity, filtrate volume, filtrate flowrate for constant pressure filtration or pressure drop across the filter unit for constant rate filtration as a function of filtration time. The effects of particle size distribution and key operational variables such as initial filtration flowrate, maximum pressure drop and initial solidosity were examined based on the simulated results. They are qualitatively comparable to those observed in physical experiments. The need for further development in simulation was also discussed. (c) 2006 Elsevier Ltd. All rights reserved.

Applications of the cyclone stickiness test for characterization of stickiness in food powders

The cyclone stickiness test (CST) technique was applied to measure the stickiness temperature and relative humidity of whey, honey, and apple juice powders. A moisture sorption isotherm study was conducted to analyze the surface moisture content of whey powder. The glass transition temperatures of the sample powder were analyzed using differential scanning calorimetry (DSC). The stickiness results of these products were found within 20 degrees C above their surface glass transition temperatures, which is well within the normal temperature range for glass transition in general. The results obtained by the CST technique were found consistent with DSC values.

Applications of Thermal Mechanical Compression Tests in food powder analysis

A new Thermal Mechanical Compression Test (TMCT) was applied for glass-rubber transition and melting analyses of food powders and crystals. The TMCT technique measures the phase change of a material based on mechanical changes during the transition. Whey, honey, and apple juice powders were analyzed for their glass-rubber transition temperatures. Sucrose and glucose monohydrate crystals were analyzed for their melting temperatures. The results were compared to the values obtained by conventional DSC and TMA techniques. The new TMCT technique provided the results that were very close to the conventional techniques. This technique can be an alternative to analyze glass-rubber transition of food, pharmaceutical, and chemical dry products.

Thin-layer isothermal drying of fructose, maltodextrin, and their mixture solutions

Solutions of fructose, maltodextrin (DE 5), and their mixtures at the ratios of 20:80, 40:60, 50:50, 60:40, and 80:20 were gelled with 1% agar-agar and dried under convective-conductive drying conditions. The thin slabs were maintained at isothermal drying condition of 30 and 50 degrees C. Yamamoto's simplified method based on regular regime approach was used to calculate the (effective) moisture diffusivity. Both the drying rates and the moisture diffusivity exhibited strong concentration dependence. The concentration dependence was stronger in the case of fructose and fructose rich solutions. Both the moisture diffusivity and drying rates of the mixture solutions were enhanced due to plasticization of fructose on maltodextrin, which is explained through free volume theory.