Capsules as Minibioreactors: Effect of the Formulation on the Probiotic Metabolism and Confinement

Abstract

Encapsulation is a commonly used tool in the pharmaceutical and nutraceutical fields to protect the compound of interest from adverse environmental conditions (i.e., production process, gastrointestinal transit, immune defense) or to ensure a target or controlled release of an active principle. However, capsules can also be used as reactors, by which probiotics can carry out a fermentation with improved process performances. In the present work, hydrolyzed oatmeal capsules were developed as mini-bioreactors, segregating the probiotic strain in active fermentation and allowing the metabolite release. The aim was to study how composition can influence the ability to ferment and the confinement of microorganisms. Four different capsules formulations were studied varying CaCl2 and alginate concentrations [(i) 0.5% alginate-0,1 M CaCl2; (ii) 1% alginate-1 M CaCl2; (iii) 1% alginate-3 M CaCl2; (iv) 1% alginate-5 M CaCl2]. The capsules were suspended in the same hydrolyzed oatmeal suspension used to produce them and left to ferment at 37°C for 24h. Microbiological and chemical analyses were carried out on both capsules and external liquids. An increase in the bacterial concentration of about 3 logs was recognized for all the first three formulations in the capsules, while a growth inhibition was observed for the (iv) formulation, the only formulation for which microorganism confinement was also noted. The highest lactic acid production (15.9 g/L) was observed for the (ii) formulation, while the lowest one was also recorded for formulation (iv). Optical analyses confirmed the different structural characteristics of the capsules.