Tips from A doctoral student in food science wanted to know if bio- diesel producers would be willing to pay a premium for distillers corn oil with a lower free fatty acid (FFA) content.
q: An article in the March 2016 issue of Inform reveals that
process contaminants are created when edible fats and
oils are exposed to high temperatures and long residence
times during traditional deodorization. It seems to me that a
molecular still could prevent, or at least minimize, formation
of harmful compounds, as the exposure to high temperatures is extremely short (a few seconds), compared to hours
of exposure during traditional deodorization. Why aren’t
wiped-film evaporators, short-path distillers, or molecular
stills commonly used for deodorizing edible fats and oils?
A: Here is a summary of the responses.
• Wiped-film evaporators or molecular stills are an order
of magnitude more expensive than the deodorizers used
today. In Southeast Asia, typical capacity requirements
are between 1,500– 3,000 tons per day of oil per deodorizer. Multiple wiped-film evaporators or molecular stills
would be needed to reach these capacity requirements,
which would drive up capital expenditures. With palm
oil, more time under high temperature is needed to
break down the color and enable the oil to become volatile enough to be stripped. Typically, one hour of residence time under high temperature is required to meet
the market demand for oil that is low in (red) color. This
long residence time is practical in a tray deodorizer, but
not in a wiped-film evaporator. When the temperature
and pressure conditions required to evaporate some of
the contaminants are reached, the monoglycerides and
diglycerides are then distilled away. This moves a significant portion of the yield from high- value palm oil to
lower-value palm fatty acid distillate, which has a significantly negative impact on refining margins.
• Molecular distillation was thought to be the best solution
for stripping/physical refining of high-free-fatty-acid (FFA)
rice bran oil (FFA as high as 30%). However, one such
installation in India with huge capital expenditures failed
measurably. Molecular distillation (short-path distilla-
tion) was very selective in removing the fatty acids and
other lipid moieties rapidly, based on molecular weight
as well as absolute pressure in the system, but in doing
so all the broken down color bodies were left behind in
the deodorized/de-acidified oil. The distilled fatty acids
produced were almost water- white, but the oil itself
was dark-colored and could not be reduced by solution,
as it was a totally "fixed color." It is true that forma-
tion of 3-MCPD esters is an issue, but the retention time
required is not for the heat-bleaching alone. Some oils
and specialty fats, such as cocoa butter and sal oil, con-
tain pesticides that can be removed only with a longer
retention at relatively low deodorization temperatures.
• Molecular distillation is a fantastic simple unit operation
for heat-sensitive materials like tocopherols and omega- 3
fatty acids. It is also good for smaller-capacity biodiesel distillation, as one can convert non-edible high-FFA oils into low
FFA oils by simple one step molecular distillation.
• Wiped-film/short-path distillation can help recover
some of the valuable nutraceuticals, such as tocopherols, tocotrienols, sesamin, and sterols that are lost during
refining. Wiped-film/short-path distillation has also contributed a lot to the recovery of eicosapentaenoic acid
(EPA)/docosahexaenoic acid (DHA) from fish oils, production of carotene-rich red palm oil, lecithin recovery, and
the distillation of fatty acids, methyl esters, and glycerine. Capital expenses and color reduction are big issues
when processing some high FFA oils by molecular distillation, but niche oils such as sesame, rice bran, and corn—
which have a high percentage of unsaponifiables and can
be of huge therapeutic value—can certainly be processed
by wiped film if we are willing relinquish the bias for low
color that has gripped the entire industry for many years.
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