**1. Introduction**

There are several old and new applications for the supercritical fluid (SCF) technology in bioprocessing, including the nonthermal cell inactivation (Dillow et al., 1999; Spilimbergo and Bertucco, 2003; Hong and Pyun, 2001), permeabilization (Aaltonen and Rantakyla, 1991), extraction of fermentation products (Bruno et al., 1993; Hampson and Ashby, 1999; Isenschmid et al., 1995), removal of biostatic agents and organic solvents from fermentation broth, SCF disruption of yeasts (Castor and Hong et al., 1995; Lin and Chen, 1994; Lin et al., 1992; Nakamura et al., 1994) and bacteria (Juhasz et al., 2003; Khosravi- Darani et al., 2004), destruction of industrial waste (Kim and Hong, 2001), fractionatation and purification of biopolymers (Khosravi- Darani et al., 2003), removal of chlorinated compounds from water, and treatment of lignocellulosic materials (Puri, 1983). Some products possibly produced by the SCF technology may be found in processes to obtain vitamin additives, de-alcoholized beverages, de-fat potato chips, and encapsulated liquids. For more information on the other examples, the readers are referred to the literature (King and Bott, 1993; Brunner, 2005; McHugh and Krukonis, 1994; Bertucco and Spilimbergo, 2001). Khosravi-Darani et al. have reviewed all aspects of the supercritical fluid extraction (SCE) in the downstream processing of bioscience (Khosravi-Darani and Vasheghani-Farahani, 2005).

There are also several applications for the SCF technology in food engineering including: extraction of compounds from natural products (the processing of hops, the extraction of caffeine, vanilla, beta-carotene, and vegetable oils), food sterilization, removal of undesired extractable (pesticides residues, hazardous chemicals from fish tissue, oil from dry-milled corn germ), and fractionation of cod liver oil (Bruno et al., 1993). Catalytic reactions in supercritical CO2 have been receiving an increased attention during the last decade (Sarkari et al., 1993).

This chapter has focused on SCF special applications in the field of food biotechnology. The application of SCF is simple, inexpensive, and noninjurious to the structure and function of enzymes (Lin et al., 1992) and protein activities (Kamat et al., 1995; Zheng and Tsao, 1996; Kasche et al., 1988). The supercritical carbon dioxide (SC-CO2) is the most commonly used

Supercritical Fluid Application in Food and Bioprocess Technology 557

Low-value, High-volume (LVHV) products (Vijayan et al., 1994). The production of HVHV has been found to be very favorable for the exploitation of the SFE technology. The types of foods processed include: flavor, fragrance, spice extracts, and essential oils from plants (Wang and Muttucumaru, 2002), animals, and other materials; hop extraction to produce alpha and beta acids as well as essential oils; purification and fractionation of aroma constituents. In fact, the advent of food processing as a modern industry has ushered in the

The food extractives of spices, called oleoresins, are used in the food processing industry for their appealing flavor and to improve the product quality. The selectivity of the extraction can be achieved using SC-CO2 and the essential oils of pepper and ginger can be extracted without much contamination of non-volatile matter by the suitable selection of the extraction pressure and temperature of CO2 (Nguyen et al., 1994). In the SCE of ginger, the oxygenated fraction can be much higher than that in steam-distilled oils. The ginger-oils in oleoresin of ginger can be extracted without any decomposition. The piperine can be extracted with insignificant loss with longer process times. The jasmine and vanilla absolutes from this process have desirable top notes with rounded flavor and are superior to those obtained by conventional process. Examples for IVIV include: the removal of caffeine from coffee and tea; the xanthins from cocoa; excess oil from fried foods and vegetable. Studies on reducing the cholesterol content of animal fats and the extraction of lipids are in progress. Separation of the polyunsaturated fatty acids (PUFA), notably eicosapentacnoic acid (EPA) and decosahexanoic acid (DHA), which are purported to have beneficial physiological activity, from a mixture of fatty acid and ethyl esters from fish oils is reported (Hammam, 1992). With respect to the SFE of LVHV products, there are some doubts as to whether it is competitive with traditional extraction methods, e.g., the oil production from vegetable seeds; the processing of grain flours to improve quality and fractionation of beef tallow.

Table 1 shows some valuable extractives from natural materials in food industry.

measured by HPLC and GC/MS (Wang and Muttucumaru, 2002).

**4. The inactivation of food related bacteria** 

The SFE process parameters including pressure and temperature variations have been

The application of high pressure ranging from 100 to 1000 MPa, is one of the most promising methods for the food treatment and preservation at room temperature (Debs-Louka et al., 1999). High pressure inactivation of *E. coli* pressure resistant had been investigated in fruit juices and in low pH buffers. The results show that both parents and mutant strains become more pressure-sensitive in decreased pH and presence of organic acids. The high pressure treatment for 5–10 min under 300–600 MPa at 20–50°C allows the reduction of vegetative microbial cells by 4–5 log cycles. However, some enzymes, especially polyphenoloxidase in fruit juices, are more pressure-resistant and their inactivation needs additional approaches (Molin, 1983). The degradation of color and slight changes of flavor due to the higher content of dissolved oxygen in products are mentioned as an example of negative pressure effects (Knorr, 1995). Pasteurization of milk and the heat resistance of *Mycobacterium avium* subsp *paratuberculosis* (Lund et al., 2002) also vegetative and the latent form of other microorganisms have been reviewed (Sojka and Ludwig et al., 1997; Paidhungat et al., 2002; Raso et al., 1998). It seems evident that it was not possible to kill spores at room temperature with an extremely high operating pressure, up to 170 MPa. It was observed that there is an optimum range of temperature and pressure for stimulating

use of food extractives rather than raw materials.

fluid. It's low critical temperature of 31.1°C and the pressure of 7.3 MPa make it an ideal medium for processing volatile products (Wells and DeSimone, 2001). The non-toxicity, non-flammability, as well as the selectivity of the process and the ease of recovery are the most important features. Most of SCFs are available in a relatively pure grade at a reasonable cost as compared with the industrial grade liquid solvents. Therefore, many subsequent downstream clean-up steps are unnecessary supercritical extraction (SCE). By replacing the SCE to avoid liquid extraction, O2 is always very efficiently displaced from the matrix. This prevents oxidation and autoxidation reactions from becoming a problem, as they are often in liquid extraction schemes. This fact is a particular advantage in biotechnology since many important natural products and drugs are oxygen-sensitive (Teja and Eckert, 2000).

There are also some limitations in the SCF applications e. g. change of the phase equilibrium; alter of phase diagram of the solvent, difficult prediction and design of extraction conditions; necessity for addition of impurities as modifiers (called entrainers or cosolvents) to SCF in quantities up to 5(%v/v); impossible real time control by the most accurate equations of state, necessity to unfired pressure vessels; high initial capital outlay due to the high cost of compressors (Bruno et al., 1993). Other applications of the SCF in food biotechnology can be summarized as follows: removal of fat; alcohol recovery from wine (Guvenc et al., 1998); encapsulation of liquids (Heremans and Smeller, 1998), recovery of tocochromanols (vitamin E) and beta-carotene (provitamin A).

Particulate products can be also achieved by means of SCF processing e.g. concentrated powder after spraying of CO2–liquid mixture into a spraying chamber at ambient conditions together with the substrate; also flash release of CO2 from the liquid will result in the formation of small droplets. The prevention of oxidation processes and easier handling, dosage, and storage are among the purported advantages of this process (Brunner, 2005).
