Optimization of spray drying of pseudomonas putida bacteriophage and use of the obtained bacteriophage powder for antimicrobial purposes in milk

In this study, the drying of Pseudomonas phage gh-1 (ATCC 12633-B1) bacteriophage with different carrier materials using a spray dryer was optimized, and the effectiveness of the obtained bacteriophage powder in preventing the growth of Pseudomonas putida ATCC 12633, a psychrotrophic bacterium, in milk selected as a model food was investigated. In obtaining bacteriophage powder, three independent variables (maltodextrin ratio in the carrier material, whey protein isolate ratio in the carrier material, and drying outlet temperature) were used, and the drying process carried out with a spray dryer was optimized to ensure the least loss in bacteriophage titer and the highest solubility values. Optimum bacteriophage powder production was achieved by using a solution containing 8.49% maltodextrin and 5.66% whey protein isolate as carrier material and setting the drying exit temperature to 47.1°C. Both bacteriophage powders and liquid forms of bacteriophages were stored at 4°C for 6 months. Dissolution, phage titer, particle size, dry matter, water activity, bulk density, color, glass transition temperature, and imaging analyses were performed on bacteriophage powder samples. Additionally, bacteriophage applications were carried out on milk in the 1st, 3rd, and 6th months of storage. On the first day of storage, the phage titer of the liquid bacteriophage stock solution was found to be 13 log POB/ml. On the other hand, the phage titer of the bacteriophage powder sample produced at the optimal point was found to be 11 log POB/g. While it was determined that bacteriophage samples stored in liquid form lost their viability and activity in the 3rd month of storage, it was determined that powder samples maintained bacteriophage viability and activity until the 6th month of storage. In milk samples containing Pseudomonas putida bacteria and Pseudomonas putida gh-1 bacteriophage in different concentrations (106 and 108 POB/ml) and forms (liquid and powder), proteolytic activity, viscosity, and pH values did not change during 72 hours of storage; bacterial numbers decreased and phage titers increased. As a result, it was evaluated that the bacteriophage powders obtained by spray-drying the Pseudomonas putida gh-1 bacteriophage maintained their activity during 6 months of storage and could be used to prevent the negative effects that may occur in the physicochemical properties of milk caused by Pseudomonas putida.