Impact of pasteurization and homogenization on the digestion of human milk: an in vivo study in the preterm infant

Ensuring adequate growth of preterm newborns remains a challenge. When breastfeeding is not possible, pasteurized human milk (PHM) from milk banks is preferentially administered to hospitalized newborns. Holder pasteurization (62.5°; 30 min) is applied for sanitary reasons but may reduce fat absorption through the inactivation of milk endogenous lipases. It has been suggested that homogenization of Holder-pasteurized human milk (PHM) could improve fat absorption and weight gain. The objective of the present work was to determine the impact of pasteurization and homogenization on gastric digestion in preterm infants.In a randomized controlled trial (NCT02112331), hospitalized tube-fed preterm infants were their own control to compare the gastric digestion of either i) raw (RHM) and pasteurized human milk (PHM), or ii) pasteurized (PHM) and homogenized PHM (PHHM). Over a six-day sequence, gastric aspirates were collected twice a day, before and 35, 60 or 90 min after the start of milk ingestion. The impact of homogenization on PHM digestive kinetics, lipolytic activity and disintegration was monitored. Pasteurization and homogenization affected milk initial structure, with the formation of protein aggregates at the interface of the milk fat globules in PHM and a six-fold increase of the specific surface (P<0.01) of lipid droplets in PHHM. Treatments also affected gastric aggregation. Despite inactivation of bile salt stimulated lipase, pasteurization did not impact gastric lipolysis level averaging 12.6 ± 4.7% at 90 min. Conversely, homogenization increased this level (P<0.01). Homogenization also reduced meal emptying rate (P<0.001). Pre-lipolysis occurred prior to pasteurization in all milks ranging between 2.2-4.0%. The global gastric lipolytic activity detected in fasted state averaged 17.5±2.9 U/mL/kg at pH 4.5. Postprandial lipolytic activity increased with time and was higher after administration of RHM compared to PHM (n=5) whereas it was not different after administration of PHM vs. PHHM (n=4). Overall, in vivo data gathered here are crucial for a better understanding of milk neonatal digestion and help supporting the nutritional management of preterm infants.