Small and ultra-small angle neutron scattering studies of commercial milk

Milk and milk products are an essential part of global nutrition and the world-wide food industry. Studies of milk components using scattering techniques are well documented in the literature. However, those studies focused on the $q$ scattering wavevector region ${10}^{-3}<q<2{\text{Å}}^{-1}$ . This manuscript presents scattering results in the region $3\times {10}^{-5}<q<2\times {10}^{-2}{\text{Å}}^{-1}$ , a region that allows the simultaneous study of fat globules and proteins found in commercial food-grade milk. The small and ultra-small angle neutron scattering (SANS and USANS) measurements show that a model based on the Schulz distribution function using uniform spheres was a reasonable choice to successfully fit the scattering features below $q=0.007{\text{Å}}^{-1}$ . Contrast measurements using D₂O on whole milk were carried out to distinguish fat from protein signals. Casein micelles were found to have mean diameters of 96 ± 10 nm with 33% polydispersity. The average scattering length density of the micelles varied from -0.04 × 10^-6 _Å ^-2 in homogenized, pasteurized commercial milk to 2.8 ×10^-6 _Å ^-2 with 50% dilution by D₂O, with a match point of 43 ± 3%, as seen in previous studies. It was found that the average diameter of fat globules in homogenized whole milk was $0.47\pm 0.04\text{microm}$ with a polydispersity of 45 ± 5%, and a volume fraction of 0.034 ± 0.002 when the scattering length density is fixed at 0.20 × 10^-6 _Å ^-2. These USANS measurements provide an important foundation as similar techniques are employed to study cheese varieties and cheese formation.