Encapsulation of host-derived probiotics using functional polysaccharides

• Main Author: Wong, Liqi
• Other Authors: Loo Say Chye Joachim
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/166642
• Institution: Nanyang Technological University

Probiotics can be used to address the challenge of infectious diseases in aquaculture. However, they are vulnerable to acidic gastric conditions, thereby reducing their cell viability. To solve this issue, microencapsulation is commonly used to protect probiotics from the harsh environments of the stomach. It is worth noticing that the functional properties of encapsulants are often overlooked in previous studies. Therefore, this project aims to evaluate the functionality of common encapsulants, exemplified by using polysaccharides, and fabricate a probiotic encapsulation system using selected polysaccharides that work synergistically with Enterococcus hirae, the host-derived probiotic, for Jade Perch. Needle extrusion was employed to encapsulate the bacteria with alginate and Kappa-Carrageenan (KC), with alginate being the “golden standard” for probiotic encapsulation and KC being selected based on its Short Chain Fatty Acids (SCFAs) production and the change in the gut bacteria composition after co-incubation. SCFAs serve as an energy source and promote the growth of fish, hence a higher concentration of SCFAs is more favourable. KC was found to be able to suppress the growth of an opportunistic pathogen Edwardsielle. Regarding the encapsulation process, various parameters, such as the polysaccharides concentration, the flow rate, and the temperature of the salt solution, were optimized for the ionic gelation process. The study found that 2% alginate and KC were the most suitable concentrations as they provide a good balance in the protectability and release ability. A flow rate of 1 mL/min was used as it allows the proper formation and hardening of particles. Higher flow rates resulted in extremely small particles being formed whereas lower flow rates resulted in the formation of big lumps of particles. Besides that, an ice bath must be employed during the extrusion of KC particles as KC is a thermal sensitive gel, where cooling temperature can facilitate in maintaining the shape of the particles. Furthermore, encapsulated probiotics exhibited higher cell viability than unencapsulated ones upon exposure to Simulated Gastro Fluid (SGF). For instance, encapsulation using polysaccharides improve the cell viability around 10^6 CFU/mL. Additionally, Scanning Electron Microscope (SEM) imaging at 2000× magnification confirmed the presence of spherical shape E.hirae probiotics embedded in the extruded alginate and KC microparticles, which were approximately 1-2 µm. In the future, in vivo feeding trials will be conducted for Jade Perch to evaluate the persistence of the delivered bacteria in the gut, pathogen resistance, and other performances of encapsulated probiotics, to achieve the manipulation of the host gut microbiota and increase disease resistance.