Release characteristic of JS25 phage microcapsules and biological control effect on liquid food

Abstract: Bacteriophages are natural enemies of bacteria and are suitable candidates for the environmentally friendly biocontrol of these pathogens. Using bacteriophages as a tool for the control of pathogens is complementary to antibiotic therapy. We have isolated a lytic bacteriophage with broad range of host, designated as JS25, which was from sewage effluent on a dairy farm in Jiangsu and was used as a biocontrol agent against Staphylococcus aureus infections. Morphologic analysis of JS25 revealed that it was closely related to other Myoviridae phages infecting Staphylococcus species. However, the stability of planktonic JS25 phages is very poor. When they are stored at 20℃, they will be inactive after 6 h, which severely restricts the widespread use of these phages. Microencapsulation is a commonly used technique for embedding active material, and this technique can not only stabilize the active substance through embedding to improve the stability, but also control the release rate of active substance by embedding technology to increase possibility of application of active substances. Although microencapsulation of active substances has been widely applied in medicine, food packaging, biotechnology, environmental protection and other fields due to many advantages, this technique can not achieve the full encapsulation of active substances, which can lead loss of some active substances during microencapsulation process. Therefore, the premise of the technology is to make the appropriate microencapsulation process for different active ingredients. In this experiment, the JS25 phage was microencapsulated by alginate, and the structure of JS25 phage microcapsule powder was characterized in order to determine the size distribution of JS25 phage powder. In addition, the stability of JS25 phage powder in different temperatures was analyzed with the control of planktonic phage. And the release and stability of microcapsules in different liquid foods were studied to determine their biological control role in liquid food. The result showed that JS25 phage powder system composed of sodium alginate and CaCl2 could be effectively constructed. And when sodium alginate and CaCl2 content were 3.72 and 2.55 g/100 mL, the embedding rate of JS25 phage could reach the maximum value of 87.43%, and the JS25 phage powder obtained under the conditions had relatively stable technology structure, and particle size in 20-90 μm was in normal distribution. Moreover, compared with the inactivation of planktonic phage, the stability of phage displayed a significant increase in this state. The phage microcapsule powder still had higher titer after 35-day storage at 4 and 20℃. In addition, JS25 microcapsules could be quickly released in different liquid foods, and also had high stability in storage. Biological control experiment results showed that with the addition of JS25 phage microcapsules increasing, the number of colonies in different liquid foods during the storage was significantly (P<0.05) reduced. JS25 phage microcapsules could significantly remove pathogens in fresh milk, egg white and broth with the dosage more than 0.1, 1.0, and 2.0 g/kg, respectively. Experimental results indicated that the microencapsulation process could effectively secure phage JS25 and had a higher biological control role to liquid food. Therefore, sodium alginate microencapsulated JS25 phage can be used for the production of JS25 phage microcapsules and the preservation of liquid food.