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.

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

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This study was funded by Ausnutria.

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Ethics committee of Wageningen University gave ethical approval for this work.

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