Milk homogenization monitoring: Fat globule size estimation from scattering spectra of milk

The fat globule size distribution of raw milk and milk with an increasing degree of homogenization was estimated based on their bulk light scattering properties in the Vis/NIR wavelength range. The particle size distribution (PSD) was approximated as a lognormal distribution, of which the parameters were estimated simultaneously with the fat concentration. This resulted in a good agreement between the estimated PSDs and the reference PSDs obtained by laser diffraction in case of raw and strongly homogenized samples. The accuracy increased if a known fat concentration was incorporated, or when the scattering coefficient and anisotropy factor spectra were used simultaneously as input. For mildly homogenized samples, the lognormal distribution was unable to fit the bimodal PSD correctly and focused on the largest fat globules. In this case, the estimated PSDs provided still relatively accurate information on D90, D32 and the right distribution tail, which contains the largest fat globules. Industrial relevance: The presented estimation method demonstrates the potential of bulk scattering spectra for determining the PSD and concentration of scattering particles in turbid media. Further development of this technology can lead to new solutions for spectroscopic PSD determination, allowing on-line monitoring systems for a wide range of food and non-food products.