Advancements in Oil and Oilseed Processing - Food and Industrial Bioproducts and Bioprocessing - page 125

characteristics (affinity to lipids), become oil insoluble and agglomerate into a gum phase.
Gum is separated by centrifugation and added back to meal or further processed to produce
lecithin, which is used as an emulsifier in food and feed applications. In industry the PL
concentration of oil is expressed as parts per million (ppm or mg/kg oil) phosphorous, which
can be converted to phospholipids by using the relationship:

4

%PLs = [(Phosphorous in oil, ppm) × 31.7)] × 10

The residual phosphorous level in degummed oil is usually around 100 mg/kg oil after
water degumming. PL content of the oil can be further decreased (30-50 mg/kg) in a process
called super-degumming by adding organic acid (1500-2500 mg/kg) into the oil at 40-55 °C
(Segers, 1982). A newer process, “Ultra Degumming” utilizes an ultra-sheer mixer to attain
shear forces around 100 000 sec -1 to enhance oil-acid-water contact and reduces the phos-
phorous content of the oil to 5 ppm (Gupta, 2008). Degummed oil is cooled to below 40 °C
before entering a feed tank for further refining.
The “Total Degumming (TOP)” process is similar to the “Ultra Degumming” and
utilizes a high-shear mixer to bring previously water degummed oil-acid-water mixture
into close contact. An average acid droplet size well below 10 μm, equivalent to at least
10 million acid droplets per gram oil, is attained by high shear mixing. After a sufficient
contact time, a base is added and mixed into the acid-in-oil dispersion to adjust the pH
of the aqueous phase between 2.5 and 7.0 (Xu and Diosady, 2004). An emulsion forms
with minimal soap formation. During the process the acid initially dissociates metal/
phosphatidic acid (PA) complexes into insoluble metal salts and PA (in acid form). PA is
then hydrated by partial neutralization with the base added, and removed from the oil by
centrifugation. Another version of the same process utilizes two centrifuges to remove
the hydrated PLs with a high efficiency and minimal losses. The first centrifuge removes
the bulk of the gum phase. Since the gums are sticky and very viscous, some PLs still
remain in the oil after first centrifugation. The second centrifuge removes the remaining
gums in the oil. The gums recovered from the second centrifuge are recycled to the
process because of their high oil content. After degumming, the oil is washed with water
to remove residual phosphorus salts and acid. The process produces a low phosphorous
(about 5 ppm) and iron (<0.1 ppm) oil, but when a water-degummed oil has a higher
Ca/Mg content, TOP becomes less effective (Xu and Diosady, 2004). The investment
cost for the TOP process is high because of the use of two centrifuges. The process has
been combined with alkali refining and named “integrated TOP”, where another base is
added to the oil immediately after the degumming stage but before water washing, to
extract fatty acids and save costs.
The “SOFT degumming” process removes non-hydratable PLs by using a chelating
agent (i.e. EDTA), which forms complexes with Ca 2+ and Mg 2+ salts of PA and improves
interfacial exchange properties (Choukri et al ., 2001). This process produces degummed oil
with low residual phosphorous (<5 ppm) and iron (<0.05 ppm) contents.
Ultrasonic or acoustic cavitation occurs when a liquid is subjected to high intensity sound
waves (20-10 MHz). This causes the formation, growth and rapid recompression of vapor
bubbles in the liquid. The implosive bubble collapse generates localized heat and pressure
and produces intimate contact among liquid components. The effect of ultrasonic cavitation
on PL removal was examined in a continuous degumming system. It was found that
phosphorous removal varied between 90 and 99% depending on the ultrasonic power
applied. Low power (22 watts) resulted in higher PL removal. The weight of the gum