Changes in bioactive proteins and serum proteome of human milk under different frozen storage

Natural Association of Lysozyme and Casein Micelles in Human Milk

“…The lower in vitro specific enzymatic activity of lysozyme in the supernatant compared to the casein micelles or the hrLYZ could be due to the lower stability of lysozyme in the supernatant or result from an increase in activity after binding to the caseins. Encapsulation could contribute to the protection of the lysozyme molecule, thus avoiding a decrease in activity due to storage or preparation. , The present study is not suitable to conclusively evaluate this phenomenon. Therefore, the effect of the association of hrLYZ and isolated human caseins is still under investigation.…”

“…Other reasons could be the sample handling prior to analysis or the different stages of lactation, as the lysozyme content increases during time postpartum. ,, Akinbi et al and Chang et al showed that freezing human milk samples at −20 °C can lower the concentration and the enzymatic activity of lysozyme. Qu et al also found a decrease in lysozyme concentration in human milk after storage at −18 °C for 60 or 180 days determined by enzyme-linked immunosorbent assay (ELISA). On the other hand, they reported an increase in the abundance of lysozyme peptides, which indicates that lysozyme concentration did not decrease but lost some of its bioactivity.…”

“…They concluded that lysozyme and other whey proteins are trapped to a nonspecified amount in the casein micelle but also mentioned that this effect can be the result of a coprecipitation of whey proteins during the acid treatment. Another indication of the binding of lysozyme to casein micelles in the human milk system is the increase of lysozyme content in human milk serum obtained by ultracentrifugation at 100,000 g after storage at −18 °C for 60 or 180 days observed by Qu et al The authors attributed this result to the release of casein-bound lysozyme in the milk serum following cold treatment as a result of a decrease of the pH value.…”

“…Lysozyme can also be detected in the precipitate together with caseins . Also, the effect that the lysozyme concentration in the whey protein fraction measured after ultracentrifugation increases during storage of human milk at −18 °C is attributed to a release of bounded lysozyme from casein micelles …”

“…20 Also, the effect that the lysozyme concentration in the whey protein fraction measured after ultracentrifugation increases during storage of human milk at −18 °C is attributed to a release of bounded lysozyme from casein micelles. 21 The objective of this study was to investigate whether and to which extent lysozyme is bound to casein micelles in human milk and to determine the ratio of casein micelle-bound to unbound lysozyme to get a better insight into the nanostructured composition of this complex biofluid. Therefore, we analyzed the lysozyme content of human milk obtained from 10 healthy mothers before and after ultracentrifugation with high-performance liquid chromatography with detection in the ultraviolet range and mass spectrometry (reversed-phase highperformance liquid chromatography-ultraviolet electrospray ionization-quadrupole time-of-flight mass spectrometry (RP-HPLC-UV-ESI-Q-TOF)).…”