I'm drying fresh soybean samples that weight about 1.5 g using a lyophilizer for the first time. I kept it in the equipment for 46 hours at -30 F, but the tissue doesn't look dry enough as stems are still flexible. How long should I keep the plant samples to achieve complete dryness?
Dear Maria,
You ask a challenging question, there are many factors which affect the drying time of plant tissue. The following are factors to consider:
Moisture content of the tissue
Size of the tissue sections
Whether the tissue is whole (e.g. whole leave or seed) or chopped
Nature of the tissue with regards water retention (seeds or desert plants are good as this, as are tissues with high sugar content such as fruits).
Drying time is a multifactorial of these issues, and how you set the equipment.
The typical process is:
Freeze the tissue
Put under high vacuum in the lyophilizer ( this should keep it frozen)
Heat the tissue in the lyophilizer to speed the drying process. If you add no heat, the time taken is much longer.
A general guide to freeze drying can be found here:
https://www.spscientific.com/freeze-drying-lyophilization-basics/
I realize that I have not answered your question with a number, I can't, but I hope that this gives you a guide. Effectively you know when things are dry because you get to a steady weight over time, however continually opening the system is not a good idea either. I would guess that drying time is likely measured in days, not hours. It could be > than a week depending on your samples. Leaf discs (created using a hole punch for paper) typically are 12 to 24 hours, at least that's what we see at the crop breaders.
Kind regards
Rob
Thanks for the information. I will read more into this subject.
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