Enhanced electric field and charge polarity modulate the microencapsulation and stability of electrosprayed probiotic cells (Streptococcus thermophilus, ST44)

Abstract

Abstract The “organization” of Streptococcus thermophilus (ST44) probiotic cells within maltodextrin microcapsules was investigated, using electrospray processing. The generated electrostatic forces between the negatively surface-charged probiotic cells and the applied negative polarity on the electrospray nozzle, allowed to control the location of the cells towards the core of the electrosprayed microcapsules. The “organization” of the cells affected the evaporation of the solvent (water) and subsequently the glass transition temperature (Tg) of the electrosprayed microcapsules. Moreover, the utilization of auxiliary ring-shaped electrodes, between the nozzle and the collector, enhanced the electric field strength and contributed further to the increase of the Tg. Numerical simulation, through Finite Element Method (FEM), shed light to the effects of the additional ring-electrode on the electric field strength, potential distribution, and controlled deposition of the capsules. Moreover, the viability of the encapsulated cells was significantly improved for up to 2 weeks of storage at 25°C and 35% RH, when the cells were located at the core of the microcapsules, compared to the probiotics distributed towards the surface. Overall, this study presents a novel method to manipulate the encapsulation of the surface charged probiotic cells within electrosprayed microcapsules, utilizing the polarity of the electric field and additional ring-electrodes.