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We all know that many factors can affect the stability of active components in the freeze-drying and storage process of food, medicine, and biological organisms, and even lead to inactivation. Most drugs and biological products require the addition of suitable freeze-drying protectants and additives to be prepared into a mixture before effective freeze-drying and storage can be carried out. And sucrose is one of the commonly used freeze-drying protectants.
First of all, before discussing the advantages of sucrose for sale as a freeze-drying protectant, we first need to explain why it can be used as a freeze-drying protectant for biological products.
To protect the quality and activity of active substances such as proteins in biological products, we usually add sugar protectants to the drug formula for freeze-drying. There are currently two main hypotheses for the freeze-drying protection mechanism——the glassy state hypothesis and the water replacement hypothesis.
The viscous protectant surrounds the protein molecule, forming a carbohydrate glass structure similar in structure to glassy ice, which hinders the chain movement of large molecular substances, prevents the stretching and precipitation of proteins, and maintains the stability of the three-dimensional structure of protein molecules, thereby exerting a protective effect.
After the protein loses water during freeze-drying, the hydroxyl groups of the protectant can replace the hydroxyl groups of water on the surface of the protein to form a hypothetical hydration film on the surface of the protein, which can protect the bond positions of hydrogen bonds from being directly exposed to the surrounding environment, thus preventing protein denaturation due to freeze-drying.
The theoretical basis of these two hypotheses is to achieve partial or complete vitrification freezing of the drug solution, so suitable freeze-drying protectants need to have the following four characteristics: high glass transition temperature, low hygroscopicity, low crystallization rate, and no reducing groups.
Experimental results have shown that monosaccharides (such as glucose and galactose) cannot play a protective role in the freeze-drying process of proteins. This is because monosaccharides can only provide weak stabilizing effects during the freezing process, and protein irreversible denaturation occurs before dehydration drying.
Disaccharides are very suitable protectants, which can increase the free energy of proteins during freezing to prevent protein denaturation, and replace the hydrogen bonds between proteins and water molecules to stabilize proteins during drying and dehydration, and do not contain reducing groups, so they will not cause bioproducts to undergo protein browning reaction and deterioration inactivation.
The protective effect of sugar depends on the type of protein, so suitable protectants for drugs need to be determined by comparing experimental data. At present, sucrose and trehalose in disaccharides are the most studied and recognized effective biological product protectants.
Among them, sucrose is a non-reducing disaccharide formed by the condensation of glucose and fructose through isomeric hydroxyls. It has a high glass transition temperature and plays a significant role in inhibiting the change of protein secondary structure, extending and aggregating protein polypeptide chains during freeze-drying treatment and the storage period, and has been applied as a protectant in freeze-dried preparations of proteins and ji su drugs, as well as virus vaccines.
