Comparison of the digestion behavior of soybean and cow milk/cream: Lipolysis, proteolysis, and bioaccessibility of fatty acids and vitamin D

Consumer interest in replacing dairy with plant-based alternatives has grown due to concerns over cow milk protein allergies, lactose intolerance, environmental and ethical considerations. In this study, the digestion kinetics of commercial soybean/cow milks and creams, selected on the basis of similar compositions and structures, were quantitatively assessed. During the gastric phase, soybean milk exhibited a higher lipolysis degree (47%) but similar proteolysis degree (15%) compared to cow milk. During the intestinal phase, soybean milk demonstrated higher lipolysis (90%) and proteolysis (87%) than cow milk, indicating that protein composition and structure affected both lipid and protein hydrolysis. At the end of gastric digestion, soybean cream showed greater proteolysis (20%) but lower lipolysis than cow milk cream, and this trend was maintained during intestinal digestion, aligning with differences in free fatty acid release. Large differences in cow milk fat and soybean oil fatty acid profiles led to contrasted fatty acid bioaccessibility, with soybean products generally exhibiting higher bioaccessibility. Vitamin D showed slightly higher gastrointestinal stability in soybean milk compared to cow milk (52% vs. 50%) but vitamin D bioaccessibility was similar (50%). Monitoring lipid droplet behavior throughout digestion suggested that evolving microstructures also likely impact digestion kinetics. These results provide an overview of digestive behaviors of plant- and animal-based milks and creams, which may contribute to the design of mixed plant-based milk products.