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Chapter 23 Separation Techniques: Mechanical and Chemical Methods
To separate the components of whey, the liquid is fi rst passed
through fi lters that remove the protein molecules. At this point, the
liquid is a solution of lactose, lactic acid, and salts. A specially designed
reverse osmosis membrane is then used to remove the lactose.
Reverse osmosis is also used to make maple syrup. With a reverse
osmosis machine, 80% of the water can be removed from maple sap
without the use of heat. The remaining liquid is then heated to develop
characteristic fl avor, color, and sugar concentration for maple syrup.
See 23-9.
The Role of Semipermeable Membranes
Semipermeable membranes are used to separate many food
components. Egg whites, soy proteins, and enzymes are among the
substances separated with these
membranes.
Semipermeable membranes
are designed for the specifi c
solutes that must be trapped and/
or allowed to pass through them.
These membranes are often
designed to allow salts and acids
to pass through with the water.
This reduces the risk of high salt
or acid concentrations damaging
the solids in the concentrate. The
membranes used to concentrate
fruit juices must allow water but
not fl avor compounds to fl ow out
of the juice. Such factors as the size,
polarity, and chemical makeup
of solutes determine the type of
membrane to be used.
Sometimes a combination
of membranes is most effective.
Research has shown that deposits
of some proteins and polysac-
charides can improve the selective
nature of semipermeable
membranes. For instance, whey
protein can be deposited in a gel-
like layer on a membrane used
for apple juice. This will decrease
the fl ow of fl avor compounds
through the membrane with the
water. Therefore, the apple juice
will be concentrated without loss
of fl avor.
Janet Ward
23-9 The processing and bottling of maple syrup at Sprague’s Maple Farms
in Portville, New York is set up for public viewing. The small operation uses
a reverse osmosis machine.