Comparatively Speaking: Solubility vs. Extraction

Apr 24, 2012 | Contact Author | By: Anthony J. O'Lenick Jr., Siltech LLC
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Title: Comparatively Speaking: Solubility vs. Extraction
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In this installment of "Comparatively Speaking," industry expert Tony O'Lenick describes the difference between solubility and extraction, and how various extraction techniques can be used to isolate desired cosmetic actives.

Solubility

As explained in a prior column, solubility is a term that relates to the ability of a material to dissolve in a given solvent. Solubility is never complete and results in the ability to partition materials into hydrophilic and hydrophobic systems. A simple example of separation by differences in solubility is shown by placing a mixture of salt and sand in water. The salt is dissolved and the sand remains behind.

Extraction

Extraction is a process that makes use of the fact that certain materials present in a substrate can be selectively dissolved into a particular solution. On major area currently employing this technique is naturals and botanicals, to obtain actives from plants. Extraction is a well-known technique for separating chemical constituents. It is a process by which a solute is extracted from a first solvent into a second solvent, where the two solvents are immiscible. One common extraction methodology used in organic chemistry involves combining, in a separatory funnel, water and diethyl ether.

Over the centuries, a variety of techniques have been employed to extract active ingredients from botanicals. Solvent-based extraction is one such methodology. After segregating the plant material into its constituent parts, e.g., leaves, stems, fruits, branches and roots, the part with the desired active(s) is chosen, macerated (or similarly processed) and placed into the solvent. Materials that are soluble in the solvent are dissolved, leaving insoluble materials behind.

Solvent-based extraction systems are recognized as having at least two important limitations. First, they are able to extract only active materials that are soluble in the chosen solvent. Second, because many solvents lack selectivity, compounds other than those that are desired are extracted. Not only can this dilute the purity of the desired active compound, it can also negatively impact the performance benefits of the extract.

A number of techniques have been used for extracting water-soluble actives. For example, hot water extraction removes water-soluble materials, leaving behind oil-soluble materials as well as materials that are insoluble in either water or oil. Tinctures, produced using hydro-alcoholic solutions, are another extraction vehicle well-known to skilled artisans. The inclusion of alcohol alters the polarity of water, producing different and marginally more efficient (e.g., higher-yielding) extracts than water or alcohol alone. Propylene glycol is yet another commonly used vehicle to extract water- and alcohol-soluble materials.

The solvent used to extract actives is referred to as menstruum. The menstruum is chosen so that the maximum concentration of active is removed from the matrix while also minimizing the undesired materials extracted. This optimization of extraction is key to the extraction business. New silicone based menstrua have been applied to the extraction process providing some improved performance.1

Silicone Polymer Extractions

US Patent 20110201836 describes a new type of extraction based on silicone polymers having different solubilities, which allows for the customization of a menstruum to extract not only more active ingredient, but also narrower ranges of materials than has heretofore been possible. Different silicone polymers can be used to alter the ratio of silicone-soluble to oil-soluble to water-soluble to fluoro-soluble portions in the molecule; and in so doing, creating a series of polymeric materials of differing partition coefficients. Thus, many different fractions can be extracted from the same starting plant material.

The resulting extracts each can then be evaluated for their effects on reducing the signs of biological and/or or photo-aging, e.g., appearance of fine lines and wrinkles, as well as analgesic, anti-inflammatory, free radical scavenging, anti-microbial and other desired benefits. Based on a "range-finding" series of silicone polymer extraction vehicles, further refinements can be made to the polymers to maximize the concentration of and/or further isolate compounds of interest. Indeed, many compounds extracted using this process may have previously been unavailable.

Yet another advantage of this process is in terms of environmental stewardship; because extraction of the desired actives is more efficient, smaller quantities of plant materials are required to be harvested.

References
1. US Patent application 2011-0201836