Stay cool and protect your analytes: Maceration vs. continuous cold extraction on a rotavapor

In this post, I shall compare two methods for performing extractions on heat-sensitive samples. The effect of heat on an analyte can be detrimental. Performing an extraction from heat-sensitive analytes requires the use of specific techniques that can separate the desired compounds without harming or destroying them. The age-old process of maceration will be compared to continuous cold extraction on a modern rotary evaporator. Which method will come out on top? Read on to find out.

It has been a particularly cold winter this year, and to stay warm, I have been cooking a lot of stews, broths, and other hearty meals. The only problem with such food is that it often requires a long time to let all the ingredients break down and blend into a delicious meal. One way to speed up the process is by using a pressure cooker. The increased pressure raises the boiling point, and you can cook at higher temperatures. The increase in temperature can, however, have detrimental effects on the ingredients, as I found out the other day while preparing a lamb stew for my family. I decided to add some mint leaves to the stew I was cooking in the pressure cooker. One problem I find using the pressure cooker is that I cannot see what is happening inside the pot. When I finally looked into the pressure cooker, I noticed that all the mint had turned black. The stew had also developed a slightly acrid taste. The problem was that the chlorophyll in the mint leaves was sensitive to high temperatures. The breakdown of chlorophyll produces a compound called pheophytin, which is responsible for the leaves’ black color. The high temperatures can also cause the breakdown of other compounds in the mint, such as essential oils, which are responsible for the mint’s characteristic flavor. The detrimental effect of heat is something chemists are keenly aware of, which has led to the development of several methods for working with heat-sensitive analytes. Today I shall describe and assess two processes chemists use to extract compounds without destroying or harming them: maceration and continuous cold extraction.

Maceration has been used for centuries as a method of extracting compounds. The basic principle is that a solid material is soaked in a liquid to release its soluble components. The process generally involves the preparation of the sample by drying it and grinding it to increase the surface area between the sample and the liquid solvent. The sample should not be too big, or the solvent will not be able to penetrate the innermost cells. The sample should also not be ground too small as this could result in the loss of volatile active ingredients. Next, a solvent, known as a menstruum, is added, and the mixture is left – often inside an airtight container – for a variable length of time, based on the sample and solvent used. The type of solvent used depends on the chemical nature of the compounds contained within the sample. Generally, ethanol is used as the solvent as it can extract a variety of molecules, including those that are both hydrophilic and lipophilic. Certain oils can be used to isolate only lipophilic components, while water can be used to extract only hydrophilic compounds. To facilitate the maceration process and increase the extraction yield, you should agitate the mixture to promote the diffusion and remove the concentrated solution from the sample surface. The maceration process usually occurs at room temperature, and the extraction often takes days.

An alternative process is to separate the desired components of a mixture by continuous cold extraction using a rotavapor. The rotary evaporator uses a rotating flask that is under vacuum and submerged in a heated water bath. The rotation creates a thin film of the mixture that gets evaporated by heat. The vacuum has the opposite effect of my pressure cooker. Rather than increasing the boiling point due to increased pressure, the boiling point is reduced due to the vacuum. This allows the evaporation of the solvent at lower temperatures. Modern rotary evaporators can perform even more complex applications, such as continuous extractions. The vaporized solvent is condensed and collected in a separate container in a continuous extraction process. The condensed solvent is then reused for the next extraction cycle. This method allows for an efficient and continuous process, as the solvent can be reused multiple times. The low temperatures prevent the degradation of heat-sensitive compounds.

To show the differences between the two methods, I shall present the results of the extraction of curcumin, the natural and bioactive compound of turmeric. The sample for both extractions was prepared by drying the sample for 18-24 hours at a relatively low heat (50-60 °C) to protect any heat-sensitive compounds. The sample was then crushed into smaller pieces using a blender. For the first extraction, the maceration method was used. 250 g of sample was placed in a glass jar with 4 L of ethanol. The maceration process occurred over 216 hours at ambient temperature before being filtered with a muslin cloth. The filtrate was then concentrated with a rotavapor to evaporate the remaining solvent, leaving the resulting extract to be measured. The same sample-to-solvent ratio was used for the continuous cold extraction, but the process was conducted over 24 hours. The results of this test revealed that the extraction process using the rotavapor produced a yield of 31.4 %, slightly more than the 28.7 % yield of the maceration process. The big difference, however, was the amount of time taken. The rotavapor was able to extract more in less time, with significantly less effort. Once set up, the process was fully automated, whereas the maceration process required continual intervention to achieve comparable results.

Compared to maceration, there are several benefits of using a rotavapor for extraction. Benefits include:

  • Efficiency: the rotavapor allows for a faster, continuous extraction where the solvent can be reused multiple times.
  • Purer extracts: the rotavapor completely separates desired compounds from the solid material, unlike maceration, where the solid materials remain in the extract and require an additional filtration step.
  • Temperature control: the rotavapor allows for precise temperature control, unlike maceration, which is subject to ambient temperatures.
  • Scale: It is easier to scale up your extraction process on a rotavapor.
  • Solvent recovery: the rotavapor allows for the recovery and reuse of the solvent, reducing costs and the process’s environmental impact.

Overall, the rotavapor offers a more controlled, efficient, and cost-effective extraction process compared to maceration. To learn more about the various types of rotary evaporators and their uses, check out my previous blog post on the subject .

Till next time,

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