I tried the liquid nitrogen prior to freeze drying it help to reduce the drying time however quality of powder may be little bit different from only freeze dried.

Hi

I have used freeze dryer for the preparation of protein hydrolysate powder...The sample was kept at 80C freezer overnight prior to lyophilization/freezedrying...In spite of this, using liquid nitrogen might improve drying behavior but properties of the dried material may vary in terms of functionality and textural.

Cryogenic freezing can be used for a small sample however, it is better to maintain lower temperature before freeze drying. Rapid freezing followed by FD definitely differ the microstructure from the freezing at -60C and FD.

"Flash" freezing with LN2 creates a very very small crystalline structure in the frozen cake. This small crystalline structure, in turn, results in small pores in the freeze dried cake making it difficult for the subliming vapor to leave the product freely and easily. I also believe that depending on the thermal characteristics of the product, you could freeze in LN2 and as you introduce the product to the freeze dryer and it subsequently warms up you will see a change in the water crystals within the product. Slower freezing leads to larger ice crystals and a more porous cake. Critical factor is to have thermal analysis done so you understand the freezing and melting characteristics of your product.

In certain food freeze dryers, the freezing of the product is also accomplished by spraying liquid nitrogen in the drying chamber in which the product is placed.