Efficiency and safety are two issues of central importance when it comes to extracting bio-compounds for food and medicinal purposes. Additionally, extraction methods that are friendly to the environment are just as important as those that are safe and effective which is why mechanochemical-assisted extraction (MCAE) is a desirable way to extract bio-compounds for food and medicine. 
MCAE is a relatively new form of extraction. It was first employed in 2003 when Korolev et al  used it to extract triterpenic acids. Because the technique uses very little or no organic solvent, it has garnered much attention since its first reported use.
MCAE essentially consists of three steps: source material preparation, mechanochemical treatment of the prepared source material, and extraction.  During the preparation stage, the raw material is completely dried and then pulverized into fine particles optimally measuring between 0.5-2 mm.  According to Zhu et al , finer particle sizes are desirable when extracting flavonoids and terpene trilactones from the leaves of the ginkgo plant.
Afterwards, the material is placed in a ball mill and mixed with one of many different reagents. These include sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), sodium hydroxide (NaOH), silicon dioxide, (SiO2), or hydroxypropyl-β-cyclodextrin (HP-β-CD), to name a few. [1,4] The choice of reagent depends heavily on the source material to be used.  For example, Xie et al  demonstrated that NaHCO3 was not as effective as Na2CO3 in pulling flavonoids from bamboo leaves.
The purpose of this second step is to change the chemical nature of the compounds found in the source material to make them more water soluble.  Doing so allows the use of water for extraction instead of or alongside of a small amount of chemical solvent, which makes the process of extraction cheaper and safer. After the solution (which is now in salt form due to the reagent) is dissolved in water, it must be returned to its original form. This is accomplished through acidification. 
Because it is a relatively new and alternative technique, MCAE needs more study. However, what is known is that its use of water as a solvent and relatively short extraction time make it a very attractive method of extraction. Also, MCAE does not require high temperatures, which are known to degrade or even destroy source materials and their desirable compounds. 
Image Source: Karolina Grabowska, Pexels
- Wu K, et al. Mechanochemical assisted extraction: A novel, efficient, eco-friendly technology. Trends in Food Science and Technology. 2017;66:166-175. [Impact Factor: 11.077; Times Cited: 8 (Semantic Scholar)]
- Korolev KG, et al. Mechanochemical preparation of water-soluble forms of triterpene acids. Chemistry of Natural Compounds. 2003;39(4):366–372. [Impact Factor: 653; Times Cited: 30 (Semantic Scholar)]
- Zhu X-Y, et al. Response surface optimization of mechanochemical-assisted extraction of flavonoids and terpene trilactones from Ginkgo leaves. Industrial Crops and Products. 2011;34(1):1041–1052. [Impact Factor: 4.244; Times Cited: 25 (Semantic Scholar)]
- Xie J, et al. Mechanochemical-assisted extraction of flavonoids from bamboo (Phyllostachys edulis) leaves. Industrial Crops and Products. 2013;43:276–282. [Impact Factor: 4.244; Times Cited: 33 (Semantic Scholar)]