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Last update: May 2021

Protein structure, a lever for infant formula optimisation

Infant formula is the most adequate substitute to human milk; however, although these two infant foods are close in terms of macronutrient content, their fine composition and structure still differ, particularly regarding proteins.

The substitution of bovine whey proteins, generally used for infant formula production, by purified bovine α-lactalbumin and lactoferrin can be a solution to better mimic the human milk protein profile. However, the heat treatments applied during infant formula production for sanitary reasons, modify the protein structure, which could alter their digestion. The objective of the present study was to evaluate the heat treatment impact, combined to different whey protein profile, on the protein structure within model infant formulas and, in turn, on their in vitro digestion.

Three infant formulas, with different whey protein profile, were heat treated between 67.5 °C and 80 °C with two different dry matter contents. These three parameters impacted the kinetics of denaturation of the whey proteins and the structure of the heat-induced aggregates within the infant formulas. More precisely, the infant formulas being the closest to human milk in terms of whey protein profile (i.e. with α-lactalbumin and lactoferrin) were less modified by the heat treatment than the infant formulas containing the total whey proteins, mostly composed of β-lactoglobulin. For the same denaturation extent (65%), the heat-induced aggregate structure depended on the infant formula composition and on the temperature and time applied.

Protein structures in the infant milk formulas (IMFs, 1.3% proteins) as observed by transmission electron microscopy. White arrows indicate partially disintegrated casein micelles. Grey solid line arrows indicate small complexes, probably soluble whey protein aggregates. Grey dotted line arrows indicate casein micelle-bound whey protein aggregates with filamentous structure. Images by Agnès Burel – Plateforme MRic BIOSIT, Rennes.

During in vitro digestion, which simulated the infant conditions, the microstructure that the infant formula adopted in the stomach depended on the protein structure, with a greater size of aggregates for the infant formula containing native casein micelles. The latest tended to have a reduced kinetics of proteolysis. Lactoferrin, when denatured, was hydrolysed faster, especially in the gastric phase. Finally, the peptide release during digestion was modulated by the protein structure and profile, particularly with bioactive peptides more numerous and resistant in infant formulas having a closer protein profile to that in human milk.

Modulating the protein structure, through heat treatment and/or protein profile, could be a lever for improving the nutritional quality of infant formula, including their physiologic impact (microbiota, intestinal epithelium development, …). This would need to be further investigated.

This work was conducted by Amira Halabi during her PhD, which was funded by INRAE and the Brittany Region. Her PhD defence took place on the 20^th of October 2020 in Rennes, Agrocampus Ouest.

Read more

Halabi, A., et al. Kinetics of heat-induced denaturation of proteins in model infant milk formulas as a function of whey protein composition (2020). Food Chem, 302, 1252-96. https://doi.org/10.1016/j.foodchem.2019.125296

Halabi, A., et al. Modification of protein structures by altering the whey protein profile and heat treatment affects in vitro static digestion of model infant milk formulas (2020). Food & Function, 11(8), 6933‑6945. DOI: 10.1039/d0fo01362e

Halabi, A. et al., Structural characterization of heat-induced protein aggregates in model infant milk formulas (2020). Food Hydrocolloids, 107, 105928. https://doi.org/10.1016/j.foodhyd.2020.105928

Contacts

Amélie Deglaire • amelie.deglaire@agrocampus-ouest.fr

Thomas Croguennec • thomas.croguennec@agrocampus-ouest.fr

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