Heat treatment of milk during powder manufacture increases casein resistance to simulated infant digestion
Résumé
Infant formulas (IFs) are major sources of proteins for the neonate when breast-feeding is not possible. Heat treatments used during IF manufacture affect the structure of milk proteins but the impact of these structural modifications on the digestion of milk proteins and the identity of the bioactive peptides released in the gut have never been studied so far. The objective of this work was to determine the impact of two technological parameters (percentage of dry matter of the milk concentrate prior to heat treatment and intensity of the heat treatment applied to it) considered as essential in IF manufacture on the resistance of milk caseins (CNs) to digestion. Six skim milk powders were manufactured by spray-drying after having submitted 25% or 35% dry matter milk concentrates to three types of heat-treatment traditionally used in industry (80°C/20 s, 85°C/180 s, 105°C/60 s). Those six samples and a reference unheated one were characterised (particle size, composition…) and submitted to an in vitro digestion model mimicking the gastrointestinal digestion of an infant. Digested samples were characterised by SDSPAGE and western-blotting and by ELISA using a collection of 23 αs1, αs2, β and κ-CN-specific monoclonal antibodies. Kinetics of β-CN hydrolysis was studied by antibody arrays. Peptides resisting to digestion were identified using mass spectrometry. Heat-treatment of milk prior to spray-drying was shown to significantly increase the residual CNs immunoreactivity monitored after digestion. Areas showing either post-translational modifications or high hydrophobicities were identified as being the most resistant to digestion whatever the process studied was. Ke