Contribution of Light Scattering to near Infrared Absorption in Milk

Abstract

The presence of milk fat globule emulsion produces scattering phenomena on near infrared (NIR) radiation through the raw milk. Numerically, 80% of milk fat globules have a diameter of less than 3 µm interfering with the radiation having a wavelength from 1 µm to 2.5 µm with a radiation dispersion in all directions. Consequently, the NIR transmitted radiation does not behave in accordance with Lambert-Beer's law: the NIR spectra of milk samples with high fat content have high offset values and lower specific absorptions than those of samples with lower fat levels. Usually, this problem is reduced by acting at the level of sample preparation (homogenisation), of optical geometry (transflectance mode coupled with the use of an integrating sphere to collect the widespread radiation) and using chemometric regression models able to optimise non-linear spectral responses. Transmittance measurements have already been exploited for the determination of macro-composition in the agro-food and in the dairy fields. In this work, a set of 150 individual milk samples, collected over three days from a single farm with 49 milking cows, was analysed with Fourier transform-NIR apparatus in order to study the effects of scattering on partial least squares predictors for casein. The spectra of non-homogenised raw whole milk and the respective skimmed samples were collected in transmission mode. Using the true scattering curves obtained by subtraction from the raw milk spectra of skimmed milk spectra the extended multiplicative scatter correction (EMSC) estimate of scattering effects was optimised. EMSC uses polynomial filters in modelling the aspecific absorptions due to the scattering effects. The correct scatter elimination can help in the individuation and interpretation of the true predictors in calibration procedures.

Visible and near-infrared bulk optical properties of raw milk

“…The same phenomenon is even more clear for the other 2 groups. Additionally, in these groups, a steeper μ s spectrum in the Vis/NIR range is also related to a maximum μ s at smaller wavelengths, typical for smaller scattering particles (Cattaneo et al, 2009;Cabassi et al, 2013;Aernouts et al, 2015). Within each group of raw milk samples with a similar fat content, the μ s spectra seem to cross each other in the 1,200 to 1,400 nm wavelength range.…”

Solid‐State Thin‐Film Broadband Short‐Wave Infrared Light Emitters

“…Further, we present its application in food industry to distinguish the animal milk from vegetable‐based milk. The difference in light scattering coefficient [ 31,32 ] in the infrared range of 1100–1300 nm allows to distinguish the different types of milk (cow, almond, rice, and oat) by measuring their transmittance across the SWIR (Figure 4d).…”

Effect of homogenisation on detection of milk protein content based on NIR diffuse reflectance spectroscopy

“…In particular, when the homogenisation pressure at the first stage reached 30 MPa combined with 5 MPa at the second stage, 30/5 MPa, the fat globules were very small and distributed evenly. Several studies have reported that big fat globules cause serious scattering effect on NIR light (Cattaneo et al, 2010;Melfsen et al, 2012b). The decrease in size and the uniform distribution of fat globules would be helpful to decrease light scattering effect and to make the obtained NIR spectra have good repeatability.…”