Advancements in Oil and Oilseed Processing - Food and Industrial Bioproducts and Bioprocessing - page 131

suitable catalyst for FFA esterification. FFA concentration in very high FFA content oils
(about 40%) could be significantly reduced (to less than 10%, usually 1-3%) by chemical
esterification (Bhattacharyya and Bhattacharyya, 1987). Although this process is technically
feasible, it is not cost competitive with physical refining process and has not been
commercialized yet (De and Bhattacharyya, 1999; Bhosle and Subramanian, 2005).

4.4.2.7 Removal of FFAs with supercritical fluids

Supercritical CO 2 has been used to remove FFAs from oils. Selectivity of SC-CO 2 for FFAs
is higher than that for TAGs at lower pressures. Based on this concept, different processing
schemes have been proposed to extract FFAs and refine oils using SC-CO 2 . One approach
involves a two-step process during which FFAs, unsaponifiable matter and tocopherols are
extracted at low pressure before the TAGs remaining in the feed material are recovered with
SC-CO 2 at a higher pressure (Zhao et al ., 2000). The disadvantage of this process is that
health beneficial bioactive compounds such as tocopherols end up in FFAs rather than TAGs
which is the product used for edible applications.
A patented process describes a continuous countercurrent SC-CO 2 fractionation
technique for deacidification of crude vegetable oils using a packed column (Dunford and
King, 2004). Fractionation at low pressure (138 Bar) and high temperature (80 °C) was
effective in removing FFAs from crude rice bran oil without any oryzanol loss in the extract
fraction (Dunford and King, 2000, 2001; Dunford et al ., 2002 ). A columnar fractionation
technique was also successful in removing FFAs from crude wheat germ oil and
concentrating health beneficial bioactive compounds in the TAGs fraction (Eisenmenger
et al ., 2006). Deacidification of soybean oil deodorizer distillate could be achieved using
SC-CO 2 technology (King and Dunford, 2001). Lampante olive oil refining (Bondioli
et al ., 1992) and deacidification of roasted peanut (Ziegler and Liaw, 1993) and olive oil
(Brunetti et al ., 1989 ) using the SC-CO 2 technique have also been demonstrated. These
studies showed that FFA solubility in SC-CO 2 was directly related to the degree of
unsaturation and deodorization was mass transfer controlled, while deacidification was
thermodynamically constrained.
Supercritical CO 2 is an excellent solvent to remove FFAs from crude oil. The capital and
processing costs of a SC-CO 2 deacidification process would be relatively lower than those
for oil extraction because of the higher solubility and selectivity of FFAs in SC-CO 2 at lower
pressures than those of TAGs. Certainly this technology has a lot of potential for oil refining,
specifically for high value specialty products.

4.4.2.8 Removal of FFA by adsorption

Adsorption processes have also been examined to remove FFAs from oils. A process
which utilizes magnesium oxide as adsorbent to remove FFAs from oils has been patented
(Munson et al ., 1995). Aluminum hydroxide gel is also effective for removing FFAs.
Mechanically expressed soybean oil was successfully deacidified by using Magnesol ® ,
a commercial adsorbent designed to remove FFA from oils. The FFA content of the oil
was reduced to 0.04% by adsorption with 3% Magnesol ® . This material also adsorbed
primary and secondary oil oxidation products. The Magnesol refining process was much
milder than conventional refining, as evidenced by very small amount of primary and
secondary lipid oxidation product formation and less loss of tocopherols (Wang and
Johnson, 2001 ).