Vacuum Freeze Drying Method

Study Notes

Freeze Drying

Freeze drying involves placing frozen material in an evacuated apparatus with a cold surface maintained at -60 to 80 °C.
Water vapor from the frozen material passes rapidly to the cold surface.
This method requires a relatively complicated apparatus and is more expensive than hot-air drying.
It is not commonly used, except for heat-sensitive substances.

Preservation of Plant Materials

Enzymatic reactions will slowly destroy the constituents of plant materials during long storage.
Stabilization is a process to destroy enzymes, and in aloe, this process eliminates bacteria and anthraquinones (laxatives) via a super chilled ethanol bath.

Fermentation

Fermentation involves placing fresh material in thick layers, sometimes covered and often exposed to raised temperatures (30-40 °C) and humidity.
This treatment accelerates enzymatic processes, and the fermented product must be dried afterwards to prevent attack by bacteria and fungi.

Extraction and Fractionation

Soxhlet Apparatus

The powdered material is continuously extracted with suitable solvents in a Soxhlet apparatus.
This method is not suitable for heat-sensitive materials.

Counter-Current Extraction

In counter-current extraction, wet raw material is pulverized and mixed with extraction solvent.
The starting material moves in one direction within a cylindrical extractor, and the extract becomes more concentrated as it moves.
Complete extraction is possible when the quantities of solvent and material and their flow rates are optimized.

Ultrasound Extraction (Sonication)

Ultrasound is propagated in the extracted liquid, resulting in cavitation bubbles in a solvent material.
The acoustic characteristics transmitted to the related material are in the frequency range of KHz ~ MHz.

Blast Sifting

Blast sifting involves blowing the material to be classified with compressed air into an apparatus.
Coarse, heavy particles settle fast, while small, light particles stay in the air stream for a longer time.

Storage and Packing of Crude Drugs

Drugs containing glycosides and esters are less stable than those containing alkaloids.
Storage conditions should be dry, with careful exclusion of light and protection against insect attack.
Tannins have an almost unlimited durability, while drugs with essential oils deteriorate quickly through evaporation, oxidation, and polymerization.

Description

This quiz covers the vacuum freeze drying method, involving placing frozen material in an evacuated apparatus with a cold surface to remove water vapor. The method is complex, expensive, and used for heat-sensitive substances only.