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Freezing is a very important operation in the biotechnological and biopharmaceutical industries. Biological materials, such as proteins, are insufficiently stable for distribution and storage in aqueous solutions. Therefore proteins are often frozen or freeze-dried to achieve the desired 'shelf-life'. However, the freezing and freeze-drying process can cause loss of functional properties and conformational changes of proteins and affect the quality and yield of the protein products. Care must be taken to avoid any damaging effect on the proteins and other biological agents in solution. One of the identified factors affecting protein denaturation or cell survival is the solute redistribution due to freeze concentration. However, there are few data on freeze concentration due to difficulties with performing the experiments. In this work, solute redistribution during freezing in protein solutions is investigated using a purpose-built cylindrical test cell. Sodium permanganate is used as a substitute for NaCl in some experimental work as its concentration can be easily measured using a spectrophotometer. Freezing concentration was clearly demonstrated and it was found to be dependent on the freezing rate. The freezing of LDH protein solution was also studied. The concentration redistribution of LDH, together with NaCl in solution, was experimentally determined. It is concluded that the redistribution of protein concentration during freezing is not significant and can be neglected in practical analysis. The redistribution of NaCl in LDH solution during freezing is still significant, although the non-uniformity is greatly reduced compared to just salt aqueous solution case. This is due to macromolecules hindering diffusion and possible protein binding.

Original publication




Journal article


Food and Bioproducts Processing: Transactions of the Institution of of Chemical Engineers, Part C

Publication Date





35 - 40