Low-moisture food matrices as probiotic carriers

Research output: Book/ReportPh.D. thesisResearch

  • Martin Sebastian Marcial Coba
The consumption of probiotics is associated with several strain-specific health benefits on the host. When administered in adequate amounts, probiotic bacteria generally execute their biological role in the gut. To this end, probiotic microorganisms must endure several stresses encountered during processing, storage, and upper gastrointestinal tract passage. Therefore, well-designed strategies, involving optimized preservation techniques and protection technologies against low pH and bile salts, must be applied in order to enhance the probiotic survival. Currently, there is an increasing interest of using indigenous commensal bacteria that are dominant members of the gut microbiota and perform special functions in the complex intestinal environment, as next-generation probiotics. Due to their high sensitivity to oxygen and difficulties for propagation, the development of a dosage protocol for next-generation probiotics is further challenged.This work presents a brief overview about the use of traditional probiotics as well as the potential functions of next-generation probiotics in connection with the key role that the gut microbiota composition plays on the host’s homeostasis and health. It also describes the techniques used for preservation, microencapsulation and addition of probiotic microorganisms into low- or intermediate-moisture food matrices (paper I). Finally, it refers to the three different studies performed during this Ph.D. project, which consisted in: (i) the evaluation of the suitability of dried date paste as a carrier of Bacillus coagulans, a proposed spore-forming probiotic; (ii) the development of a microencapsulation and subsequent freeze-drying protocol for Akkermansia muciniphila, a potential next-generation probiotic, and Lactobacillus plantarum, a traditional probiotic representative; and (iii) the evaluation of the suitability of dark chocolate as carrier of microencapsulated A. muciniphila and L. casei. In the first study (paper II), freeze-dried B. coagulans, mostly in the spore form, was added into five different dried date paste preparations with intermediate water activity (aw 0.48 -0.59). Although that range of aw has previously been described as non-optimal for maintaining the viability of non-spore-forming dehydrated probiotics, no significant variation regarding viability and spores percentage was detected after 45 days of storage at room temperature. These results suggested that the aw range was not conducive for germination events on B. coagulans and consequently limited the viability loss of the embedded strain. Furthermore, during in vitro gastric passage, B. coagulans showed no significant viability loss neither when embedded in date paste nor as free spores.In the second study (paper III), A. muciniphila and L. plantarum were separately microencapsulated in a xanthan / gellan gum gel matrix and in order to mitigate the deleterious effects of freeze-drying, different cryoprotectant solutions were tested. The application of solutions with high sugar or protein content reflected a significant improvement of the viability of both strains during freeze-drying. Additionally, L. plantarum showed to be relatively stable during 30 days of storage at 4 °C or 25 °C, while the viability loss of A. muciniphila was limited to 0.57 log CFU g-1 when stored during the same period of time at 4 °C. However, a dramatic decrease ranging between 4.06 – 4.57 log CFU g-1 was observed for A. muciniphila when stored at 25 °C for 30 days. During in vitro simulated upper gastrointestinal tract passage, microencapsulated A. muciniphila, either under fasted or fed state, showed better survival than free control cells, particularly during the gastric phase. Likewise, microencapsulated L. plantarum showed a significantly better survival than that of free cells during the entire in vitro upper GIT simulation under fasted state. In the third study (paper IV), A. muciniphila and L. casei were microencapsulated and freeze-dried, based on the protocol described above, and subsequently incorporated into a dark chocolate matrix. It was observed that the viability of L. casei remained highly stable during 60 days of storage either at 4 °C or 25 °C, while A. muciniphila showed a 0.63 and 0.87 log CFU g-1 reduction when stored at 4 °C and 25 °C, respectively, during the same lapse. This may suggest that chocolate provided an additional protective effect during storage since the survival of microencapsulated cells embedded in chocolate appeared to be more stable than that observed in the first study for only microencapsulated bacteria. Furthermore, during in vitro simulated gastric transit, both microencapsulated strains embedded in chocolate showed a significantly better survival than that of free cells. Finally, in a hedonic sensory test, dark chocolate containing placebo microcapsules were not significantly different from two commercially available chocolates. A systematic methodology for the microencapsulation of a next-generation probiotic candidate and its potential addition into a stable food matrix is presented in this dissertation. Additionally, chocolate, as well as dried date paste, are described as promising probiotic vehicles, which appear to be more attractive alternatives than the intake of food supplements in a capsule or tablet format.
Original languageEnglish
PublisherDepartment of Food Science, Faculty of Science, University of Copenhagen
Publication statusPublished - 2018

ID: 214870033