Preparation of silica colloidal crystal films and real-time monitoring of adsorption and degradation of various types of milk <i>via</i> the interference effect.

Abstract

Milk is rich in protein, fat, dietary fiber, and other nutrients, making it essential in a daily diet. Different processing results in varied nutritional profiles of commercial milk products. Most importantly, it is difficult to track the real-time digestion of milk in the intestines. To investigate the adsorption and degradation behavior of macromolecular substances in various processed milk types, this work optimized the preparation process for silica colloidal crystal (SCC) films and, combined with ordered porous layer interferometry (OPLI), established a label-free real-time monitoring method. We have determined that, at 30 °C, the Stöber synthesis reaction can be used to prepare monodisperse silica microspheres with an average particle size of 218.3 ± 7.5 nm. The OPLI system enabled real-time monitoring of macromolecular adsorption and enzymatic hydrolysis in five commercial processed milk samples. The results showed that the adsorption capacity of milk and processed dairy macromolecules was positively correlated with total protein and fat content, ranging from 8.4 ± 0.8 nm to 17.2 ± 0.9 nm. 0.3125 mg per mL trypsin degraded adsorbed proteins by 4.5 ± 0.6 nm to 7.8 ± 1.3 nm, while lipase at the same concentration degraded lipids by 4.2 ± 0.8 nm to 6.0 ± 0.4 nm. Milk intestinal digestion was simulated. Under the synergistic effect of trypsin and bile salts, protein degradation reached 9.5 ± 1.5 nm. This work provides an experimental basis for evaluating processed dairy products and their digestive behavior. It also provides a novel technical approach for the real-time monitoring of macromolecule adsorption and degradation in complex food environments.

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