Surface decoration of whey protein microgels through the Maillard conjugation with maltodextrin

Whey proteins microgels (WPMs) are densely packed protein particles with diverse applications. However, the precipitation of the WPMs at pH values near the isoelectric point of the protein (4–5) hinders their applications. We decorated the surface of the WPMs by maltodextrin through the Maillard reaction in wet condition and investigated the influence of the reaction time on the characteristics of the particles including the colloidal stability. The pH of the WPM-maltodextrin mixture rapidly decreased from 8 to ≈7.36 during the first 60 min of the reaction, causing a glycation extent of 36%. Longer durations (≥6 h) had smaller effects on the glycation extent and extensively decreased the L* parameter of the mixture. Infra-red spectroscopy confirmed that maltodextrin reacted with whey proteins through its anomeric region. It was found by gel electrophoresis that long reaction periods (≥12 h) caused polymerization of the glycoproteins. As well, long reaction times (≥6 h) formed compact aggregates, reducing the fluoresce emission intensity of WPMs. We found that a reaction duration of 1 h, which did not cause aggregation (based on atomic force microscopy images), and increased the microenvironmental hydrophilicity of fluorophores in the WPM particles, significantly increased the colloidal stability of the particles at pH 4.0.