Étude in vitro des propriétés probiotiques des bactéries lactiques d’origine apicole et essai de formulation d’un sorbet fonctionnel à base de fruits et de Psyllium.

Abstract

The honeybee Apis mellifera intermissa hosts significant microbial biodiversity, with associated microorganisms showing exciting potential in the agro-food industry. These microorganisms represent a valuable resource for isolating novel strains of lactic acid bacteria with proven probiotic potential. This thesis focuses on the investigation of new indigenous lactic cultures with probiotic properties, isolated from the digestive tract of Apis mellifera intermissa and its honey, using cultural methods. A total of 141 presumptive lactic acid bacteria (LAB) isolates were obtained from five bees and two samples of fresh honey. Among them, 19 isolates were found to be acidresistant. Their polyphasic characterization identified them as belonging to four species: Fructobacillus fructosus, Apilactobacillus kunkeei, as well as Lactobacillus kimbladii and/or Lactobacillus kullabergensis. The isolated strains were then subjected to a series of in vitro tests to evaluate their probiotic properties and select the most effective ones. The results revealed significant variations in viability under simulated gastrointestinal conditions, as well as differences in autoaggregation and hydrophobicity levels. Broth cultures assessed using the disk diffusion method, demonstrated variable antibacterial activity against five human pathogenic strains. However, only the neutralized and catalase-treated supernatants of Fructobacillus fructosus ML20 and Apilactobacillus kunkeei U21 inhibited the growth of Escherichia coli, Bacillus cereus, and Staphylococcus aureus. Ten out of fourteen strains selected for their antibacterial activity demonstrated a significant ability to reduce cholesterol levels. The safety of the lactic strains was confirmed in vitro by the absence of hemolytic activity and biogenic amine production, along with variable sensitivity profiles to 13 tested antibiotics. Finally, a functional fruit-based frozen dessert was developed by incorporating the probiotic strain Fructobacillus fructosus ML20, selected for its interesting functional properties. Three formulations were tested: a standard one with an industrial stabilizer, a second with psyllium, and a third derived from the psyllium-based formulation by adding the ML20 strain. Although the melting kinetics favored the standard formulation, no significant differences were observed between the first two formulations in terms of physicochemical parameters, and the psyllium sorbet was preferred in sensory analysis. The ML20 strain demonstrated satisfactory viability in the product under simulated gastrointestinal conditions and after 30 days at -18 °C.These results highlight its industrial potential, particularly in the functional food sector.