Effect of lyophilization on the structure and phase changes of PEGylated-bovine serum albumin

Poly (ethylene glycol) (PEG) conjugation masks the protein's surface and increases the molecular size of the polypeptide, thus preventing the approach of antibodies or antigen processing cells and reducing the degradation by proteolytic enzymes. Proteins are readily denatured by numerous stresses arising in solution (e.g., heating, agitation, freezing and pH changes) or by chemical reactions (e.g., hydrolysis and deamidation), many of which are mediated by water. Lyophilization is most commonly used to prepare dehydrated proteins, which, theoretically, should have the desired long-term stability at ambient temperatures. Through Raman spectroscopy, differential scanning calorimetry (DSC) associated with the determination of water content by Karl Fisher titration, it was observed that after the modification of BSA–PEG in a ratio of 1:0.25 showed lower degree of structural alterations and consequently lower variation on the physical–chemical characteristics when it was compared to BSA–PEG (1:0.5). Moreover, the BSA–PEG (1:0.25) optimizes the conditions during the lyophilization process and storage of the protein.