Fdv

Dry test meter

Preheater

Figure 4. Column-type separation by supercritical fluids.

Intermediate Lower

High pressure pressure pressure

Feed

Feed

Compressor Residue

Separator 1 Separator 2

TProduct 1 T^ Product 2

Recycle

Compressor Residue

Figure 3. Typical process flow diagram of SCFE.

0 40

Temperature (°C)

Figure 5. Typical applications of SCFE.

0 40

Temperature (°C)

Figure 5. Typical applications of SCFE.

tions. Analysis of SCF operations applicable to the food industry, design and economic considerations, and optimization of SCFE operations have been discussed in the literature. The products of SCFE processes show different characteristics as compared with those obtained by traditional vacuum distillation processes. In general, the product quality of SCFE processes may or may not be superior to those produced by conventional methods.

COMMERCIAL APPLICATIONS Coffee

In the decaffeination process of coffee, green coffee beans are treated with C02. The coffee beans are not roasted prior to the extraction. Thus, the inherent moisture in the beans acts as a chemical agent to free the caffeine from its bound form (2). Presoaked green coffee beans are treated with C02 at 16 to 22 MPa. The C02 is continuously recycled until the caffeine diffuses out of the beans into the SC C02 phase. The caffeine is washed out with water at 70 to 90°C. Caffeine content in the bean can be decreased from the initial value in the range of 0.7 to 3% to a value as low as 0.02%.

Hop Extraction

The use of hop extracts by the brewing industry is a recent, commercial application of SC extractions. The soft resin constituents of hops that contain the flavor components, humulones and lupulones, are conventionally extracted with dichloromethane. This results in a pasty, dark-green to black-green mass. In addition, the dichloromethane must be removed by evaporation after the resins have been extracted. In contrast, SC C02 extraction of hops between 35 and 80°C and 80 to 300 atm results in an "olive-green, pasty extract with an intense aroma of hops" (10).

POTENTIAL APPLICATIONS Extraction of Flavors

As compared with conventional solvent extraction, SCFE could be a potential alternative to extract and fractionate flavors and fragrances from fermentation-induced and natural products (8,27). SC C02 has been used to extract the following materials: essential oils and piperine from black pepper, alkaloids from chili pepper, eugenol from cloves, cinnamic aldehyde from cinnamon, limonene and carvone from caraway, sesamin from sesame seeds, vanillin from vanilla pods, menthol and menthone from peppermint leaves, and geraniol and citronella from roses. Supercritical C02 was used for concentration of aroma and flavor compounds in citrus oils (28). Citrus oils, like many other essential oils, consist of mixtures of hydrocarbons of the terpene and sesquiterpene groups, oxygenated compounds, and nonvolatile residues. The compounds that provide much of the characteristic flavor are mostly oxygenated compounds that account for less than 4% of the orange oil. Thus, the concentration requirement is high and the amount of yield is relatively low.

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