Surface composition of industrial spray-dried milk powders. 2. Effects of spray drying conditions on the surface composition.

Spray drying is a mild and cost-effective convective drying method. It can be applied to stabilise heat sensitive ingredients, such as enzymes and probiotic bacteria, albeit in industrial practice for example freeze drying or freezing are often preferred. The reason is that optimum drying conditions and tailored matrix formulations are required to avoid severe heat damage leading to loss in enzyme activity or reduced survival of bacteria. An overview is provided on the use of protective carbohydrate-rich formulations in the spray drying of enzymes and probiotics. Subsequently, single droplet drying experimentation methods are reviewed for mapping drying trajectories of individual droplets. The advantage of these is to provide insight in inactivation kinetics of enzymes and probiotics and thus contribute to unravelling of stabilisation mechanisms. Finally, it is shown that detailed modelling of single droplet drying and insight in micro-structural changes during drying can be complementary to the experimental single droplet approaches.

Single droplet drying for optimal spray drying of enzymes and probiotics

The objective of this study was to determine a mathematical model for the reaction kinetics of ascorbic acid degradation to describe the rate of vitamin C loss in a drying process of tomato halves or tomato pulp. Tomato samples with different moisture contents were heated at specified temperatures for different time periods. The kinetics of ascorbic acid degradation followed a first-order reaction with a reaction rate constant dependent on product moisture content, in addition to temperature. Furthermore, there was a maximum rate constant when the moisture content of tomato samples was between 65 and 70%. These effects were expressed by a linear relationship between temperature, moisture content, and natural logarithm of rate constant. The model was used to simulate the vitamin C loss during drying of tomato halves and two drying processes of tomato pulp—evaporative concentration and spray drying. It was concluded that there was a close agreement between the experimental and predicted values of ascorbic a...

Retention of Ascorbic Acid during Drying of Tomato Halves and Tomato Pulp

Retention of ascorbic acid during drying of tomato halves and tomato pulp

The study is an extension of an optimization study, which was planned to determine the optimum spray drying conditions (the feed, outlet and inlet air temperatures) for producing yoghurt powder. The resulting yoghurt powder at each condition was subjected to the measurement of physical properties, moisture content, and reconstitution properties. All the reconstitution properties of yoghurt powders produced under 20 different spray drying conditions according to CCRD experimental design were affected by the drying outlet temperature only. Furthermore, the bulk (bulk and tapped densities, porosity, flowability, hygroscopicity and degree of caking) and particle properties (particle size distribution, particle density and morphology) of yoghurt powder obtained from optimum spray drying conditions were also determined. The bulk, tapped and particle densities of yoghurt powder were 538, 746 and 1177 kg/m3, respectively. The mean diameter (D4.3) and the span value of yoghurt powder were 3.053 and 2.487 μm, respectively.

Physical properties of yoghurt powder produced by spray drying

This work aims at identifying the effects of the main operational spray-dryer variables on the milk powder quality. Experiments have been performed in a pilot spray-dryer following the full-factorial design technique to provide data and correlations that predict the whole powder properties as function of the main operational variables of the spray-dryer. The emulsion feed flow rate, the atomization rotation and the inlet air temperature have been chosen as the independent variables while the residual moisture content, the tapped bulk density, the cohesion force enhancement between particles as well as size distribution of agglomerate and its morphology are the response variables that quantify the powder quality. Correlations obtained are analyzed and incorporated into a mathematical model previously developed for simulating the spray-drying of whole milk emulsion.

Effect of Spray-Dryer Operating Variables on the Whole Milk Powder Quality

In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves.

Characterization of the Residence Time Distribution in Spray Dryers

Inorganic particulates are usually dried in a fixed bed, fluidized bed, or spray dryers. These compounds are easy to dry, once their physical structure, with high porosity, allows moisture content removal with low resistances. For fluidized bed of alumina particle evaluations, a laboratory-scale drying unit was built. The drying experiments were carried out with alumina particles with different diameters to evaluate temperature and air flow rate effects on drying kinetics and bed height. In another case, the dehydration of a mixture of rare-earth chlorides in a fluidized bed was studied, aiming at the production of anhydrous rare-earth chlorides, used to obtain mischmetal by electrolytic and metallothermic processes. The spray drying experiments were carried out in a pilot plant. Spray drying is a technique largely applied in industrial processes to dry solutions or suspensions, converting their solid parts into a dried powder. A set of rare-earth drying experiments was carried out, aiming at the...

Drying of Inorganic Particulate Compounds

This work aims at identifying the effects of the main operational spray dryer variables on the milk powder. Experiments have been performed in a pilot spray dryer following the full-factorial design technique to provide data and correlations that predict the powder properties as function of the main operational variables of the spray dryer. The emulsion feed flow rate, the atomization rotation and the inlet air temperature are chosen as the independent variables and the response variables that quantify the powder quality are: residual moisture content, tapped bulk density, cohesion force enhancement between particles as well as size distribution of agglomerate and its morphology. Correlations obtained are analyzed and incorporated into a mathematical model previously developed for simulating the spray drying of milk emulsion.

The influence of spray dryer operation variables on milk powder quality

No presente trabalho e apresentado um estudo do tempo de residencia de particulas em um “spray dryer” com contato ar/spray predominantemente co-corrente e sistema rotativo de atomizacao de amostra. Propoe-se a aplicacao de uma tecnica nuclear, utilizando como tracador o radioisotopo La140. A metodologia baseia-se na injecao do tracador na corrente de alimentacao e o monitoramento da sua concentracao na saida do equipamento. As experiencias sao realizadas durante a secagem de suspensoes de oxido de gadolinio. As funcoes de distribuicao de tempos de residencia obtidas experimentalmente apresentaram comportamento esperado e boa reprodutibilidade, indicando que a tecnica aplicada e perfeitamente adequada a esse tipo de equipamento.

http://carpedien.ien.gov.br:8080/bitstream/ien/1784/1/Estudo%20Experimental%20do%20Tempo%20de%20Resid%c3%aancia%20de%20Particulas%20em%20Secador.PDF

Gloria Regina da Silva Wildhagen

Papers

Effect of Spray-Dryer Operating Variables on the Whole Milk Powder Quality

Characterization of the Residence Time Distribution in Spray Dryers

Drying of Inorganic Particulate Compounds

The influence of spray dryer operation variables on milk powder quality

Estudo experimental do tempo de residência de partículas em secador "spray"