The use of sedimentation field flow fractionation and photon correlation spectroscopy in the characterization of casein micelles

Abstract

Sedimentation Field Flow Fractionation (SdFFF) was combined with Photon Correlation Spectroscopy (PCS), to characterize changes in the structure of the colloidal particles of reconstituted skim milk of diameter >50 nm (aggregates of casein and calcium phosphate known as casein micelles) with the changes in partitioning (with the addition of salt) of calcium (Ca), inorganic phosphate (Pi) and casein between the serum and colloidal phases of the milk. The number weighted particle size distributions are determined. These are well represented by a log-normal distribution. Methods are presented for estimating the relative contributions of scattering and absorbance to the SdFFF detector signal and for taking both into account when analysing SdFFF data. The values found for the effective density of the casein micelles were in good agreement with the literature and ranged from (1·06–1·08 g cm−3) according to the composition of micelles. The changes in the scattering intensity as determined by PCS correlated with the changes in the particle composition. Although the concentrations of colloidal calcium phosphate (CCP) (1·1–3·5 g/kg milk) and micellar casein (18·1–27·2 g/kg milk) varied considerably only small changes in the size distribution of particles >50 nm diameter were observed except for milk to which 30 mmol Pi+10 mmol Ca/kg milk had been added where the particle size distribution shows a swelling of the particles consistent with a lower than expected value for the particle density. These observations suggest that the micelles have the ability to both lose (depleted micelles) and accommodate (enriched micelles) more casein, calcium and inorganic phosphate in their interior, thus confirming the model of the micelles which postulates an open structure allowing freedom of movement of casein and small ions.

Casein nanoparticles as carriers for the oral delivery of folic acid

“…Casein proteins (αs1, αs2, β, and κ) exist in milk under a "micellar" form whilst displaying the appearance of spherical aggregates of around 50 to 500 nm and have also been considered as a natural nano-delivery system (Udabage, McKinnon, & Augustin, 2003;Walstra, 1999). In spite of their interest, only recently have caseinbased nanovehicles been successfully harnessed and stabilized with adequate procedures for delivering bioactives and drugs.…”

Sedimentation field-flow fractionation: Size characterization of food materials

“…Two types of milk were investigated, including cereal, i.e., corn, jobÕs tear, rice, and soy milk; and bovine milk, i.e., chocolate, and fresh full-fat milk. Thus far, size determination of cereal milk by FFF has never been reported, although some reports on size characterization of bovine milk by FFF exist (Jussila et al, 1997;Udabage et al, 1997Udabage et al, , 2003. The bovine milk was studied herein for comparison purpose only.…”

“…Sedimentation and flow FFF are the most commonly used. Applications of SdFFF for characterizing sub-micrometer size (Jussila, Yohannes, & Riekkola, 1997;Udabage, Mckinnon, & Augustin, 2003;Udabage, Sharma, Murphy, Mckinnon, & Beckett, 1997) and micrometer size (You et al, 2002) of food materials were previously reported.…”

The use of sedimentation field-flow fractionation in the size characterization of bovine milk fat globules as affected by heat treatment

“…SdFFF has been applied in the past for the characterization of food materials (Farmakis, Koliadima, & Karaiskakis, 2002;Mozersky, Farrell, & Barford, 1991;Saeseaw, Shiowatana, & Siripinyanond, 2005;Udabage, McKinnon, & Augustin, 2003;Udabage, Sharma, Murphy, McKinnon, & Beckett, 1997). Moreover, SdFFF has been employed to study the effect of heat treatment on the particle size of skim milk (de Kruif, 1998).…”