By Dr. Sajilata Gopalakrishnan, Chief Scientific Officer, Nature Pure Supercritical Extracts Pvt. Ltd.
With the rising concerns over the use of synthetic ingredients and the negative impact with respect to their recurrent use on health, the use of natural ingredients for the coloring and flavoring of foods, cosmetics, and pharmaceutical products is gaining much importance on the international front. A residual solvent-free and an environmentally compatible fluid such as CO2 is an attractive alternative to the use of solvents such as hexane and ethyl acetate for the extraction of active components of biological significance and natural ingredients for the desired visual and flavor appeal. Carbon dioxide (CO2), the most tapped supercritical fluid (SF) in the industry, is non-toxic and non-combustible. With a critical temperature of 31.06°C and critical pressure of 7.386 MPa (73 bar), the energy costs associated with using CO2 as an extraction solvent are lower than those of other fluids (water’s critical temperature and pressure are 374°C and 220 bar, respectively).
In supercritical fluid extraction (SFE), when a feed material such as ground spice is brought in contact with supercritical CO2 (SC-CO2), the active substances such as the spice oils and the oleoresins from the matrix gradually partition into the supercritical phase. When the required extraction efficacy has been met, the extracted components are separated from the SF by pressure reduction. Essentially, this lowers the fluid’s solubilizing power and precipitates the extracted substance. The SF may then be recompressed to the desired extraction conditions and recycled.
In comparison to the conventional steam distillation techniques, SFE results in high yields and quality of essential oils and natural aroma. While the conventional steam distillation or solvent extraction techniques involve high temperatures degrading the heat-sensitive natural products, SFE operates at near ambient temperatures, ensuring that the natural components are retained to produce extracts with characteristics very close to the natural profile of the raw material. The essential oils extracted using CO2 are superior to the steam distilled ones in that the terpene esters, which play a significant role in determining the flavor profile, are not hydrolyzed, for e.g. steam distillation produces clove oil with low yields of eugenyl acetate owing to the hydrolysis of eugenyl acetate to eugenol, whereas the clove oil obtained using SFE contains higher amounts of eugenol and eugenyl acetate.
Natural flavors from cinnamon and cardamom essential oils may be used in flavored milk. A blend of cinnamon, clove, and black pepper flavors is very effective for ice cream. Ginger oil and oleoresin are flavouring ingredients for buttermilk. The oil or oleoresin may be microencapsulated in the powder form by spray drying with emulsifiers. Roasted coffee bean oil is of commercial importance owing to the rich aroma of roasted coffee beans and may find applications in ice cream. The nutty flavor of pumpkin seed oil goes well with ice cream. Pumpkin seed oil contains biologically active substances such as carotenoids, tocopherols, and polyunsaturated fatty acids. Also, the CO2 lipid extract from pumpkin seeds is a good source of vitamin E (37 mg/100g), which is a strong antioxidant against free radicals. Vanilla extracts find applications in puddings, yoghurt, ice cream, and milk beverages. The extracts work well in combination with chocolate, butter, and fruit flavors. The CO2 vanilla extracts are more than 150 times powerful than the standard single-fold vanilla extracts and are preferred over the alcoholic counterparts.
Organic foods typically use β-carotene for a red-orange to yellow color, paprika for a red-orange color, or curcumin  for a yellow shade in foods. Natural food colors may be extracted from the seeds of annatto (Bixa orellana L.) using SC-CO2. Annatto pigments impart a yellow or orange color to cheese, dairy spreads, butter, margarine, and other dairy products.
Spice oleoresins are free of bacterial contamination, have a long shelf life, and are a convenient substitute for ground spices. Oleoresins have low moisture contents, are free from extraneous impurities, and deliver instant flavor release at low dosages. Paprika extract is manufactured by solvent extraction or CO2 extraction of the dried Capsicum annum pods. The extract is mainly composed of the red carotenoid pigments, capsanthin and capsorubin, and the extracted or added vegetable oil. The colored extracts are viscous, homogenous liquids that impart a deep red color to foods containing a lipid phase. Commercial paprika coloring extract is available in different color strengths up to 1,50,000 color units (CU), equivalent to about 10.8% total carotenoids. 1 kg of paprika extract can replace around 14 kg of paprika powder with respect to color intensity. Typical usage levels of the pure coloring matter range from 10 – 60 ppm of the finished product. The extract may be used in dairy products such as yogurt, whey-based drinks, ripened cheese, pudding, ice cream, and fruit- or flavored yogurt. The SC-CO2 extraction of red chilli (Capsicum frutescens) in the pressure range of 300-500 bar and 80-100 °C yields two fractions; the light fraction contains capsaicin for pungency, while the heavy fraction consists of triglycerides and the colored carotenoids. The Indian cheese, paneer, may be flavored and colored with paprika extract.
Curcumin may be used to color margarine, cheese, butter, and other food products. Turmeric (Curcuma longa) rhizomes extracted with pure CO2 and an entrainer such as ethanol results in an oleoresin containing 37-55% curcumin, out of which 95% curcumin may be crystallized.
Dairy products rich in polyunsaturated fatty acids and esters are prone to oxidation, leading to loss of color and nutritive value, loss of flavor or development of off-flavors, and the accumulation of undesirable compounds, which may be detrimental to health. Synthetic antioxidants such as butylated hydroxyanisole (BHA) and propyl gallate are usually used to retard oxidation. The use of natural antioxidants is gaining much importance in the food industry with rosemary being tapped as a natural antioxidant in dairy products to reduce the rate of lipid oxidation and hydrolysis, thereby enhancing the shelf life of the products. The antioxidant activity of rosemary extracts is due to the two phenolic diterpenes, carnosic acid and carnosol. The compounds effecting antimicrobial activity are α-pinene, bornyl acetate, camphor, and 1,8-cineole. SC-CO2 extracts of rosemary have been shown to be promising ingredients with regard to their natural aroma, color, and antioxidant potential in foods, cosmetics, and pharmaceutical products.
SFE using CO2 is thus a safe, cost-effective, and attractive separation technique for the industry owing to a growing demand for processes that do not introduce any residual organic solvents into the final product. A main industrial interest in the use of SF for the extraction of natural components is the ability to undertake the extraction at low temperatures and thereby prevent the thermal decomposition of extracts and preserve the required natural properties. Moreover, with the approval and recognition of the use of SF by regulatory bodies, it is imperative that SC-CO2 is a promising and inevitable green solvent of the future.
