Possibility of Microwave Thawing of Human Milk: Effects on Milk Composition and Temperature Distribution

Freezing is commonly used to preserve human milk; however, microwave thawing is not recommended due to nutritional loss and creation of hotspots in the milk. Data on compositional changes after microwave thawing and uneven temperature distribution are scarce.

To investigate the association between microwave heating and the composition and temperature distribution of human milk.

In this laboratory-based cross-sectional experimental study, 35 milk samples were divided into six groups based on preheating operations and milk bag material (35 samples each). After thawing at 600 watts for 30 seconds, temperature was immediately measured using thermography. Uneven temperature distribution was evaluated by the difference between maximum and minimum temperatures. Subsequently, it was mixed by inverting, and the temperature was measured again. The secretory Immunoglobulin A and lactoferrin concentrations were analyzed using enzyme-linked immunosorbent assays. Macronutrients were analyzed using mid-infrared transmission spectroscopy. Results were compared with thawing in running water to explore the feasibility of microwave thawing.

The median temperature in the sonicated group (33.6 °C) was significantly decreased compared to that in the untreated group (54.9 °C). The median temperature in the polyethylene bag group (42.0 °C) was also significantly decreased compared to that in the polypropylene bag group (53.2 °C). The temperature after inversion mixing was close to the recommended temperature for feeding. The median concentration significantly decreased for secretory Immunoglobulin A (0.9-16.6%) and lactoferrin (21.3-29.1%) after microwaving.

Component losses caused by microwave thawing were not clinically problematic compared to the standard value and could be minimized. Microwave heating may be an option for thawing human milk.