Olive oil microemulsions were used as biomimetic model to simulate aspects of the digestion process in the small intestine. Hydrolytic activity of trypsin and alkaline phosphatase in microemulsions in the presence and in the absence of squalene and phenolic acids at pH 8.5 and 37°C was examined. In the case of trypsin kinetic constants were calculated and found Km = 0.080 ± 0.002 mM and Vmax = 3.8 × 10−5 ± 0.06 × 10−5 mM/s. When gallic acid and squalene were added, hydrolytic activity of trypsin was reduced to 77 ± 2% and 69 ± 3%, respectively. In the presence of o-, m-, and p-coumaric acid, protocatechouic acid, and caffeic acid, enzymatic activity was increased up to 142 ± 6%. Hydrolytic activity of alkaline phosphatase was inhibited in the presence of squalene and phenolic acids. To evaluate the size of the dispersed aqueous droplets in the presence and in the absence of enzymes, substrates, and antioxidants, dynamic light scattering (DLS) measurements were carried out and diameters in the range of 8.9–13.4 nm were observed. Membrane flexibility and micropolarity were studied by electron paramagnetic resonance (EPR) spectroscopy. Rotational correlation time (τR), order parameter (S), and hyperfine splitting constant (A0) of doxyl stearic acid in the microemulsions were calculated and found 2.06 ns, 0.17, and 14.30 G, respectively. These values were slightly affected in the presence of additives.
Practical applications: The main aim of the present study is to enhance our understanding on the digestibility of proteins and lipids in the presence of food antioxidants suggesting an in vitro digestion model for hydrolases based on virgin olive oil microemulsions. The information generated in this study could potentially facilitate the design and development of novel functional food formulations based on food-grade colloidal delivery systems. Since modification or fortification of different food products focusing on different areas of health concern are of growing interest among the various sectors of food industry, the proposed research results could be of particular interest.