Electrostatic Interactions between Lactoferrin and b-Lactoglobulin in Oil-in-Water Emulsions - Food Colloids: Self-Assembly and Material Science - page 168

We recently examined the adsorption behaviour of lactoferrin in oil-in-water
emulsions at pH 3.0 and 7.0. It was shown 8 that lactoferrin, like casein and
whey proteins, is an excellent emulsifying agent. But, in contrast to the other
milk proteins, cationic emulsion droplets can be formed with lactoferrin at
neutral pH. For emulsions prepared under the same conditions, the droplet
sizes in lactoferrin-stabilized emulsions were found to be similar to those in
b-lactoglobulin-stabilized emulsions, but the surface protein coverage was higher
in lactoferrin emulsions, possibly because of its higher molecular weight. The
adsorption of lactoferrin from a binary mixture of lactoferrin + b-lactoglobulin
at pH 7.0 was affected by electrostatic interactions, leading to higher amounts of
adsorbed proteins at the droplet surface. Competitive adsorption was observed
at pH 3.0, where both proteins carry net positive charges: b-lactoglobulin was
adsorbed in preference to lactoferrin in emulsions made using low protein
concentrations ( r 1%), whereas lactoferrin appeared to be adsorbed in prefer-
ence to b-lactoglobulin in emulsions made using high protein concentrations.
The objectives of this study were to investigate further the interactions
between lactoferrin and b-lactoglobulin in oil-in-water emulsions and to explore
the possibility of making multilayered emulsions using these two proteins.
11.2 Experimental
11.2.1 Preparation of Emulsions
Protein solutions were prepared by dispersing lactoferrin (a gift from Tatua
Co-operative Dairy Company, New Zealand), b-lactoglobulin (Sigma Chem-
ical Co., St. Louis, MO, USA) or a mixture of powders of lactoferrin +
b-lactoglobulin into Milli-Q water (water purified by treatment with a Milli-Q
apparatus, Millipore, Bedford, MA, USA), and then stirring for 2 h at room
temperature. The pH of the protein solution was adjusted to 7.0 using 1 M
NaOH or 1 M HCl. Appropriate quantities of soya oil were mixed with the
protein solution to give 30 wt.% oil in the final emulsion. The mixture was then
heated to 551C and homogenized in a two-stage homogenizer (APV 2000,
Copenhagen, Denmark) at a first-stage pressure of 250 bar and a second-stage
pressure of 40 bar. The emulsions were homogenized twice for more effective
mixing of the oil phase and stored at 201C.
In some cases, 50 g of emulsion sample prepared using 1 wt.% protein
(lactoferrin or b-lactoglobulin) was mixed with 35 g of aqueous solution
containing different concentrations of protein (lactoferrin or b-lactoglobulin)
and gently stirred for 2 h at room temperature.
11.2.2 Characterization of Emulsions
A Mastersizer MSE (Malvern Instruments, Worcestershire, UK) was used to
determine the average diameter of the emulsion droplets. The surface protein