Influence of infant milk formula processing on protein digestion and gut barrier health in vitro and in vivo
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Date
2024
Authors
Dold, Cathal A.
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Publisher
University College Cork
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Abstract
Thermal treatment is essential during infant milk formula (IMF) processing to produce a safe product. However, high thermal loads during IMF processing denature native milk proteins, increase protein aggregation and promote the Maillard reaction, with the generation of advanced glycation end products. Denatured and aggregated dairy proteins will be digested differently in the infant gut compared to native dairy proteins. The degree of glycation will also alter digestion. Employing lower temperatures or non-thermal processing methods, or both, should produce IMF with a higher native protein content and less advanced glycation end products.
Previously, in our laboratory, a split-stream process using membrane filtration technology with a ceramic 1.4 µm microfiltration membrane and a 0.2 µm polyvinylidene difluoride polymeric membrane was employed to produce an IMF (MEM-IMF) with significantly higher levels of native whey protein compared to a thermally processed IMF (125 °C for 5 s) (HT-IMF).
The objective of this thesis was to examine the gastrointestinal responses of the young gut in vitro, in vivo and ex vivo to MEM-IMF. The hypothesis was that IMF produced using membrane filtration technology will increase protein digestibility in the upper gastrointestinal tract and support gut barrier health compared to HT-IMF.
Young pigs, at 28 days old, were blocked by sex, weight and litter origin and assigned to one of two treatments (n = 14 per treatment) and fed (1) a starter diet containing 35% MEM-IMF or (2) a starter diet containing 35% HT-IMF. Pigs, 28 days later, were sacrificed 180 mins after final feeding for the collection of gastric, duodenal, jejunum and ileal contents. Analysis revealed a significant increase in the degree of protein hydrolysis, release of free amino acids and an increase in water-soluble proteins and peptides in the gastrointestinal tract of young pigs fed MEM-IMF diets compared to pigs fed HT-IMF diets (P < 0.05). MEM-IMF fed pigs had a higher number of goblet cells, acidic mucus and mucin-2 protein in the jejunum compared to pigs fed HT-IMF (P < 0.05). In the duodenum, MEM-IMF fed pigs had higher trypsin activity in the gut lumen, higher mRNA transcript levels of claudin-1 in the mucosal scrapings and higher lactase activity in brush border membrane vesicles compared to those pigs fed HT-IMF (P < 0.05).
To further investigate these gut responses, in vitro gut barrier models were employed (i.e. polarised monolayers of human enterocytes (Caco-2) and goblet cells (HT29-MTX)). Ex vivo jejunal MEM-IMF and in vitro digested MEM-IMF significantly reduced the ability of pathogenic bacteria to adhere to HT29-MTX monolayers, compared to HT-IMF test samples (P < 0.05). This benefit is likely attributed to changes in mucus biomarkers. Ex-vivo jejunal MEM-IMF increased mRNA transcript levels of mucin-2 and mucin-5AC in Caco-2/HT29-MTX monolayers compared to jejunal HT-IMF (P < 0.05). In vitro digested MEM-IMF increased mucin-2 protein and mRNA transcripts of mucin-1 and mucin-2 in Caco-2/HT29-MTX monolayers compared to in vitro digested HT-IMF. This mucus modulation is likely supported by the bioaccessible MEM-IMF peptide, αs1-casein 23FFVAP27, released during in vitro gastrointestinal digestion of MEM-IMF but not HT-IMF. The αs1-casein 23FFVAP27 peptide increased mucin-1 and mucin-2 protein and mRNA transcripts of mucin-5AC in HT29MTX monolayers compared to untreated monolayers (P < 0.05).
In conclusion, MEM-IMF differs to HT-IMF as it (a) has faster protein digestion in a young gut, (b) promotes intestinal digestive capacity, (c) significantly increases goblet cell numbers and mucin biomarkers in the jejunum and (d) significantly reduces pathogen adhesion to an in vitro gut barrier. These gut responses for MEM-IMF are similar to gut responses reported with human breast milk. Therefore, we can consider MEM-IMF superior to HT-IMF. As such, MEM-IMF is a promising candidate in efforts to produce an IMF product that more closely resembles breast milk.
Keywords: Infant milk formula, membrane filtration, high-temperature, protein digestion, intestinal barrier health.
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Keywords
Infant milk formula , Membrane filtration , High-temperature , Protein digestion , Intestinal barrier health
Citation
Dold, C. A. 2024. Influence of infant milk formula processing on protein digestion and gut barrier health in vitro and in vivo. PhD Thesis, University College Cork.