Proteins from different sources in a high-fat food matrix influence lipid hydrolysis through bolus coalescence and interactions with bile salts

Bile salts (BS), as an important biosurfactant, play a vital physiological role in lipid digestion and transport. However, nutrient intake is often not uniform, and the protein-BS interaction may affect the interfacial process of lipolysis and reduce hydrolysis. In this study, an in vitro digestion model was used to explore the digestion behaviours of high-fat and high-protein diets prepared with different protein sources (pork, chicken, casein and soy protein). Interestingly, the final degree of hydrolysis of the same type and level of fat differed in the following order: casein > soy protein > pork protein > chicken protein. This difference was attributed to the findings that the salt-soluble proteins in pork and chicken effectively bound BS during intestinal digestion, reducing its efficiency in participating in fat digestion. Fluorescence spectra demonstrated that myofibrillar proteins of pork and chicken exhibited a strong binding capacity to BS. The addition of BS increased the proportion of random coils in the protein, and hydrophobic interactions played an essential role in the degree of binding. In addition, the rheological characteristics and microstructure of diets differed by protein source. Meat protein diets exhibited stronger aggregation, resulting in a smaller interface area for reaction. This in vitro study could provide a potential mechanism explaining the inhibition of fat digestion by different protein diets and provide more reasonable dietary guidance for obese people.