Engineering Strategies for Broadening Bacteriophage Application in the Food Supply Chain

Abstract

Bacterial contamination of food is a global concern. Methods of treating bacterial contamination are limited. Bacteriophages, bacterial viruses, offer a promising solution. However, bacteriophages may have limited application for foods that undergo sterilization processing, are inhospitable to organisms, or must be maintained in a dry state. This thesis focused on methods to expand the application of bacteriophages. First, bacteriophages were subjected to generalized stresses of desiccation, heat, and acidity, under laboratory conditions to propagate new populations with improved stress resistance. However, testing of these stress-resistant populations under real-world conditions failed to produce results comparable to generalized laboratory conditions. Success in the application of selected bacteriophages may require high situational specificity during selection, including in terms of food matrix and stress mechanics. The focus of our research shifted from the modification of bacteriophage populations themselves to the development of food-safe protective matrices. Designed matrices encapsulate bacteriophage for integration with modern food production and even the food products themselves. A pullulan-trehalose sugar powder was developed for the protection of a model bacteriophage from pasteurization. Microparticles were engineered such that the majority of the particle would be composed of trehalose as a stabilizer and polysaccharide pullulan was designed to accumulate at the particle surface to slow dissolution. This structure resulted in a bacteriophage powder that remained intact and protective over short-term high-temperature pasteurization, whereas unprotected bacteriophage experienced significant loss in titer. Leucine-lactose and leucine-lactose-maltodextrin microparticles were engineered for the inclusion of bacteriophage in powdered infant formula. The bacteriophage powder was designed as a dormant protection system that could activate upon reconstitution. The excipient system was formulated to not significantly affect the pH, composition, and dissolution of commercial infant formula. The bacteriophage powder was also engineered to match the shelf life and secondary shelf life of infant formula. Altogether, this thesis demonstrates that bacteriophage application in different foods can be expanded through particle engineering.