Thermal effects on IgM-milk fat globule-mediated agglutination

Abstract

The process of agglutination causes firm cream layers in bovine milk, and a functioning agglutination mechanism is paramount to the quality of non-homogenized milks. The phenomenon is not well-described, but it is believed to occur due to interactions between immunoglobulins (Ig) and milk fat globules. For the first time, this paper demonstrates how the process of agglutination can be visualized using confocal laser scanning microscopy, rhodamine red and a fluoresceinisothiocynat-conjugated immunoglobulin M antibody. The method was used to illustrate the effect on agglutination of storage temperature and pasteurization temperature. Storage at 5 °C resulted in clearly visible agglutination which, however, was markedly reduced at 15 °C. Increasing storage temperature to 20 or 37 °C cancelled any detectable interaction between IgM and milk fat globules, whereby the occurrence of cold agglutination was documented. Increasing 20 s pasteurization temperatures from 69 °C to 71 °C and further to 73 °C lead to progressively higher inactivation of IgM and, hence, reduction of agglutination. Furthermore, 2-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that changes in storage temperature caused a redistribution of Ig-related proteins in milk fat globule membrane isolates. Poly-immunoglobulin G receptor was present in milk fat globule preparations stored at cold (4 °C) conditions, but absent at storage at higher temperature (25 °C). The findings provide valuable knowledge to dairy producers of non-homogenized milk in deciding the right pasteurization temperature to retain the crucial agglutination mechanism.

Impact of ultra-shear technology on quality attributes of model dairy-pea protein dispersions with different fat levels

“…The behavior of cream with a high-fat content has been attributed to the cold agglutination phenomena in which immunoglobulins adhere to fat globules and agglomerate together into large floccules at temperatures below 35 °C ( Vliet and Walstra, 1980 ; Vélez-Ruiz et al, 1997 ). The agglutination mechanism for immunoglobulin-fat complex formation could be deactivated at temperatures between 62 and 81 °C, which causes the milk fat globules to strongly interact with each other through milk fat globule membrane proteins or heat-denatured whey protein or destabilization of the casein micelles, resulting in a hard cream layer ( Hansen et al, 2019 ). In addition to temperature, the high pressure and shear during UST could enhance the interactions of fat globules.…”

Impact of industrial cream heat treatments on the protein composition of the milk fat globule membrane

“…Suggestively, this could reflect that a single pasteurization inactivate the heat-labile agglutinin mechanism, which was previously shown to correlate with flocculation of fat globules in fresh milk (Honkanen-Buzalski and Sandholm, 1981; Euber et al ., 1984; D'Incecco et al ., 2018). This is supported by a previous study from our group, where a key component of the agglutinin mechanism, immunoglobulin M, was inactivated when heated to temperatures above 69 °C for 15 s (Hansen et al ., 2018 b ). The inactivation of agglutination mechanism by a single pasteurization step thus had a stabilizing effect on the fat globules.…”

Milk Fat Globules: 2024 Updates

“…Some studies suggest that MFG FAs and TAGs may not be affected by homogenization and thermal processing, whereas others, working with bovine milk, have shown conflicting data. 28,[56][57][58] Freezing of HM may result in the loss of some fat and of the MFG structure. 1 Some FAs formed during cold storage of HM may be cytotoxic.…”