The original Martha of the study is no more, but her daughter of the same name is shown on the de Kruif family farm in The Netherlands.
a cow placidly grazing in a field in The Netherlands, became an
important collaborator with researchers who successfully analyzed and
characterized the internal protein structure and the composite particles
of her milk using small-angle neutron scattering at Oak Ridge National
Laboratory’s High Flux Isotope Reactor (HFIR).
micelles, a family of related phosphorus-containing proteins, make up
80% of the protein in cow milk. They are the building blocks of dairy
products such as yogurt and cheese, supplying amino acids, calcium, and
phosphorus to the body. More important, they are the principal vehicle
for delivering calcium phosphate to rapidly growing newborns.
have long struggled with the challenge of unraveling the internal
structure of this protein. An international collaboration was formed
among University of Utrecht researchers C. G. (Kees) de Kruif and Andrei
Petukhov; Volker Urban, an instrument scientist at HFIR; and Thom
Huppertz from NIZO, a Dutch independent contract research company that
helps food and ingredient companies improve the quality and
profitability of their products.
researchers used the HFIR’s general purpose small-angle neutron
scattering instrument (GP-SANS) to study samples of milk from Martha, a
cow on the de Kruif family’s farm. They compared the neutron scattering
data with various theoretical models of casein structure that have been
proposed in the literature. The results showed that one model prevails:
The casein micelle proteins are composed of a protein matrix in which
calcium phosphate nanoclusters (about 300 per casein micelle) are
scattering also revealed that the protein’s matrix has fluctuations in
density that are attributable to the hydrophobic (water-repelling)
interactions of the casein proteins.
researchers collected critical parameters for their experiments by
first measuring the properties of casein micelles of individual cows to
obtain data for size, size distribution, protein composition, density,
and water content, which served as input.
neutron contrast variation is the tool of choice to solve the problem,”
explained de Kruif, “because one can calculate the scattering intensity
with no ambiguity.”
needed a SANS instrument for two reasons. The length scale involved is
from a few tenths of a nanometer to a few hundred nanometers. Only
neutrons can do such an in situ contrast variation for testing the
the casein micelle models show a distribution of mass within each
particle. Given the parameters determined independently, one can
calculate the neutron scattering intensity. Only if a model proposes the
correct distribution of matter can one calculate all the scattering
used the casein micelles of a single cow (Martha) because the micelles
were somewhat smaller than average and less poly-disperse. This further
limits the freedom of the parameters. We showed that these samples were
representative for the whole milk,” he said.
work may have application one day in other areas. “Casein micelles can
be used as delivery vehicles for various compounds, such as vitamins and
minerals. Knowing the internal structure will be useful in developing
such applications,” de Kruif said.
team has since applied for additional beam time to study the initial
stages of yogurt and cheese making, both a specialty of The Netherlands.
research was funded by the U.S. Department of Energy (DOE) Office of
Biological and Environmental Research, the DOE Scientific User
Facilities Division, Utrecht University, The Netherlands, and NIZO food