In the freeze-drying and storage process of food, drugs and organisms, many factors (such as chemical composition, freezing rate, freezing and dehydration stress, glass transition temperature, residual moisture in dried solids, temperature and humidity of storage environment, etc.) will affect the stability of the active components and even lead to inactivation. A large number of experimental studies have shown that, in addition to some food, human plasma, milk and other few materials can be directly freeze-dried, most drugs and biological products need to be added with appropriate freeze-drying protective agents and additives to prepare a mixed solution before they can be effectively freeze-dried and stored.
There are currently several classification methods for protectants:
1) Classification by Relative Molecular Weight
(1) low molecular compound. It can also be divided into acidic substances, neutral substances and alkaline substances.
(2) macromolecular compounds. Mainly such as albumin, gelatin, soluble starch, dextrin, gravy, pectin, gum Arabic, hydroxymethyl cellulose, algae, etc., as well as natural mixtures such as skim milk, serum, etc.
As for the mechanism of protective agent of Lyophilization Equipment, it is generally believed that low molecular compounds play a direct role in the freeze-drying process, while high molecular compounds promote the protective effect of low molecular compounds. Therefore, when preparing the protective agent formula, low and high molecular compounds are usually used together.
2) classification according to protective agent function and nature
(1) Freeze-drying protection. Substances that can prevent denaturation of active components during freezing and drying.
(2) filler. A substance that can prevent the effective components from sublimating and escaping together with water vapor and shape the effective components.
(3) Anti-grading agent. It is used as a substance to prevent biological products from oxidative deterioration during freeze-drying and storage. Such as vitamin d, vitamin e, protein hydrolysate, sodium thiosulfate, etc.
(4) acid-base regulator. A substance that can adjust the pH of a biological product to the most stable region of an active substance during a freeze-dry bath process and a storage process.
3) Classification according to substance type
Such as sugar/polyols, polymers, surfactants, nitroacids and salts.
In the freeze-drying formula of the Freeze Dried Fruit Machine, in addition to the active components and solvents, various additives are also used. Some of these additives are called protective agents, some are called additives, and some are called excipients. However, there is no unified name so far. The word excipient comes from pharmacy. Originally, it refers to the inactive substance auxiliary materials (such as gum Arabic, box pulp, starch) that constitute the drug antigen, especially the substances added to make the mixture have higher adhesion when there is a large amount of liquid in the drug mixture so as to prepare pills or tablets. Later, the name of excipient was expanded. According to the statistics of literature, the word "excipient" is widely used in freeze-drying formula.
In the freeze-drying formula of biological products, some additives can only play a specific role, while other additives can play several roles simultaneously.