Effects of freezing and the cryoprotectant lactobionic acid in the structure of GlnK protein evaluated by circular dichroism (CD) and isothermal titration calorimetry (ITC).

Freezing is a widely applied method in food preservation. The technique has negative effects on sensory and textural properties of some foods. In this study the effects of the freeze-thaw process and lactobionic acid (LBA) as a cryoprotectant on GlnK protein solution were evaluated by circular dichroism (CD) analysis and isothermal titration calorimetry (ITC). The freeze-thaw cycles caused changes in GlnK conformation and interactions with small ligands (adenosine triphosphate, ATP). CD assay demonstrated changes in the molar ellipticity values of the samples subjected to freezing, indicating conformational changes to the GlnK protein. Additionally, ITC analysis indicated that the freeze-thaw process caused changes in the interaction properties of GlnK with its ligand ATP. LBA cryoprotectant activity was also evaluated and with both of the techniques it was demonstrated that the compound prevented the damage caused by the freeze-thaw process, thereby maintaining the characteristics of the samples.