Effects of different freeze-thaw processes on the bioactivity and digestibility of human milk

Human milk provides the best nutrition for the newborn. Nowadays, more and more women choose to collect and freeze their own milk for later use. However, there has been no consensus on freezing conditions and no standard criteria for thawing. This study aimed to evaluate the effect of different freeze-thaw processes (frozen at −18 °C and −60 °C for 30 d, followed by placing in the air at 4 °C for 10-h stationary, placing in the air at 25 °C for 1-h stationary and shaking in the tepid water at 45 °C for 1 min, respectively) on the integrity and digestion properties of human milk. The results showed that the content of fat, protein and bioactive proteins slightly changed as a result of freeze-thaw processes; however, lipase activity and digestibility of lipids and proteins changed significantly. For human milk frozen at −18 °C and thawed at 45 °C, increased initial lipolysis, fusion of human milk fat globules (HMFGs), and protein aggregation was observed, which impacted the digestion of lipids and proteins. Human milk frozen at −60 °C and thawed at 45 °C could maintain the original characteristics of HMFGs and protein to the maximum extent, which provided the digestion characteristics most similar to fresh human milk.