Food Lipids: Chemistry, Nutrition, and Biotechnology

Figure 14 Steps in refining and converting edible oils.
storage or in the headspace. Degumming may be conducted either as a separate
operation or simultaneously with neutralization. In the cases of oils rich in phosphatides,
such as soybean and canola oils, degumming is usually a separate operation.
Hydration makes phosphatides insoluble in the oil, and they precipitate, yielding an
oil that is unattractive because of unsightly sludge or gums. Phosphatides can degrade
and cause dark colors when the oil is heated as in the later deodorization step. All
soybean oil in the export trade is degummed [38]. Phosphatides are also surfactants
and, if present in frying oils, can cause dangerous foaming. When hot oil foams up
and spills over the rim of a cooking vessel, it may burn the user; if it contacts a
flame, it will catch fire. Phosphatides, also known as lecithin, are important food
emulsifiers and, in the case of soybean oil, oftentimes become economical to recover.
The gums are rendered insoluble in oil by hydrating them with 1–3% water.
As a general rule, the amount of water should be equivalent to the hydratable phosphatide
content of the oil. If single-bleached lecithin is to be recovered, then hydrogen
peroxide may be added to the water; if double-bleached lecithin is to be recovered,
then benzoyl peroxide may also be added [39]. Alternatively, the degummed
lecithin alone may be treated with hydrogen peroxide or both. The mixture is intensively
mixed and then agitated for 30–60 minutes at 60–80�C in a slow mixing
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