Advancements in Oil and Oilseed Processing - Food and Industrial Bioproducts and Bioprocessing - page 126

collected from the process increased as the ultrasonic power increased possibly due to larger
amount of neutral oil entrainment in the gum (Moulton and Mounts, 1990).

4.4.1.2 Membrane degumming

Membrane degumming of crude oils has also been reported (Moulton and Mounts, 1990;
Young et al ., 1994). Membrane processing is simple, consumes less energy than other
degumming techniques, can be carried out at ambient temperature and retains nutrients and
other desirable compounds in the degummed oil (Raman et al ., 1996 ). Utilization of
ultrafiltration systems equipped with hexane-resistant membranes for degumming hexane-
oil miscella has been studied (Iwama, 1987; Gupta, 1977). Two membranes (DS-7 and
AN03) were evaluated for their flux and rejection properties. A 99.6% rejection of PLs was
achieved at 20.4 Bar and 40 °C by using DS-7 membrane; significant reduction in the color
of the oil was also observed after membrane processing (Lin et al ., 1997 ). A number of
ultrafiltration membranes prepared in the laboratory were tested for their PLs rejection.
A pilot scale study demonstrated that 93% PLs rejection was possible when vegetable oils
were processed without adding a solvent to reduce viscosity (Zhang et al ., 1996 ). The
microfiltration membranes made of PTFE and PVDF (polyvinylidenefluoride) have also
been shown to be effective in rejecting PLs. Although, in general, hydrophobic membranes
are preferred for oil processing, hydrophilic PTFE membranes with 100 nm pore size
were also successfully used for oil degumming without any compromise in flux rates
(Subramanian et al ., 1999 ). Non-porous composite polymeric membranes have selectively
rejected PLs (97.4-99.9% PLs rejection), resulting in less than 240 ppm phosphorous in the
permeate without any pretreatment or dilution of crude oil with organic solvent. It was also
reported that the permeate flux needed improvement before industrial adoption of non-
porous membranes for oil degumming (Subramanian and Nakajima, 1997).
An interesting approach, surfactant-aided membrane degumming, has been reported to
improve membrane degumming of soybean and rapeseed oils (Subramanian et al ., 1999 ).
The hydration rates of different phospholipids, phosphatidylcholine (PC), phosphatidylin-
ositol (PI), phosphatidylethanolamine (PE) and phosphatidic acid (PA), were reported to be
in the magnitude of 100, 44, 16, and 8.5 on an arbitrary scale of 100 (Segers and van der
Sande, 1990). Calcium salts of PE and PA had very poor hydration rates of less than one on
the above scale. It was also reported that fast-hydrating PLs such as PC had the ability to
encapsulate other phospholipids. The effect of soybean lecithin addition into crude oil prior
to degumming by using a porous polymeric membrane has been evaluated. A PLs reduction
of 85.8-92.8% in soybean oil was achieved during membrane processing. The phosphorus
content in the permeate varied between 20 and 58 ppm depending on the processing
conditions (Subramanian et al ., 1999 ).
High temperature durability, mechanical strength, chemical inertness, organic solvent
resistance and unique surface characteristics are some of the advantages of ceramic
membranes as compared to polymeric membranes. These membranes are also resistant to
microbial growth and steam sterilization. Utilization of ceramic membranes for oil
degumming has been examined (De et al ., 1998 ; Ribeiro et al ., 2008 ). Soybean oil
degumming in oil/hexane miscella by using a multichannel ceramic membrane resulted in
99.7% PLs retention and 2.2 ppm phosphorous in the permeate (Ribeiro et al ., 2008 ).
The main limitations of conventional membrane processing are short membrane life,
low temperature and pressure ranges for polymeric membranes, sensitivity of membranes to
chlorine, and instability of membranes at high and low pH ranges. Membrane oil degumming