What Does Lyophilized Mean? Freeze-Dried Peptides Explained

Lyophilized means freeze-dried. A lyophilized peptide has had its water removed under vacuum at low temperature, which leaves a dry powder or "cake" in the vial. Research peptides are supplied this way because a dry peptide is far more stable than one in solution.

How lyophilization works

Freeze drying runs in three stages (GEA):

1. Freezing. The solution is frozen at atmospheric pressure. How fast it freezes affects the size of the ice crystals, which affects how quickly water can leave later.
2. Primary drying. Under vacuum, the ice is removed by sublimation, turning straight from solid to vapor without melting. This stage ends once all the ice is gone.
3. Secondary drying. Water still bound to the material is removed by desorption. This step is tightly controlled so the product isn't over-dried.

After drying, vials are usually closed under vacuum or under a dry inert gas such as nitrogen. Freeze-dried products are often very hygroscopic, meaning they readily absorb moisture from the air (GEA).

Why freeze-dried peptides are more stable

Several of the reactions that degrade peptides, such as hydrolysis and deamidation, need water. Removing it lets a peptide be stored much longer. Peptide manufacturers recommend keeping lyophilized peptides sealed and frozen for long-term storage, and they advise against long-term storage in solution (Bachem).

What lyophilized powder looks like

A lyophilized peptide usually appears as a white or off-white powder or a solid cake at the bottom of the vial. The amount can look very small. A few milligrams of freeze-dried material takes up little volume, and the cake may break up or stick to the vial walls during shipping. That's normal and doesn't change the amount in the vial.

How long lyophilized peptides last

Shelf life depends on the sequence and on storage. Peptides containing cysteine, methionine, tryptophan, asparagine or glutamine are less stable (Bachem). Moisture greatly reduces long-term stability (Sigma-Aldrich). Sealed, dry and frozen is the condition that gives the longest life. Lyophilized peptides are commonly shipped at room temperature, and Bachem notes that 4 °C is acceptable for short-term storage.

For full storage guidance, see How to Store Lyophilized Peptides. To check a vial's lot against its test results, see the Certificates of Analysis page.