CaSEIN MICELLES aS NaNOCapSULES
Iron deficiency anaemia is a problem in both developing and
developed countries. Iron is notoriously difficult to deliver in
food systems because of reactivity and solubility problems. Free
iron catalyzes lipid oxidation and rancidity in foods, and iron
chelated with casein proteins from milk is thus an attractive
alternative. Casein-chelated iron has been used in the past to
fortify dairy foods with up to 1.5 mM of iron, but a new technology has increased fortification capacity by more than 10-fold.
Caseins comprise 80% w/w of milk protein, and they are
present in milk as colloidal micelles a few hundred nanometres in diameter. Casein micelles are nature’s vehicle for delivering highly digestible protein to the bovine infant, but they
also contain nanoclusters of calcium phosphate, thus delivering
calcium in a stable and soluble form.
In the new process, developed at the Riddet Institute in
New Zealand, milk is first partially depleted of calcium by exposing it to an ion-exchange resin at low temperature. With high
levels of calcium depletion the casein micelles dissociate, and
the milk becomes translucent (Fig. 1, page 117).
With 70% calcium depletion, up to 20 mM of added iron
will bind to milk proteins in a soluble form that is stable during
heat processing ( 90 ˚C for 30 min). The process has been patented and commercialized under the brand FerriPro. Formulation trials have shown that a chocolate milk fortified with
FerriPro can deliver 50% of a child’s recommended daily intake
(RDI) of iron in a single 200 mL serving.
Similarly, researchers at the University of Guelph in
Ontario, Canada, have found that partially removing beta-casein
from micelles can enhance the binding of other bioactive molecules. Up to 60% depletion of the beta-casein is achieved by
holding a suspension of micelles at 4 ˚C followed by centrifugal
separation. Depletion apparently makes more space for ligands
to diffuse into micelles and bind to the proteins, as indicated by
stronger binding of both resveratrol (a polar antioxidant found
in red wine) and curcumin (a nonpolar anti-tumour agent found
Oil-in-water emulsions are dispersions of lipid droplets in water.
They are inherently unstable, and to inhibit phase separation an
amphiphilic emulsifying agent (i.e., a molecule with both polar
and nonpolar regions) is needed. Solid particles adsorb strongly
to interfaces and provide better steric stabilisation than small
molecule emulsifiers. Particle-stabilized or “Pickering” emulsions are an area of active research.
Riddet Institute scientists have developed a new type of
particle-stabilized emulsion that can be made with food-safe
materials. This system uses a protein-stabilized nanoemulsion
(shell lipid) as the emulsifying agent to disperse a second lipid
(core lipid). This results in a nested structure as shown in Fig.
2. The system for creating the structure has been named NanoEmulsion Shell Technology, or NEST.
Antioxidants are traditionally incorporated into oil-in-water emulsions by dissolving them in the core lipids, resulting in a homogeneous concentration within oil droplets. This is
a rather inefficient use of antioxidants, which are most needed
at the oil-water interface, where exposure to dissolved oxygen
and metal ions occurs. The patented NEST emulsion structure
allows for the dispersal of antioxidants in the shell lipid, thus
concentrating them where they are most needed. Even without
antioxidants, the NEST structure appears to inhibit oxidation
more effectively than traditional emulsions (Fig. 3).
WHEY pROTEIN aRMOUR
β-Lactoglobulin (β-lg) is the major protein in the whey fraction
of bovine milk. Its folded 3-dimensional structure creates two
sites for specific binding of long-chain hydrophobic molecules,
including vitamin A and vitamin D (Fig. 4). Recent research has
examined whether this vitamin-binding ability can be used to
protect and deliver vitamins in health-enhancing foods.
Taiwanese researchers recently tested the bioavailability of
vitamin D in mice that were fed the vitamin alone or with milk,
whey protein, casein or β-lg. Casein produced no improvement
FIG. 2. Left: schematic structure of NEST emulsions; center: confocal scanning laser microscope images of a NEST emulsion
droplet showing lipid (red) and protein (green); right: transmission electron micrograph of the surface of a NEST droplet.
From Ye et al., 2013. Reprinted with permission from Ye, A., X. Zhu, and H. Singh, Oil-in-water emulsion system stabilized
by protein-coated nanoemulsion droplets, Langmuir 29: 14403–14410. Copyright 2013 American Chemical Society.