PhD Food Science defence "Effect of Milk Protein Composition in a Model Infant Formula on In Vivo and In Vitro Gastric Digestion Behaviour and Physiological Responses"
Date and Time
Food Science lecture room 128
Final Examination for the Degree of PhD - NILOUFAR RAFIEE TARI
Dr. Michael Rogers, Chair
Dr. Milena Corredig, Co-Advisor
Dr. Ming Fan, Advisory Committee Member
Dr. Gisele LaPointe, Department Member
Dr. Mark Fenelon, External Examiner
TITLE: Effect of Milk Protein Composition in a Model Infant Formula on In Vivo and In Vitro Gastric Digestion Behaviour and Physiological Responses
ABSTRACT: Milk proteins are known to have different digestion and absorption kinetics and encrypted bioactive peptide compositions, and thus exert a range of different health-related functionalities. Objective of this work was to better investigate the effect of milk protein composition, on the protein digestion behaviour and further physiological responses of a model infant formula. Three formulas with similar nutrient content, but different protein compositions were prepared, one containing whey proteins (WP) and two containing WP and caseins at a ratio of 60:40 but differing in β-casein ratio. Different β-casein ratios were obtained by performing cold and warm microfiltration on skim milk. Formulas were submitted to a piglet model for in vivo digestion, and a standardized in vitro digestion model. Distinct differences were found in the gastric digests. In both in vivo and in vitro models, a higher aggregated structure was observed for WP-casein digests, compared to the higher fragmented WP digest. Higher viscoelastic properties were observed for the in vivo gastric clot of WP-casein formulas compared to WP formula. Due to more effective digestion kinetics, in vitro gastric digests from all three formulas had very weak viscoelastic properties and gel structure. Caseins were extensively hydrolysed to peptides during in vitro gastric digestion, while found largely present in the gastric coagulum in the stomach of the piglets during digestion of WP-casein formula. WP remained largely intact in both models. β-casein level and digestion time did not affect the physical properties and extent of protein hydrolysis of the gastric digests. WP-casein formulas resulted in higher growth perfromance, feed intake and feed efficiency in the piglets, compared with WP formula. A postprandial time-dependant, higher plasma GLP-1 concentration was observed in piglets fed WP-based formula, confirming the higher satiating effects of these proteins than caseins. Irrespective of the β-casein level, WP-casein formula induced a pro-inflammatory milieu in piglets, with a higher natural intestinal TNF-α concentration. An optimized in vitro cell culture experiment using intestinal Caco-2 cells and LPS stimulated human THP-1 macrophages, showed β-casein may exert anti-inflammatory function, as the digest with a higher β-casein level induced lower secretion of inflammatory cytokines TNF-α and IL-6. The results show that digestion pattern and immunomodulatory functions of a dairy matrix can be regulated by its protein composition, and can be applied in developing new generation of dairy matrices with specific health beneficial functionalities.