Food Lipids: Chemistry, Nutrition, and Biotechnology

HLB=7� � (hydrophilic group numbers)
� � (lipophilic group numbers) (1)
As indicated in Table 1 [18], group numbers have been assigned to hydrophilic
and lipophilic groups of many types. The sums of the group numbers of all the
lipophilic groups and of all the hydrophilic groups are substituted into Eq. (1) and
the HLB number is calculated. The semiempirical equation above has been found to
have a firm thermodynamic basis, with the sums corresponding to the free energy
changes in the hydrophilic and lipophilic parts of the molecule when micelles are
formed.
The HLB number of an emulsifier gives a useful indication of its solubility in
the oil and/or water phases, and it can be used to predict the type of emulsion that
will be formed. An emulsifier with a low HLB number (4–6) is predominantly
hydrophobic, dissolves preferentially in oil, stabilizes water-in-oil emulsions, and
forms reversed micelles in oil. An emulsifier with a high HLB number (8–18) is
predominantly hydrophilic, dissolves preferentially in water, stabilizes oil-in-water
emulsions, and forms micelles in water. An emulsifier with an intermediate HLB
number (6–8) has no particular preference for either oil or water. Nonionic molecules
with HLB numbers below 4 and above 18 are less surface active and are therefore
less likely to preferentially accumulate at an oil–water interface.
Emulsion droplets are particularly prone to coalescence when they are stabilized
by emulsifiers that have extreme or intermediate HLB numbers. At very high
or very low HLB numbers, a nonionic emulsifier has such a low surface activity that
it does not accumulate appreciably at the droplet surface and therefore does not
provide protection against coalescence. At intermediate HLB numbers (6–8), emulsions
are unstable to coalescence because the interfacial tension is so low that very
little energy is required to disrupt the membrane. Maximum stability of emulsions
is obtained for oil-in-water emulsions using an emulsifier with a HLB number around
10–12, and for water-in-oil emulsions around 3–5. This is because the emulsifiers
are sufficiently surface-active but do not lower the interfacial tension so much that
the droplets are easily disrupted. It is possible to adjust the effective HLB number
by using a combination of two or more emulsifiers with different HLB numbers.
One of the major drawbacks of the HLB concept is its failure to account for
the significant alterations in the functional properties of an emulsifier molecule that
result from changes in temperature or solution conditions, even though the chemical
Table 1 Selected HLB Group Numbers
Hydrophilic group
—SO 4NA �
—COO � H �
Tertiary amine
Sorbitan ring
—COOH
—O—
Source: Adopted from Ref. 18.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.
Group
number
38.7
21.2
9.4
6.8
2.1
1.3
Lipophilic
group
—CH—
—CH 2 —
—CH 3
Group
number
0.475
0.475
0.475