Ultrasound freeze-drying

The ultrasound-assisted extraction of freeze-dried plant-based materials normally takes 2 hr. If the extract is evaporated to dryness, a total of 3 hr is necessary. As an additional sample preparation step, 2 to 4 days should be allotted for freeze-drying fresh plant materials, depending on the quantity of the material. Homogenizer-assisted extraction of fresh fruit takes <4 hr. 

Five grams of starch-g-polyacrylamide was dispersed in 333 ml of water and the mixture was heated for 4.5 hr at 95-100°C. The cooled dispersion was then treated with ultrasound, as described for starch-g-PAN in DMSO. The resulting solution was gravity-filtered through fluted Whatman 54 paper, and the filtrate was freeze-dried to give 4.4 g of polymer. To give a denser, more compact product, which might more closely resemble soluble starch-g-PAN, the freeze-dried polymer was dispersed in 20 ml of water, and the polymer was precipitated from the thick paste by addition of ethanol. The polymer was separated by filtration, washed with ethanol, and vacuum dried at 60°C. 

The first chapter introduces both general aspects of sample preparation and the main problems encountered in automating sample treatments. The second provides a brief discussion of the underexploited potential of freeze-drying for delivering samples in forms that facilitate their subsequent analysis. Chapter 3 is devoted to a kind of energy that has also received inadequate attention from analysts ultrasounds. 

Ultrasound-Responsive Liposomal Preparation by Freeze-Drying Method... 

Hottot, A., Nakagawa, K., Andrieu, J., 2008. Effect of ultrasound-controlled nucleation on structural and morphological properties of freeze-dried manitol solution. Chem. Eng. Res. Des. 86 193-200. 

Andrieu, J., 2006. Influence of controlled nucleation by ultrasounds on ice morphology of frozen formulations for pharmaceutical proteins freeze-drying. Chem. Eng. Process. 45 783-791. 

A more detailed treatment of the application of ultrasound is provided in Chapter 8, along with a discussion of the principles of generation and transmission of ultrasound energy to the material to be treated. It is pointed out that power ultrasound can be used to assist both, liquid-solid processes, such as brine treatment, and drying. The acoustic field is shown to enhance, by a number of mechanisms, both, the external and the internal mass transfer when combined with hot air or atmospheric freeze drying of vegetables and fruits. The more porous the material, and the lower the permissible temperature and gas velocity, the higher is the intensification that can be reached by application of power ultrasound. 

In this chapter, relevant background information will be provided regarding the principles of PEF and ultrasound technology, and its impact on biological tissues. The application of PEF as a pretreatment of raw materials prior to osmotic dehydration, air- and freeze-drying, with the resultant effects on drying characteristics and product quality, will be discussed. In the case of ultrasound, concepts for... 

Ultrasonic waves can be excited into screens, which transfer the vibration to the food product, and the ultrasound emitter can be attached to the center of the screen, as well as to its frame. Direct transmission to the product allows sonication to be used in a large variety of food processes, throughout the complete drying process. Future equipment developments could enable ultrasound-mediated transfer not only to screens but also to trays or conveyor belts, and in this way airdrying in batch systems, as well as in continuous systems, could be assisted by ultrasonic vibrations. Even in vacuum freeze-drying, where air transmission is impossible due to the vacuum, the product can be placed on supports and treated with ultrasonic waves (Schbssler et al, 2012b). 

---