2. Universidad Cardenal Herrera-CEU

Objective: Lyophilization appears to be a viable method for storing human milk, assuring no microbiological contamination and preserving its health benefits and antibacterial properties. The aim of the study is to evaluate and compare the effects of different storage methods (lyophilization and freezing at −20°C and −80°C) and maternal factors (gestational length or time postpartum) upon the microbiological contents and bactericidal activity of human milk. The possible relation between bactericidal activity and the content of certain nutrients and functional components is also investigated. Methods: Microbiological content, bactericidal activity, sialic acid, and ganglioside contents, as well as protein, fat, and lactose concentrations were assessed in 125 human milk samples from 65 healthy donors in the Human Milk Bank of La Fe (Valencia, Spain). Results: Lyophilization and storage at −80°C significantly reduced the content of mesophilic aerobic microorganisms and Staphylococcus epidermidis when compared with storage at −20°C. Bactericidal activity was not significantly modified by lyophilization when compared with freezing at either −20°C or −80°C. Bactericidal activity was not correlated with fat, protein, or lactose content, but was significantly correlated to ganglioside content. The bactericidal activity was significantly greater (P < 0.05) in mature milk and in milk from women with term delivery than in milk from early lactation (days 1–7 postpartum) and milk from women with preterm delivery, respectively. Conclusions: Lyophilization and storage at −80°C of human milk yields similar results and are superior to storage at −20C with regard to microbial and bactericidal capacities, being a feasible alternative for human milk banks.

Milk supplied to neonates in neonatal units is kept at room temperature for some time, which could influence microbial growth. This study aims to evaluate the growth of Escherichia coli in HM and PIF under various treatments and conditions, as well as to determine the influence of different thawing methods on microbial growth in HM. The number of E. coli generations appearing over a 4 h period at 22 °C in HM (frozen; frozen and pasteurized; and frozen, pasteurized, and fortified) and in PIF (four brands) was determined. E. coli counts in HM inoculated and thawed using different methods were also compared. In frozen HM and in pasteurized and frozen HM, significant differences were found after 2.5 h and 1.5 h, respectively. In PIF, differences were found between 1.5 and 3 h. With regard to the thawing process, the lowest microorganism counts were obtained at 4 °C overnight; thus, it seems advisable to store milk at room temperature for a maximum of 1 h during administration in neonatal units. Thawing HM at 4 °C overnight should be the method of choice.