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Effects of Chemical Composition and Microstructure in Human Milk and Infant Formulas on Lipid Digestion

Infant formula (IF) is an important substitute for infants when human milk (HM) is unavailable; however, it was often observed with "insufficient fat" and showed different metabolic phenotypes, which may affect the growth and brain development of the infant. Considering that the milk fat digestion rate may affect the fat absorption and metabolism and further influence the metabolic phenotype, it is valuable to study the fat digestive behaviors of IF and HM. In the current study, we investigated the in vitro fat digestive properties of HM in comparison to four formulas (IF1, 2, 3, 4) including IFs enriched in OPO lipids (IF1 and IF3) and IFs with common mixed plant oils (IF2 and IF4). Results showed that the extent of eventual lipid hydrolysis of HM (98.9 ± 2.70%) was higher than those of IF1 and IF3 (90.4 ± 3.39 and 91.1 ± 1.67%, respectively) (p < 0.05) and IF2 and IF4 (81.9 ± 1.64 and 79.9 ± 1.05% respectively) (p < 0.01). Native fat globules and protein aggregation were observed at the end of HM gastric digestion, and the aggregates became smaller and then resolved from 60 to 120 min in intestinal digestion, while a large number of aggregates were observed in IF, which may slow the lipid digestion. The absorption differences between HM and IFs in lipid digestion need further study to elucidate the nutritional relevance to infant development and growth.