Thawing rate and heating temperature effects on immunoglobulin A and lysozyme activity in human milk

BackgroundThe rate of infants receiving frozen HM is increasing, allowing critically ill preterm infants and infants with working mothers to benefit from the advantages of their mother's milk. The effects of thawing and warming on secretory immunoglobulin A (SIgA) and lysozyme activity in frozen human milk (HM) should be investigated to identify optimal methods for preserving immune factors in frozen HM.MethodsForty mothers that delivered full-term infants provided milk that was frozen and stored at -18°C two months before analyses. We compared the methods involving placing the container in a 4°C refrigerator overnight (slow thawing, ST) and placing it in a container of warm water (rapid thawing, RT). Additionally, we investigated the effect of warming temperature using room temperature (25°C) and physiological temperature (37°C). SIgA concentrations and lysozyme activities in the milk samples were determined by ELISA kits and fluorometric lysozyme activity assay kits, respectively. Data were analyzed by paired t-tests.ResultsSIgA concentrations and lysozyme activity were reduced by 16.5-52.1% and 16.8-39.3% in frozen HM compared to fresh HM, respectively. Significantly higher SIgA concentrations were maintained with slow thawing and warming at 37°C than with rapid thawing and warming at 25°C (p <0.001). Greater lysozyme activity was retained at 25°C with slow thawing than with rapid thawing (p <0.001) and more was preserved at 25°C than at 37°C with slow thawing (p <0.01).ConclusionsThawing HM overnight in the refrigerator before warming has the potential to preserve SIgA levels and lysozyme activity better than thawing immediately after removal from the freezer. Broader temperatures ranges should be analyzed to determine the temperature that minimizes HM SIgA and lysozyme activity losses.Trial registrationNot applicable