Optical properties of human milk

Abstract

With human milk being the most important source of infant nutrition, the protection and support of breastfeeding are essential from a global health perspective. Nevertheless, relatively few objective methods are available to investigate human milk composition and lactation physiology when a mother experiences breastfeeding problems. We argue that optics and photonics offer promising opportunities for this purpose. Any research activity within this new application field starts with a thorough understanding on how light interacts with human milk. Therefore, the aim of this study was to investigate the full set of optical properties for human milk and the biological variability therein. Using a novel approach that combines spatially resolved diffuse reflectance spectroscopy (SR-DRS) and spectroscopic optical coherence tomography (sOCT) between 450 and 650 nm, we quantified the absorption coefficient µ a , scattering coefficient µ s , reduced scattering coefficient µ s ', anisotropy g and backscattering coefficient µ b,NA of mature human milk from 14 participants released at different stages during a breastfeed (foremilk, bulk milk and hindmilk). Significant correlations were found between µ a , µ s , µ s ' and µ b,NA and the biochemically determined fat concentration per sample (R s = 0.38, R s = 0.77, R s = 0.80, R s = 0.44 respectively). We explained the observed variations in the optical properties of human milk using Mie theory and the biological variability in both the concentration and size distribution of milk fat globules. In conclusion, we have provided a full set of optical properties for human milk, which can hopefully serve as a starting point for future biophotonic studies on human milk and the milk containing lactating breast.

Dependency of the optical scattering properties of human milk on casein content and common sample preparation methods

“…In the visible wavelength range, the optical attenuation by milk is dominated by the scattering of fat globules (∼0.2 to 11 μm in diameter). 6 In our recent work, we mapped the full set of optical properties of human milk and demonstrated significant correlations between milk fat concentration and the absorption coefficient μ a , scattering coefficient μ s , reduced scattering coefficient μ 0 s , and backscattering coefficient μ b;NA . 6 Samples were homogenized through gently inverting by hand, to ensure that the fat globule size distribution was not affected by the sample preparation method.…”

“…6 In our recent work, we mapped the full set of optical properties of human milk and demonstrated significant correlations between milk fat concentration and the absorption coefficient μ a , scattering coefficient μ s , reduced scattering coefficient μ 0 s , and backscattering coefficient μ b;NA . 6 Samples were homogenized through gently inverting by hand, to ensure that the fat globule size distribution was not affected by the sample preparation method. Building upon our previous work, this work aims to investigate the effect of other common and time-efficient sample preparation methods on the scattering properties of human milk: vortexing and sonication.…”

“…4 Major reasons for mothers to stop breastfeeding are pain due to breastfeeding problems and (the perception of) insufficient milk supply. 5 As we have detailed in our recent work, 6 photonics offers many valuable opportunities for the development of more objective tools for lactation science and support. These tools can be employed to obtain unique insights into the physiology of the lactating breast, [7][8][9] but also as an efficient method to quantify human milk composition.…”

“…Numerical results have previously shown that-due to their small size-casein micelles have a relatively small effect on μ s (∼6%), whereas they do notably affect μ 0 s (∼43%, depending on fat concentration). 6 Knowledge on the contribution of casein to the optical scattering properties of human milk is, therefore, relevant for both the quantification of fat content and the casein content itself.…”

“…In this work we quantified the scattering properties of human milk, by using our existing combination of spatially resolved diffuse reflectance spectroscopy (SR-DRS) and spectroscopic optical coherence tomography (sOCT). 6 Human milk samples were homogenized with four different methods: (1) gently inverting the milk samples by hand, (2) vortexing, (3) sonication for 1 min, and (4) sonication for 5 min. The contribution of casein micelles was estimated by measuring the scattering properties before and after denaturation of the casein micelles.…”