Why extract when you can just consume the whole plant? Extracts concentrate the bioactive part of plants into a manageable dose, while removing the inert parts such as cellulose. And since a lot of botanicals that support health don’t taste very good, we would prefer to be able to consume them as one or two capsules—not 10 or 20.
Yet, as many tea connoisseurs know, making tea is both an art and a science. The quality of the cup of tea is predicated on a number of variables that include raw material composition, the solvent (such as water or alcohol), the amount of tea to water, the water’s temperature and steeping time. Changes in these variables necessarily results in differences in the end product that are detectable by the human palate.
Let’s say you want to make a powdered extract from this cup of tea. The temperature, time and method of removing the water all impact the quality of the end product. To standardize the extract to a certain specification, including potency, color, powder size and impurities, requires another additional set of controls and experience.
Lastly, maintaining consistency from batch to batch is an additional challenge with natural products prone to variations in climate, geography and harvest methods.
The choice of solvent is a key variable that, along with raw material selection, has the most impact on the final extract. Different solvents will extract different classes of bioactive compounds, so it is important to know what you are trying to extract.
Historically, extraction facilities often selected solvents that provided the best yield, with little regard for safety or regulatory acceptance. As regulators and consumers have become more discerning, so have the processing methods. Today, “green” extraction methods offer a lot of the positives consumers demand—but not without some key tradeoffs.
Like dissolves like, so water will dissolve similarly polar compounds such as flavonoids. Water as a solvent is often preferred by consumers because of its “clean” image; however, it is also a challenge to work with as a master oxidizing agent and a great medium for microbial growth.
Due to its low vapor pressure, water is also among the most difficult solvents to remove during drying, resulting in extra heat and time that can further degrade the native composition of the original plant. Powdered extracts made with water are often hygroscopic, meaning they attract moisture from the air readily, which can lead to clumping and microbial growth in what was once a perfectly clean and flowable extract.
Ethanol is often preferred as a solvent, because it does not present many of the challenges of water. Many generations of physicians have produced liquid extracts known as tinctures—herbs steeped typically in ethanol at established concentrations.
Ethanol is good to dissolve diverse types of compounds, but for many fat-soluble molecules, saturation is reached at a low concentration, resulting in poor extraction efficiency. Thus, extracts using ethanol only often demand a premium price, and may not reach the level of potency offered by other non-polar solvents.
Supercritical extracts using solvents such as carbon dioxide (CO2) have become popular, and for good reason. This method of extraction can be performed at moderate temperatures, and CO2 is one of the cleanest and lowest cost solvents around. Supercritical CO2 is often used to remove caffeine from tea, and extract essential oils from spices and herbs.
The main disadvantages of supercritical extraction include high capital and operating costs, poor selectivity of compounds without optimization, and the time and expertise required to perfect or optimize a process. Often, to achieve a standardized product, a supercritical extraction may have to be paired with other processing methods, which can add to cost.
Standard methods of extraction can be complemented with emerging technologies to achieve a superior product.
Ion-exchange chromatography is one of the best ways to purify natural products, although the higher concentrations of actives achieved are offset by lower yields and higher processing costs. Ultrasound and microwave-assisted extraction are newer ways to achieve better yields during standard solvent extraction, as they act to break the plant cells and release active components better than simple heat or static mixing.
Today’s botanical extraction toolbox offers endless possibilities to achieve desired purity while retaining the natural composition of the botanical.
By: Blake Ebersole
This article was first published in Natural Products Insider in February 2015