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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.

Encapsulation is an innovative promising technique in the field of biotechnology, both for confining live microorganisms to promote their viability during processing and for the target delivery in the gastrointestinal tract, and for trapping active metabolites produced during a fermentation process within a carrier material, allowing their gradual release. During this work, a probiotic strain, Lacticaseibacillus paracasei CBA L74, was encapsulated using a hydrolyzed oatmeal suspension as a prebiotic carrier, by extrusion technique with CaCl2 a (1M) and alginate (1% w/v). The mini-bioreactors obtained were suspended in three different external liquids, (the same hydrolyzed oatmeal suspension used for the capsule production; a hydrolyzed oatmeal suspension with a modified pH equal to 3.3, and a hydrolyzed oatmeal suspension formulated by adding a specific concentration of dead bacteria) to evaluate whether the external liquid can help the confinement of the bacteria in the capsules. For this purpose, the fermentation process was carried out at 37°C for 24h; both capsules and external liquids were characterized by microbiological and chemical analyses. The maximum bacterial growth ( 109 CFU/mL) was reached in all the capsules, except for those suspended in the formulation with a modified pH where a bacterial charge of 3.5 x 108 CFU/mL was obtained; in any case, the bacterial confinement was not obtained. The highest lactic acid concentration (15.9 g/L) was observed for the capsules suspended in the same oatmeal suspension used for encapsulation, while the lowest one was obtained in the external oatmeal liquid with a modified pH.