Food Biochemistry and Food Processing (2 edition)

BLBS102-c40 BLBS102-Simpson March 21, 2012 14:23 Trim: 276mm X 219mm Printer Name: Yet to Come

772 Part 7: Food Processing

Pumps

3-stage extraction columns

2-stage separation vessels

Storage tank

CO 2 inlet Co-solvent inlet

Figure 40.4.Schematic diagram of commercial scale multistage supercritical fluid extraction system used to fractionate bioactive

components. The symbol “” is pressure valves and “ ” is heat exchangers.

vessel, because the process is switched to the next prepared

vessel by control valves for extraction while unloading and/or

loading the spent vessels. Thus, supercritical CO 2 technology

is available in the form of single-stage batch that could be

upgraded to multistage semi-continuous batch operations cou-

pled with a multi-separation process. The need to improve the

design into truly continuous modes is growing. Supercritical

CO 2 fluid extraction could be cost-effective under large-scale

production.

Industrial Applications

Large-scale supercritical CO 2 fluid extraction has become a

practical process for the extraction of high-value products from

natural materials. The solvating power of supercritical CO 2 flu-

ids is sensitive to temperature and pressure changes; thus, the

extraction parameters may be optimized to provide the highest

possible extraction yields with maximum antioxidant activity for

health-promoting components in bioactive extraction production

(Kasamma et al. 2008, Chen et al. 2009, Yi et al. 2009b).

A supercritical CO 2 fluid extraction process offers the unique

advantage of adding value to agricultural waste by extracting

bioactives from agricultural by-products, which are then used

for the fortification of foods and other applications. Its draw-

backs are the difficulties in extracting polar compounds and

its difficulty of extracting compounds from a complex matrix

where the phase interaction with the intrinsic properties of the

product inhibits its effectiveness. Some drawbacks can be ame-

liorated by using small amounts of food-grade co-solvents (less

than 10%) to approach the high extraction efficiency (Shi et al.

2009a). However, much investigation is required to understand

the solvation effects on the targeted bioactive components be-

ing extracted. The CO 2 density, pressure, and temperature have

been noted to have great impacts on the results of the extraction

process. By understanding the effect of the parameters that influ-

ence the extraction process, the conditions may be set to optimize

yield and cost efficiency. When determining the parameters that

should be used to maximize yields and solubility of the targeted

components, many researchers attempted to use conditions that

may be applicable in large-scale applications (Shi et al. 2007f,

Kasamma et al. 2008). For example, nontoxic co-solvents and

modifiers could be acceptable for food processing; therefore, a

number of researchers have opted to use food-grade co-solvents

and modifiers in extraction processes (Shi et al. 2009a). The na-

ture of the material used as a source of high-value components,

such as health-promoting components, governs the availability

of the compounds for the extraction process. The presence of

other components such as lipids may impede the process or

elevate costs due to an elongated extraction time.

Although a high temperature in the extraction process gen-

erally increases the solubility of components in supercritical

CO 2 fluids, the conditions under which thermally labile targeted

compounds are negatively affected should be considered (Shi

et al. 2007a, 2007b, 2007e). The intensity and the length of heat

processing affect the health-promoting properties of bioactives.

Therefore, ideally, the extraction time and temperature should

be minimized. Minimizing such conditions also leads to a more

economically viable process (Shi et al. 2007f, Kasamma et al.

2008). Excessively high flow rates may reduce the contact time

between the solute and the solvent and restrict the fluid flow

in the sample if it becomes compacted. The optimal flow rate

appears to vary with the targeted molecule, relatively high flow

rates having a negative effect on some components. Raising the

pressure increases extraction yields.

Sample matrix is an important parameter that influences the

solubility and mass transfer process during SCE. Properties such