Monitoring the Bioprotective Potential of Lactiplantibacillus pentosus Culture on Pathogen Survival and the Shelf-Life of Fresh Ready-to-Eat Salads Stored under Modified Atmosphere Packaging

Globally, fresh vegetables or minimally processed salads have been implicated in several
foodborne disease outbreaks. This work studied the effect of Lactiplantibacillus pentosus FMCC-B281
cells (F) and its supernatant (S) on spoilage and on the fate of Listeria monocytogenes and Escherichia
coli O157:H7 on fresh-cut ready-to-eat (RTE) salads during storage. Also, Fourier transform infrared
(FTIR) and multispectral imaging (MSI) analysis were used as rapid and non-destructive techniques
to estimate the microbiological status of the samples. Fresh romaine lettuce, rocket cabbage, and
white cabbage were used in the present study and were inoculated with L. pentosus and the two
pathogens. The strains were grown at 37◦C for 24 h in MRS and BHI broths, respectively, and
then were centrifuged to collect the supernatant and the pellet (cells). Cells (F, ~5 log CFU/g), the
supernatant (S), and a control (C, broth) were used to spray the leaves of each fresh vegetable that
had been previously contaminated (sprayed) with the pathogen (3 log CFU/g). Subsequently, thesalads were packed under modified atmosphere packaging (10%CO2/10%O2/80%N2) and stored at 4 and 10 ◦C until spoilage. During storage, microbiological counts and pH were monitored in parallel with FTIR and MSI analyses. The results showed that during storage, the population of the pathogens increased for lettuce and rocket independent of the treatment. For cabbage, pathogen
populations remained stable throughout storage. Regarding the spoilage microbiota, the Pseudomonas
population was lower in the F samples, while no differences in the populations of Enterobacteriaceae
and yeasts/molds were observed for the C, F, and S samples stored at 4◦C. According to sensory
evaluation, the shelf-life was shorter for the control samples in contrast to the S and F samples, where
their shelf-life was elongated by 1–2 days. Initial pH values were ca. 6.0 for the three leafy vegetables.
An increase in the pH of ca. 0.5 values was recorded until the end of storage at both temperatures for
all cases of leafy vegetables. FTIR and MSI analyses did not satisfactorily lead to the estimation of
the microbiological quality of salads. In conclusion, the applied bioprotective strain (L. pentosus) can
elongate the shelf-life of the RTE salads without an effect on pathogen growth.