712
Unit 7 Working with Complex Food Systems
Many colloids and macro-
molecules can pass through fi lter
paper. Special barriers are often
needed to remove these substances
from liquids.
New fi ltration materials do
not rely on pore and particle sizes
but on the type of polymer and
its chemical interactions with the
food compounds. For example,
scientists could use a polymer
that would cause hydrophilic and
hydrophobic reactions to block
unwanted elements from passing
through the fi lter. This new method
is called nanofi ltration. Though soy
contains high-quality protein
and fat, it also has less desirable
compounds. Nanofi ltration has
allowed researchers to separate the
good from the bad. This technology
enables engineers to manipulate
fl avor, color, and other aspects of
foods. Scientists hope to use this
new technology to isolate phyto-
chemicals from functional foods.
Osmosis
When separation is needed
at the molecular level, osmosis
is one process that can be used.
Osmosis is the movement of a
solvent through a semipermeable
membrane. The solvent moves
from an area of low solute
concentration to an area of
high solute concentration. A
semipermeable membrane is a
thin layer of material that allows
some substances to pass through
but not others.
Two sugar solutions separated
by a semipermeable membrane are
illustrated in 23-7. The solution on
the left has a mass percent of 10.
The solution on the right has a mass
percent of 20. The membrane allows
Osmosis
10% sugar solution 20% sugar solution
10% sugar solution 20% sugar solution
15% sugar solution 15% sugar solution
This beaker is divided with a semipermeable
membrane. The left side contains a 10% sugar
solution. The right side contains an equal amount
of a 20% sugar solution.
The different concentrations of the two solutions
cause osmotic pressure to build up on the left
side of the semipermeable membrane. This
pressure forces water through the membrane
from the solution with the lower concentration
toward the solution with the higher concentration.
When the solute concentrations are the same,
water will stop moving through the membrane.
water
sugar
molecules
semipermeable
membrane
Goodheart-Willcox Publisher
23-7 Osmosis causes water to be drawn across semipermeable
membranes to equalize solute concentrations.