To freeze dry plant samples, you essentially freeze them rapidly and then remove the water content through sublimation under vacuum. Here's a breakdown of the process:
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Pre-freezing: Place the plant leaves at -80°C for approximately 2-4 hours. This ensures they are completely frozen before the freeze-drying process begins. Rapid freezing is crucial to minimize ice crystal formation, which can damage the plant tissue structure.
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Loading the Lyophilizer: Arrange the frozen leaves in a single layer on the trays of a lyophilizer (freeze dryer). Avoid overcrowding to ensure efficient sublimation.
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Freeze Drying: The lyophilizer lowers the pressure in the chamber, creating a vacuum. It then gently heats the samples. The ice directly sublimates into water vapor, bypassing the liquid phase. This process typically takes several hours to several days, depending on the sample type and the lyophilizer's capabilities.
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Secondary Drying (Optional): After the primary drying phase, a secondary drying phase can be performed at a slightly higher temperature to remove any residual unfrozen water molecules.
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Storage: Once the freeze-drying process is complete, store the dried plant material in airtight containers with desiccant to prevent moisture reabsorption.
