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Handbook of Functional Lipids

phospholipids prior to the bleaching step. The bleached oil is then steam distilled
to remove FFAs. This is a normal operation of a deodorizer. The physical refining
process has numerous advantages; it is a simpler and less costly process and has a
reduced wastewater load.

5.3.1.3 Miscella Refining (Caustic Refining

in the Presence of Solvent)

The final oil concentration of the miscella at the end of extraction is usually around
20 to 25% by weight. After going through the initial evaporator, the concentration
of oil in the miscella is increased to close to 40 to 50%. In miscella refining, the
concentrated miscella is then refined with caustic soda (16 to 24 degree Be

). The

FFAs in the oil react with the sodium hydroxide in a continuous tubular mixer and
reactor at 130 to 135

F (54 to 57

C). The refined oil in the solvent is then separated

from the soap by centrifugation prior to entering the second stage evaporator and
mineral oil scrubber. The once-refined oil should then have less than 80 ppm residual
solvent and be ready for bleaching and deodorization or other further processing.
In recent years, oilseed extraction mills have been motivated to use miscella refining
because of improved neutral oil yield, more consistent oil color, and elimination of
water washing when this process is used.

5.3.2 B

LEACHING

The oil is further purified by bleaching, which removes color bodies and trace metals,
as well as entrained soaps and some oxidized products that are adsorbed into the
surface of bleaching agents or adsorbents. This improves the appearance, flavor,
taste, and stability of the final product. Types of adsorbents most commonly used
include neutral clay, acid activated clay, and activated carbon. The choice of adsor-
bent will depend on a balance between activity of the adsorbent, oil retention loss,
and adsorbent cost.

The process is generally carried out via batch or continuous bleaching. Adsorbent

(e.g., bentonite clay) is mixed with the refined oil creating a slurry that is agitated
to enhance contact between the oil and the adsorbent. This is generally carried out
under a vacuum at 90 to 95

C (194 to 203

F) for 15 to 30 min. Vacuum bleaching

offers the advantages of an oil with improved oxidative and flavor stability. Finally,
the adsorbent is filtered from the oil using pressure leaf filters precoated with
diatomaceous earth. Spent clay is steamed for efficient oil recovery.

5.3.3 W

INTERIZING

The term “winterization” derives from the observation that refined cottonseed oil,
stored in outside tanks during the winter months, will form a solid fraction. A batch
process to mimic the winterization process has been used for decades to fractionate
the solid portion of an oil (i.e., separate the higher melting fraction from the lower
melting fraction). This process is applied to ensure that the finished oil will not
easily become cloudy in cool storage conditions. The winterization process is commonly

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