Ice Formation Mechanisms of Aqueous Sucrose Solutions

An in-situ study of the influence of concentration and cooling rates on the freezing behaviour and according structural changes of aqueous sucrose solutions.

Saccharides in aqueous solutions are well known cryoprotectant materials which may preserve living cells from freezing. This fact plays an important role for animals and plants living in cold regions as saccharides incorporated in the cells do have a major influence on their freezing tolerance.

On the other hand freezing mechanisms are essential in preparing biological tissue or in the food industry. These mechanisms are strongly affected by the pres-ence of solutes; e.g. freezing-point (Tcryst) depression and a lowering of the melting temperature (Tmelt) can be observed depending on the solute concentration as well as on the cooling rates.

So far many studies on ice formation behaviours of water and aqueous solutions were done with (electron) microscopy. X-ray diffraction (XRD) studies however are needed to distinguish the structures of the formed ice, which amongst others may be hexag-onal ice (Ih) as the stable form, cubic ice (Ic) as the metastable form or vitrified water. The structure of ice is dependent on the cooling rate. In general Ic forms smaller crystals compared to Ih. For that reason there is less structural damage in biogenic tissue in case Ic is the dominant ice form.

This report describes the possibility to study the freezing and melting processes and related structural changes with in-situ XRD of aqueous sucrose solutions.

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