Electrostatic Interactions between Lactoferrin and b-Lactoglobulin in Oil-in-Water Emulsions - Food Colloids: Self-Assembly and Material Science - page 174

5

4.5

4

3.5

3

2.5

Lactoferrin

2

1.5

β -Lactoglobulin

1

0.5

12 3 456

0

0 0.5 1 1.5 2 2.5 3

Lactoferrin concentration (%)

Figure 6 Changes in protein surface coverage of emulsion droplets made with 30 wt.%
soya oil and 1 wt.% b -lactoglobulin (pH 7.0) as a function of lactoferrin added
into the emulsion. The inset shows SDS-PAGE patterns of adsorbed protein:
lane 1 represents b -lactoglobulin alone, and lanes 2-7 show increasing additions
of lactoferrin

SDS-PAGE analysis of the emulsion droplets indicated clearly that, with
increasing lactoferrin concentration in the emulsion, the intensity of the
b-lactoglobulin band remained essentially constant, whereas the lactoferrin
band became more intense with increasing lactoferrin concentration up to 1.25
wt.%, which is consistent with the surface protein coverage results. The particle
size and creaming stability measurements show that all emulsions were stable to
droplet aggregation, as there appeared to be no significant changes in the d 32
values or the rate of creaming with increasing lactoferrin concentration in the
emulsion (data not shown).
These combined results show that multilayered emulsions can be produced
by interactions of oppositely charged proteins at neutral pH. A primary
emulsion, containing either anionic droplets coated with b-lactoglobulin or cat-
ionic droplets coated with lactoferrin, can be produced. A secondary emulsion
can then be made by mixing either b-lactoglobulin solution or lactoferrin
solution with the primary emulsion. The amount of protein required to saturate
the droplet surface in these emulsion systems can be estimated, as described by
McClements: 11

C sat ¼ 3 f G sat /r 32 . (1)

Here, f is the volume fraction of the oil, r 32 the volume-surface mean radius of
the droplets, G sat the surface protein coverage at saturation and C sat the
minimum concentration of protein in the whole system that is required to
saturate the surfaces. Equation (1) is based on the assumption that, below the
saturation concentration (C o C sat ), all of the protein added to the system is
adsorbed to the droplet surfaces. Based on this assumption, a minimum