Investigation of the effect of bacteriophage cocktail on microbial quality in the case of cold chain breakage: A case study on Escherichia coli contamination in milk

Abstract

Although the use of phages in food is a successful application, their activity should be tested in situations that simulate the conditions to which the food is exposed for more effective and widespread use. It is known that foods are frequently exposed to cold chain breakage, in which case the microbial balance in the food changes. Here, it was aimed to investigate the effectiveness of a phage cocktail against Escherichia coli in milk with different parameters and in the case of cold chain breakage. Two phages effective against Escherichia coli were isolated from raw milk and named as K12.2b and K12.4a. Both of these phages were determined to be highly specific to their hosts. The latent periods of phages were found to be 15 and 10 min, and the burst sizes were 348 and 24 PFU/cell, respectively. Transmission electron micrographs indicated that they belonged to Myoviridae family. For both phages, approximately 50% reduction in titers was observed at 70 °C. While K12.2b remained stable at pH 2–11, K12.4a was stable at pH 3–11. The bacterial reductions of 4.4–4.6 log-units were achieved at 25 °C for 24 h in milk, but it was limited to 1.2–2.7 log-units when the cold-chain (4 °C) was broken, and the temperature reached to 25 °C. Our study demonstrated that the efficacy of phages at real-state temperatures differs at temperatures simulating cold chain breakage.