Freezing and freeze-drying highly concentrated carbohydrate systems

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Wang, Rui (2017). Freezing and freeze-drying highly concentrated carbohydrate systems. University of Birmingham. Ph.D.

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Abstract

Freeze drying is a widely-used dehydration technique in food and pharmaceutical industry, involves water crystallisation (freezing) and ice sublimation during the process. The purpose of the study is to enable the initial concentration of solutions that are used in freezing and freeze drying processes to be increased, as an approach to reduce the energy consumption of the process.

Spontaneous crystallisation from both sucrose solutions and coffee solutions was studied by DSC, XRD and cryo-SEM, and results showed that increasing solid concentration (up to 70%) significantly delayed the water crystallisation, shown as lower crystallisation temperature and less or even no ice crystal formation.
A method was developed to induce water crystallisation by adding already formed ice seeds to water, which allowed the study of ice crystal growth rate at controllable conditions. The method combined the use of a temperature controlled stage and an optical microscope, and the effects of solid concentration (up to 60%), temperature, viscosity, solute type, and air bubbles on crystal growth were investigated.

Freeze drying high concentration sucrose (up to 60%) showed significant volume expansion (collapse), and methods to reduce the collapse were tried by modifying the formulation (adding high molecular weight gum Arabic) or freeze drying cycles (reducing heating rate between primary and secondary drying). Results showed that the up to 30% concentration of sucrose solution can be dried without volume expansion with modified freeze drying process.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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