Gastric digestion and amino acid concentrations of casein from cow and goat milk: a randomized crossover trial in healthy men

Background: In vitro studies show that goat milk proteins form less compact coagulates in the stomach compared to cow milk proteins. This may increase the accessibility of the proteins to digestive enzymes, thereby resulting in enhanced gastric digestion and amino acid (AA) absorption. However, this needs to be confirmed in vivo in humans. Objective: This study aimed to examine gastric digestion and amino acid concentrations of cow milk-derived casein (cow MC) and goat milk-derived casein (goat MC). Methods: In this single-blind randomized cross-over study 18 men (age 23 +- 1.6 years, BMI 23 +- 1.6 kg/m2) consumed 300 ml of a drink containing either 30 g of cow MC or goat MC. Participants underwent gastric MRI scans at baseline and t = 3, 10, 20, 30, 40, 50 and 60 minutes after the start of consumption. Blood samples were drawn at baseline and up to 4 hours postprandially to determine AA concentrations. In addition, participants verbally rated their appetite after each MRI measurement. Primary outcomes were gastric emptying and AA concentrations. The secondary outcome was gastric coagulation as inferred by image texture measures. Results: Gastric emptying half-time was 80 +- 25 minutes for goat MC and 85 +- 24 minutes for cow MC (p = 0.395). In line with this, gastric emptying of the drinks over time was similar (MD 0.77, 95% CI [-6.9, 8.5], p = 0.845). Serum essential AA (MD -110 umol/L, 95% CI [-162, -58]) and branched chain AA (MD -65 umol/L, 95% CI [-101, -29]) were significantly higher over time for cow MC (both p < 0.001). The image texture measure contrast was significantly lower for the cow MC compared with the goat MC drink (MD 0.010, 95% CI [0.001, 0.020], p = 0.036). Conclusion: Cow MC and goat MC have different coagulating properties, as measured by AA concentrations and supported by image texture analysis. This possible difference in coagulation did not influence overall gastric emptying or the emptying of the liquid and coagulated fractions, which were similar. This warrants further research to examine differences in casein coagulation in vivo in the food matrix of milk products to help determine the optimal use for cow and goat milk and their protein fractions. ### Competing Interest Statement Elise J.M. van Eijnatten: no conflicts of interest Guido Camps: no conflicts of interest Wolf Rombouts: during the study employed as a scientist at Ausnutria Linette Pellis: during the study employed as a scientist at Ausnutria Paul A.M. Smeets: no conflicts of interest ### Clinical Trial NL8137 ### Funding Statement This study was funded by Ausnutria. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics committee of Wageningen University gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Deidentified individual participant data that underlie the reported results will be made available upon reasonable request.