Effect of encapsulation and natural polyphenolic compounds on bacteriophage stability and activity on Escherichia coli in Lactuca sativa L. var. longifolia

The goals of the present study were to characterize the phages isolated by magnetic nanocomplex, to determine the effect of natural polyphenols on phage activity against E. coli and the stability of free and encapsulated bacteriophages under UV irradiation, and their efficacy against E. coli on romaine lettuce (Lactuca sativa L. var. longifolia) as a fresh food model. The morphology of the two magnetically isolated phages were characterized using the transmission electron microscope (TEM). All isolated phages were classified in a morphological family of tailed phages of the order Caudovirales, Myoviridae family. The PCR results showed that the stx1 and cI genes were not on any phage. Assays were carried out to determine the effect of four polyphenolic natural extracts on phages under UV radiation. The highest activity and stability of phages expressed in phage titer (PFU/ml) were observed in the presence of polyphenols from tarbush leaves (Flourensia cernua DC). Coliphages were encapsulated in alginate/chitosan and alginate/PVA carriers with and without polyphenols from tarbush leaves. Encapsulation led to a higher phage stability under UV radiation. All encapsulated formulations and free coliphages were applied on the surfaces of romaine lettuce containing E. coli cells. An effective reduction of 2 log of E. coli titers from lettuce was observed. Encapsulated phage formulations with and without polyphenols from tarbush leaves could be considered for future application in fresh food preservation.