The effect of storage at 25 °C on proteins in human milk

Comparison of Effects of Storage at Different Temperatures in a Refrigerator, Upright Freezer on Top of Refrigerator, and Deep Freezer on the Immunoglobulin A Concentration and Lysozyme Activity of Human Milk

This study aimed to investigate the effects of storing expressed human milk (HM) at different domestic storage temperatures on the secretory immunoglobulin A (SIgA) concentration and lysozyme activity. Forty mothers of full-term infants aged one to six months provided milk samples. The fresh samples were examined within 24 h of expression, and the other samples were stored in a refrigerator for four days or in two types of freezers for six months. The SIgA concentrations and lysozyme activity in the milk samples were studied using enzyme-linked immunosorbent assay (ELISA) kits and fluorometric lysozyme activity assay kits, respectively. The pairwise comparisons of the SIgA concentration and lysozyme activity were carried out using one-way analysis of variance with Dunnett T3 or Kruskal-Wallis tests with Bonferroni correction, depending on the data distribution. The mean temperatures of the refrigerator, upright freezer on top of the refrigerator, and deep freezer (chest freezer) were 2.0, -16.7, and -22.3 °C, respectively. Our study results highlight that the SIgA concentration and lysozyme activity of HM stored in the refrigerator for four days and in freezers for six months were significantly lower than those of fresh HM (p < 0.001). During the first six months of storage in both types of freezers, the SIgA levels were stable, whereas the lysozyme activity significantly decreased (p < 0.001). HM stored in the deep freezer had a higher SIgA concentration and lysozyme activity than HM stored in the upright freezer on top of the refrigerator. Our data support the superiority of fresh human milk over stored HM. If HM is to be stored, then storage in a deep freezer is potentially a more effective method for the preservation of SIgA concentrations and lysozyme activity than storage by refrigeration for four days or in an upright freezer on top of a refrigerator for six months.

Proof-of-concept on the effect of human milk storage time: Lipid degradation and spectroscopic characterization using portable near-infrared spectrometer and chemometrics

Human milk (HM) modifications over time represent an important issue. This work proposed to evaluate the changes in HM during one-year storage through total lipids (TL) degradation and portable near-infrared (NIR) spectrometer combined with chemometrics. Colostrum, transition, and mature stages were obtained from donors and considered in the raw and pasteurized forms. Principal component analysis in TL content showed changes in the mature stages for both forms after 75 days. Multivariate curve resolution with alternating least squares in NIR spectral data reveals a decrease in protein and triacylglycerol contents while an increase in free fatty acids (palmitic acid) contents were observed through the storage after around 5-6 months. Therefore, more than 5-6 months of storage suggest possible biochemical changes in the HM nutritional composition. Moreover, the chemometrics investigation was crucial in extracting information, bringing coherent results, and helping to understand the chemical changes in human milk during storage.

Storage of Unfed and Leftover Mothers' Own Milk

OBJECTIVE

The objective was to examine the bacteriological and immunological properties of freshly expressed, previously frozen, and leftover mothers' own milk during storage.

MATERIALS AND METHODS

In the first of two pilot studies, 12 mother-infant dyads participated. The milk studied included freshly expressed unfed and freshly expressed leftover milk. Milk samples were stored at 24°C, 4°C, or -20°C. In the second pilot study, 11 mother-infant dyads participated. The milk studied included milk that had been previously frozen, including previously frozen leftover milk. Milk samples were stored at 24°C and 4°C. After storage in both studies, the milk was analyzed for bacteriological and immunological properties.

RESULTS

Bacteriological and immunological characteristics of freshly expressed unfed and freshly expressed leftover milk and previously frozen unfed and previously frozen leftover milk remained stable during storage at 4°C for at least 6 days. The quality of all groups of mothers' milk declined when stored at 24°C for longer than 3 hours.

CONCLUSIONS

While this study provides evidence that human milk might be safe at longer storage times, storage guidelines should not be revised until more research is performed. This study serves as a call to action for more research on the topic of human milk storage, specifically leftover human milk. The study provides information to inform future study designs on the topic of unpasteurized human milk storage. More research is needed regarding leftover human milk storage with a greater number of participants, determination of the quality of human milk, and the storage of human milk in a real-life setting.

The influence of breast milk and infant formulae hydrolysates on bacterial adhesion and Caco-2 cells functioning

The aim of the study was to determine the concentration of BCM7 in human milk and infant formulae (IF) before and after eznymatic hydrolysis, and to evaluate the effect of obtained hydrolysates on interleukin-8 (IL-8) secretion and on proliferation of enterocytes in the in vitro model (Caco-2 cells). This study evaluates also the effect of hydrolysates on the adhesion of intestinal microbiota isolated from faeces of both healthy (H) and allergic (A) infants. In the study we investigated breast milk delivered by mothers of healthy ('healthy milk'; HM) and allergic ('allergic milk'; AM) infants. Three infant formulae were investigated: from hydrolysed cow casein (IF1), from hydrolysed cow whey (IF2) and from whole cow milk (IF3). Intestinal bacteria: Bifidobacterium, lactic acid bacteria, Enterobacteriaceae, Clostridium and Enterococcus were isolated from faeces of five healthy and five allergic infants. Mixtures of bacterial isolates and bacteria adhering to Caco-2 cells were characterised qualitatively with PCR-DGGE, and quantitavely with FISH. Concentration of BCM7 in breast milk and infant formulae was 1.6 to 8.9 times higher after enzymatic hydrolysis in comparison to undigested samples. The presence of this peptide resulted in alteration of intestinal epithelial proliferation and increase in secretion of IL-8. The quantitative profile of adherred bacteria applied as a mix of all isolates from healthy infants (H-MIX) was unchanged in the presence of HM hydrolysate and was modulated (increased number of beneficial Bifidobacterium and reduced commensal Enterobacteriaceae) in the presence of all IF hydrolysates. The presence of IF hydrolysates affected the profile of adhering isolates obtained from allergic infants (A-MIX) and reduced the adhesion of Enterobacteriaceae; the IF2 and IF3 hydrolysates decreased also the total number of adhering bacteria (TBN). However, a stimulating effect of AM hydrolysate on A-MIX adhesion (increased TBN) was observed.

Longitudinal analysis of protein glycosylation and β-casein phosphorylation in term and preterm human milk during the first 2 months of lactation

Human milk proteins provide term and preterm infants with both nutrition and protection. The objective of the present study was to examine longitudinal changes in the protein composition of term and preterm milk during the first 2 months of lactation, focusing on protein phosphorylation and glycosylation. Using gel electrophoresis, the relative concentration and glycosylation status of lactoferrin, secretory Ig A, β-casein, α-lactalbumin, serum albumin, bile salt-stimulated lipase, xanthine oxidoreductase, tenascin and macrophage mannose receptor 1 were measured in milk collected on days 7, 10, 14, 18, 21, 28 and 60 postpartum from preterm mothers (28-32 weeks gestation, n 17). The phosphorylation status of β-casein was also investigated. To determine if these variables differ in term and preterm milk, samples from term mothers (38-41 weeks gestation, n 8) collected on days 7, 14 and 30 of lactation were also analysed. The concentration of the abundant milk proteins decreased during lactation in term and preterm milk (P <0·05). No difference in protein glycosylation was observed, except for the glycoproteins serum albumin and tenascin. The phosphorylation of β-casein varied significantly between term and preterm milk. Further investigation is required to determine whether these modifications affect protein function and are clinically important to preterm infants.