Purpose: 1) To investigate the inactivation mechanisms of PL and PL-surfactant on E. coli O157:H7 attached on glass coverslips, and 2) observe the bacterial attachment on green onions (stems and leaves) and raspberries as well as decontamination effect of dry PL.
Methods: 1) To investigate the mechanism of PL, E. coli O157:H7 cells were attached on glass coverslips and treated by dry PL, wet PL and PL-surfactant. The ones without treatment served as control. Scanning electron microscopy (SEM) has been used to observe the bacterial morphological change before and after the treatments. 2) To compare two different fresh produce, SEM and Cryo-SEM were used to observe the surface structure of green onions (stems and leaves) and raspberries. The attachment of E. coli O157:H7 on the produce as well as their morphological change after PL treatments have also been compared.
Results: The results showed that 1) dry PL caused intracellular liquid evaporation and led to flatten out on the edge of the cells. Wet PL and PL-surfactant treated bacterial cells showed more membrane disruption; and 2) different topology of the food matrixes affected bacterial attachment.
Significance: 1) PL was proved by the SEM image to have photo-thermal effect on E. coli O157:H7 which caused a change of cell morphology, membrane disruption, and shrinking of intracellular tissues. 2) Surface structure of green onions (stems and leaves) as well as raspberries affected the attachment of bacterial cells and the surface roughness related with bacterial cell envelope structure after PL treatment.