Microbial transglutaminase-induced cross-linking of sodium caseinate as the coating stabilizer of zein nanoparticles

In this study, a microbial transglutaminase (MTGase)-catalyzed reaction was first optimized to prepare the cross-linked sodium caseinate (MSC). At the optimal condition of MTGase to sodium caseinate mass ratio of 250 U/g and 2 h of reaction time, different concentrations of sodium caseinate (5, 25 and 50 mg/mL) were used to synthesize MTGase-catalyzed cross-linked sodium caseinate (named as MSC-5, MSC-25 and MSC-50, respectively), which were further characterized using fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), circular dichroism spectroscopy (CD) and scanning electron microscopy (SEM). Compared to those of sodium caseinate, MSC exhibited a higher molecular weight and surface hydrophobicity index, different secondary structure and microstructure characteristics. Then, MSC-50 was used as the coating stabilizer for zein nanoparticles and their composite nanoparticles (zein-MSC-50 NPs) exhibited a spherical shape with an average diameter of 240.70 nm, a narrow size distribution and negative surface charge of −23.83 mV at the optimized zein to MSC-50 mass ratio of 1:2. The stability studies indicated that zein-MSC-50 NPs had desirable re-dispersibility, thermal, salt and storage stabilities. These results suggested a possible utilization of MSC as the novel stabilizer of zein-based delivery carriers for encapsulating lipophilic bioactive components in functional foods and pharmaceutical products.