Supercritical Fluid Technology:

Supercritical Fluid Technology:
A Powerful Tool for the Nutritional Industry

by Jose L. Martinez, Ph.D.

In the last decade, new trends have emerged in the food industry. Thesetrends include an enhanced concern for the quality and safety of food products,increased preference for natural products over synthetic ones, and broadenedregulations related to nutritional and toxicity levels of active ingredients.Consumers are more educated and health conscious than ever before, and aredemanding higher quality products for consumption. These trends have drivensupercritical fluid technology to become the primary alternative to traditionalsolvent extraction for the extraction and fractionation of active compounds.

Supercritical fluid extraction is an extraction process using a supercriticalfluid as a solvent. When a fluid is taken above a particular temperature andpressure (critical point of the respective fluid), it exists in a conditioncalled the supercritical fluid state. The physio-chemical properties of a fluidin the supercritical state are in between those of a typical gas and liquid. Forexample, the density of a supercritical fluid can be changed by varying thepressure on the fluid. As a result, a supercritical fluid can have a densitythat ranges between those exhibited by gases to liquid-like values when thefluid is compressed at high pressures. Carbon dioxide is certainly the mostpopular fluid because of its physiological compatibility, non-toxicity,inflammability, easy availability, convenient critical parameters (Tc= 31degrees Celsius, Pc= 7.38 MPa), inexpensiveness and environmental friendliness.

Supercritical fluid processing shows numerous advantages when compared totraditional organic solvent extraction. In traditional extraction, for example,the residual solvent is unavoidable and is usually measured in parts per million(ppm). In supercritical fluid extraction, however, there is no residual solventin the final product. This translates into lower operating costs because of thereduction in post-processing steps, clean-up and safety measurements.

Extracts processed with CO2 technology are also more desirable than extractsprocessed with other solvents. Supercritical fluid extraction with CO2 deliversthe most natural-smelling and -tasting extracts because there are no volatilesremoved in a residual solvent removal post-processing step. Additionally,because CO2 processing requires low temperatures, there is less deterioration ofheat-sensitive components in the extract. Furthermore, since there is no oxygenin the process, the potential for oxidation of the extract is significantlyminimized.

A broad range of selectivity and dissolving power can be obtained insupercritical fluid extraction just by manipulating the operating conditionssuchas pressure and temperatureallowing targeting of specific compounds ofinterest. This tuning capability is extremely important because recent trends inthe herbal industry indicate an extract is often more effective and much saferto use than the whole herb itself. Studies comparing supercritical fluidextraction and alcohol extraction indicate that the overall extraction yieldobtained by alcohol solvents is often higher. However, the reason cited isbecause unwanted compounds such as waxes, tannins and chlorophyll are alsoextracted. In other words, the total volume extracted may be greater withalcohol solvents but the percentage of desired active compound in that extractmay be lower. Since supercritical fluid extraction is highly selective, thepurity of the desired active compounds in the total extract is higher and closerto the total yield, leaving much less waste and no need for additionalprocessing steps.

This has benefits for an array of products. For instance, many spices areknown for their therapeutic value. The active ingredients present in such spicescan be grouped in two categories. The volatile fraction essential oilsisresponsible for the flavor of the spice, while the nonvolatile fractionoleoresinscontainsmost of the compounds responsible for the spices medicinal attributes. Asopposed to processing with organic solvents or by steam distillation,supercritical fluid technology can, in a single step, selectively extract theoleoresin and essential oil fractions and then separate them by sequentialdepressurization. Furthermore, most raffinates (i.e., the material left overafter extraction) have a highly marketable value due to the content of fiber andprotein, which are not soluble in CO2. Several spices, including clove, fennel,paprika, ginger, nutmeg and chili, are processed commercially usingsupercritical fluid extraction.

One important group of bioactive compounds is antioxidants. The antioxidantsused in the food industry can be grouped into natural antioxidants and syntheticantioxidants, with the latter including butylated hydroxyanisole (BHA),butylated hydroxytoluene (BHT), tertiary butylhydroquinone (THBQ) and propylgallate (PG). Both types of antioxidants play a very important role in the foodmarket. The driving force behind their prominent role is the demand for naturalfood ingredients free of chemical additives. Some herbs and spices exhibitantioxidant properties, including rosemary, sage, oregano, thyme, clove,allspice and black pepper.

Traditional extraction methods such as solvent extraction, aqueous alkalineextraction and steam distillation are not selective, so antioxidant extractsoften show color (chlorophyll) and have a strong flavor. Therefore, furtherpurification steps are often required for the extract and final food product toremove unwanted residuals. Supercritical CO2 extraction, on the other hand,inherently increases selectivity and allows for fractionation of the extract.For example, the active compound in rosemary can be extracted with supercriticalCO2 into two fractions by modifying pressure and temperature. The first fractionincludes the antioxidants (carnosol and carsonic acid), which can be enriched bysupercritical CO2 to high concentrations without chlorophyll, while the secondfraction is mainly essential oils.

In addition to their properties as natural food colors, carotenoids also playan important role as food ingredients due to their provitamin A activity andantioxidant function. Carotenoids, however, may be oxidized in traditionalprocessing. In most cases, supercritical fluid extraction reduces the potentialfor oxidation. Also, since CO2 has a low critical temperature, it caneffectively process thermolabile carotenoids.

Lutein obtained from marigold flowers and astaxanthin from algae are twocarotenoid products on the market utilizing supercritical fluid technology.

Supercritical fluid technology offers tremendous advantages, such as theabsence of any organic solvent residues and selective extraction andfractionation of different compounds. All of these advantages are almostimpossible to obtain easily from conventional processes at low operating costs.Therefore, supercritical fluid technology is an ideal tool for the processing ofactive compounds for use in food products and dietary supplements.

Jose L. Martinez, Ph.D., is the application and lab manager at TharTechnologies, a leader in the development of supercritical fluid process andequipment technologies. Thar Technologies (www.thartech.com)is based in Pittsburgh and is exhibiting at SupplySide East, Booth #1310.