Human Milk Fat Globules from Different Stages of Lactation: A Lipid Composition Analysis and Microstructure Characterization

Abstract

The physicochemical properties of human milk fat globules (MFG) at different lactation stages from Danish mothers and the microstructure changes of MFG membrane (MFGM) at varied temperatures were investigated, and the relationship between chemical composition and the microstructure of MFGM was elucidated. The fat content in MFG was found to be significantly increased as lactation progressed, and colostrum MFG had the largest mean diameter of 5.75 ± 0.81 μm and the lowest ζ potential of -5.60 ± 0.12 mV. Chemical composition analyses of MFG revealed the following: (i) Colostrum milk fat constituted higher content in PUFAs (ω-6, and long-chain ω-6 and ω-3) than transitional and mature milk fats, with the corresponding lower content of SFA in its sn-2 position. (ii) The content of polar lipids among total lipids varied during lactation course (maximized at transitional stage); however, in terms of subclasses of polar lipids, no significant change of the relative content of sphingomyelin was observed, while the content of phosphatidycholine in mature milk was higher than that in colostrum and transitional milk. (iii) Inspection of fatty acid composition in phospholipids from different lactation milk revealed no remarkable and regular changes could be generalized; and no obvious difference of the morphologies of MFGM at different lactation stages can be visualized. An investigation of the microstructure change of MFGM vs temperature demonstrated that the segregated domains became larger as temperature decreased to 4 °C, while it became smaller when increased to 37 °C. This phenomenon indicated that, in addition to sphingimyelin and cholesterol, phospholipids might also contribute to increasing the segregated domains at lower temperature, while, at elevated temperature, these domains could be diminished, most likely due to a restructuring or distributing of sphingimyelin and cholesterol.

The relationship between size and lipid composition of the bovine milk fat globule is modulated by lactation stage

“…In dairy farm animals like goats and cows, lactation stage is closely associated with energy balance, which is reflected in a higher concentration of long-chain fatty acids in milk produced in early compared with late lactation (Griinari, McGuire, Dwyer, Bauman, & Palmquist, 1997;Kinsella, 1973;Kinsella & McCarthy, 1968;Carriquiry et al, 2009;Duchacek, Vacek, Stadnik, Beran, & Okrouhla, 2012;Strzalkowska et al, 2009). Lactation stage was also shown to associate with decreased polar lipid concentration and altered composition (Bitman & Wood, 1990;Zou et al, 2012), and increased mean MFG diameter and decreased size distribution between mature and transition milk (Zou et al, 2012). Therefore, it is well established that lactation stage is associated with (1) changes in composition and concentration of fatty acids and phospholipids and (2) changes in the mean diameter of MFG.…”

The temperature-dependent physical state of polar lipids and their miscibility impact the topography and mechanical properties of bilayer models of the milk fat globule membrane

“…High-Tm with a main phase transition at Tm = 36.4°C [8]. Using confocal laser scanning microscopy, lipid microdomains were observed in the external bilayer of the MFGM at the surface of native milk fat globules [9][10][11][12][13][14]. 37°C, and that their morphology is affected by temperature [11,13,14].…”

Towards infant formula biomimetic of human milk structure and digestive behaviour

“…As a result, most commercial IF based on blends of vegetable fats present a TG structure that differs largely from the one of HM fat (Kurvinen et al, 2002). The regiodistribution of the FA on TG affects the FA lipolysis and its subsequent uptake (Bourlieu et al, 2009;Zou et al, 2012), as digestive lipases are also regio-or stereoselective. For instance, MCFA (C8:0 to C12:0) are mainly esterified in sn-3 position in HM, and thus selectively released by the sn-3 stereospecific human gastric lipase (HGL).…”

“…Regarding the structure of HM lipids emulsion and its evolution with delivery term (Simonin et al, 1984) or lactation stages, very limited data is available (Michalski et al, 2005b;Zou et al, 2012). Michalski et al (2005b) reported an higher amount of large fat globules in early colostrum with a mode of 8.9 mm at 12 h post-partum and which decreased rapidly to 2.8 mm at 96 h post-partum (Fig.…”

“…Understanding the higher levels of organization of human MFGM or MFG has been delayed until the development of modern biophysical tools (among which confocal laser scanning microscopy). And yet, despite these developments and the obvious nutritional importance of HM, data on HM lipid structure remains limited (Simonin et al, 1984;Michalski et al, 2005b;Zou et al, 2012;de Oliveira et al, 2015de Oliveira et al, , 2016de Oliveira et al, , 2017. Many structural characteristics of HM MFG have been inferred from cow's MFG which paradoxically has been more studied.…”