Food Lipids: Chemistry, Nutrition, and Biotechnology

Shrinkage and flash point are two frequently measured physical properties of
waxes. The flash point is the temperature at which a flash will occur if a small flame
is passed over the surface of the sample. In the liquid state, a molten wax shrinks
uniformly until the temperature approaches the solidification point. This property is
measured as the percentage shrinkage of the volume.
2. Chemical Properties of Waxes
a. Acid Value. The acid value is the number of milligrams of potassium hydroxide
required to neutralize a gram of the wax. It is determined by the titration of the
wax solution in ethanol–toluene with 0.5 M potassium hydroxide. Phenolphthalein
is normally used as the titration indicator.
Acid value =
Vw � 56.104
w
where V w is the number of milliliters (mL) of potassium hydroxide used in the
titration and w is the mass of wax.
b. Saponification Number. The saponification number is the number of milligrams
of potassium hydroxide required to hydrolyze 1 g of wax:
Saponification number =
(Vb � V w)
� 56.105
w
where w is the weight of wax sample(s), Vb the volume (mL) of hydrochloric acid
used in the blank, and Vw the volume (mL) of hydrochloric acid used in the actual
analysis. The wax (2 g) is dissolved in hot toluene (910 mL). Alcoholic potassium
hydroxide (25 mL of 0.5 M KOH) is added, and the solution is refluxed for 2 hours.
A few drops of phenolphthalein are added and the residual potassium hydroxide is
titrated with 0.5 M hydrochloric acid. A blank titration is also performed with 25
mL of 0.5 M alcoholic potassium hydroxide plus toluene.
c. Ester Value. Ester value, the difference between the saponification number and
the acid value, shows the amount of potassium hydroxide consumed in the saponification
of the esters.
d. Iodine Number. The iodine number expresses the amount of iodine that is
absorbed by the wax. It is a measure of the degree of unsaturation.
e. Acetyl Number. The acetyl number indicates the milligrams of potassium hydroxide
required for the saponification of the acetyl group assimilated in 1gofwax
on acetylation. The difference of this number and the ester value reflects the amount
of free hydroxy groups (or alcohol composition) in a wax. The wax sample is first
acetylated by acetic anhydride. A certain amount of acetylated wax (about 2 g) is
taken out to be saponified with the standard procedure in the measurement of the
saponification number. The acetyl number is the saponification number of the acetylated
wax.
3. Properties of Important Naturally Occurring Waxes
a. Beeswax. Beeswax is a hard amorphous solid, usually light yellow to amber
depending on the source and manufacturing process. It has a high solubility in warm
benzene, toluene, chloroform, and other polar organic solvents. Typically, beeswax
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.