The effect of freeze-drying and storage on lysozyme activity, lactoferrin content, superoxide dismutase activity, total antioxidant capacity and fatty acid profile of freeze-dried human milk

Abstract

Pooled human milk samples were freeze-dried and stored for 6 weeks at a temperature of 5 °C and 25 °C. Freeze-drying decreased the water content of milk by 86.5%, and the obtained lyophilizate was readily soluble in water. The freeze-drying process did not affect superoxide dismutase (SOD) activity, fatty acid (FA) profile or lactoferrin (LF) content, but it decreased total antioxidant capacity (TAC) of human milk by 22.1% and induced a minor increase in lysozyme (LZ) activity, by approximately 9.8%. Storage of freeze-dried milk did not show significant influence on TAC, LF, FA and LZ levels, while after six weeks of storage SOD activity decreased by around 27% relative to the level noted immediately after lyophilization. These findings and the remaining state of knowledge imply, that freeze-drying can be a useful method of human milk storage.

Highlights

• Lyophilization does not significantly affect the level of SOD and LF of human milk.

• In freeze-dried milk, bioactive substances: TAC level, LF, FA and LZ, remain stable even at room temperature.

• During storage of freeze-dried milk SOD activity decreases significantly.

Keywords:

• Human milk
• freeze-drying
• total antioxidant capacity
• enzymes
• fatty acids

Acknowledgments

The authors would like to thank the mothers for their time and effort in providing milk samples.

Declarations of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Ethical statements

The authors declare that they do not have any conflict of interest. Written informed consent was obtained from all study participants. All experimental procedures have been approved by the Local Ethics Committee of the Medical University of Gdansk. The subjects gave their informed consent before the start of any procedure.

Additional information

Funding

The project was funded by a grant from the National Science Center, allocated pursuant to decision No. DEC-2013/09/B/NZ9/01779.