http://www.ext.colostate.edu/pubs/CO.../nn030929.html
"Apples produce their own natural wax coating during growth. This helps
them retain moisture after picking. However, many packers wash picked
apples with a solvent detergent to remove dirt and pesticide residues
that accumulate during growth. This also removes the apple's natural
wax coating, leaving the apple susceptible to loss of moisture and
eating quality.

To retard this chain of events, many packers coat washed apples with a
commercial wax such as Carnauba. Carnauba is an inert product derived
from the leaves and buds of the Brazilian wax palm. It's been used in
foods since 1900 and, according to FDA's Division of Toxicology, causes
no ill effects at levels used."

http://www.bestapples.com/facts/waxing.html
"Whether natural or applied, wax may whiten on the surface of fruits or
vegetables if they have been subjected to excessive heat and/or
excessive moisture. This whitening or chalky appearance is similar to
that of a candy bar when you place it in the freezer.

Research has shown that apple waxing prevents moisture loss, enhances
firmness retention and slows down the apple respiration rate.

In the most recent study conducted at the U.S. Department of
Agriculture's Agricultural Research Service Laboratory in Wenatchee,
Wash., Red Delicious apples from Controlled Atmosphere (CA) storage
were held at room temperature for eight days (duplicating how apples
are treated in grocery stores). The unwaxed apples lost firmness faster
than the waxed apples.

A second study showed the waxed apples also had less weight loss after
eight days at room temperature. Research horticulturists from the USDA
report "the use of wax on Red Delicious apples improved firmness and
color, and reduced weight loss."