Spray drying is the most commonly used technique for dehydration of infant dairy products. 

A poorly conducted drying operation can lead to the non-compliance of the product as well as to substantial economic losses.  The method (SD²PÒ - INRA software for predicting spray-drying parameters) used to predict the major drying parameters does not provide information about the product's sensitivity to stickiness during drying.  Stickiness is linked to the glass transition temperature of the concentrate, which is complex and even impossible to rapidly determine for solutions that contain a large quantity of water.  Given the diversity and the complexity of infant milk formulas taken as study models, a simple and rigorous method to predict the drying behaviour of concentrates is essential.   

The aim of this research is to study the transfer of water during drying and to propose a method that would make it possible to predict the drying behaviour of infant dairy products in order to control the drying operation.  We have developed the following strategy: (i) Development of a method to estimate the dry glass transition temperature  of the concentrate in order to determine its sensitivity to stickiness, and of a method that uses the point of divergence to then optimise the drying parameters; (ii) Development of a "glass-filament" desorption method adapted to the REA approach that, combined with the SD²PÒ approach, makes it possible to have access to the characteristics of the product during drying.   

We have developed a mathematical model that takes the glass transition temperature and the points of convergence into account.

Validation tests on infant formulas carried out on the INRA pilot drying tower revealed that the deposit rate of the powder in the chamber is inversely correlated with the dry glass transition temperature  of the concentrate and that the use of drying parameters determined by the point of divergence makes it possible to reduce the deposit in the chamber.  Good coherence on the material balance was observed.

Research is currently under way to improve our prediction capability and to extend this method to other non-dairy food concentrates (soy powder, etc.) and thus generalise this approach.

Partnership

Laiterie de Montaigu, LISA http://www.lisainfantmilk.com/ Eric Blanchard, Manager  e.blanchard@laiteriedemontaigu.com

Publications

ZHU P., PATEL K., LIN S., MÉJEAN S., BLANCHARD E., CHEN XD., SCHUCK P., JEANTET R. Simulating industrial spray drying operations using a reaction engineering approach and a modified desorption method. Drying Technol. 29, 419-428 (2011).
ZHU P., MÉJEAN S., BLANCHARD B., JEANTET R., SCHUCK P. Prediction of dry mass glass transition temperature and the spray drying behaviour of a concentrate using a desorption method. J Food Eng. 105, 460-467 (2011).