**2. The effect of high pressure and temperature on food constituents**

High pressure (100–1000 MPa) affects biological constituents and systems. Several physicochemical properties of water are modified, such as density, ionic dissociation, pH, and the melting point of ice. The pressure-induced unfolding, aggregation, enzyme inactivation (e.g., of ATPase) and gelation of food proteins occurred due to effect on noncovalent bonds and interactions. Chemical reactions, macromolecular trans-conformations, changes in the membrane structure and the melting point are enhanced under pressure . Several of these phenomena, are involved in the high inactivation ratio of most vegetative microbial cells: gram negative bacteria, yeasts, complex viruses, molds, and gram-positive bacteria, in this decreasing order of sensitivity to pressure. Other parameters like pressure, holding time, temperature and the composition of medium influence this resistance. The pH has little influence, but high salt or sugar concentrations and low water contents, exert very strong baro-protective effects. Many other articles have also dealt with the stability of proteins as a function of pressure (Zagrobelny and Bright, 1992; Athes et al., 1998) and particularly with that of enzymes (Degraeve and Lemay, 1997; Marie-Olive et al., 2000).

### **3. The recovery and purification of biological products**

Vijayan et al. have broadly classified the process applications into three product segments: High-value, Low-volume (HVLV); Intermediate-value, Intermediate-volume (IVIV) and

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

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

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).

High pressure (100–1000 MPa) affects biological constituents and systems. Several physicochemical properties of water are modified, such as density, ionic dissociation, pH, and the melting point of ice. The pressure-induced unfolding, aggregation, enzyme inactivation (e.g., of ATPase) and gelation of food proteins occurred due to effect on noncovalent bonds and interactions. Chemical reactions, macromolecular trans-conformations, changes in the membrane structure and the melting point are enhanced under pressure . Several of these phenomena, are involved in the high inactivation ratio of most vegetative microbial cells: gram negative bacteria, yeasts, complex viruses, molds, and gram-positive bacteria, in this decreasing order of sensitivity to pressure. Other parameters like pressure, holding time, temperature and the composition of medium influence this resistance. The pH has little influence, but high salt or sugar concentrations and low water contents, exert very strong baro-protective effects. Many other articles have also dealt with the stability of proteins as a function of pressure (Zagrobelny and Bright, 1992; Athes et al., 1998) and particularly with that of enzymes (Degraeve and Lemay, 1997; Marie-Olive et al., 2000).

Vijayan et al. have broadly classified the process applications into three product segments: High-value, Low-volume (HVLV); Intermediate-value, Intermediate-volume (IVIV) and

**2. The effect of high pressure and temperature on food constituents** 

of tocochromanols (vitamin E) and beta-carotene (provitamin A).

**3. The recovery and purification of biological products** 

and Eckert, 2000).

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 use of food extractives rather than raw materials.

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.

The SFE process parameters including pressure and temperature variations have been measured by HPLC and GC/MS (Wang and Muttucumaru, 2002).
