708
Unit 7 Working with Complex Food Systems
Separating with Solvents
One chemical method of separating foods is treatment with a
solvent. Solvents are used to remove a desired component from a
food. An example is the use of hexane to maximize the amount of
oil removed from plant sources. Hexane is a nonpolar solvent that
is percolated through pressed seeds like corn, cottonseeds, and
soybeans. The oil dissolves in the hexane and is carried away from
the seeds. The hexane is then distilled off the oil and collected to
be reused.
The Chemical
Separation of
Lactic Acid
STEM
Lactic acid is an additive in many
foods and beverages. It provides a
good example of the procedures that can be
involved in separating food components for
commercial use. There are seven chemical
separation steps involved in producing pure
lactic acid from whey.
1. Whey is separated from cheese curds
through precipitation.
• The whey is placed in sterilized
19,000 to 38,000 L (5,000 to
10,000 gallon) wooden tanks.
• The whey is inoculated with
Lactobacilli, a specialized strain
of bacteria.
• Calcium hydroxide is added
periodically to keep the mixture
from becoming too acidic.
2. Lactic acid is separated from the whey
through precipitation and fi ltration.
• Sulfuric acid is added. It reacts with
the calcium and lactic acid to form the
precipitate calcium lactate. Calcium
lactate is a salt that forms crystals.
3. In purer grades, calcium lactate
is separated from the whey by
concentration and precipitation.
4. The calcium lactate is dissolved in water
then recrystallized to purify it.
5. The calcium lactate is dissolved and the
solvent, methanol, is pumped through
the liquid. Methyl lactate is distilled out
of the calcium lactate solution.
6. The methyl lactate is hydrolyzed to
produce pure lactic acid and methanol.
7. The methanol is separated from the
lactic acid through distillation. The
methanol is then recycled. The physical
design and careful monitoring of this
step are critical as methanol is extremely
toxic if consumed in suffi cient quantities.