Modeling the pulsed light inactivation of microorganisms naturally occurring on vegetable substrates

Pulsed light (PL) is a fast non-thermal method for microbial inactivation. This research studied the kinetics of PL inactivation of microorganisms naturally occurring in some vegetables. Iceberg lettuce, white cabbage and Julienne-style cut carrots were subjected to increasing PL fluences up to 12 J/cm2 in order to study its effect on aerobic mesophilic bacteria determined by plate count. Also, sample temperature increase was determined by infrared thermometry. Survivors' curves were adjusted to several models. No shoulder but tail was observed. The Weibull model showed good fitting performance of data. Results for lettuce were: goodness-of-fit parameter RMSE = 0.2289, fluence for the first decimal reduction δ = 0.98 ± 0.80 J/cm2 and concavity parameter p = 0.33 ± 0.08. Results for cabbage were: RMSE = 0.0725, δ = 0.81 ± 0.23 J/cm2 and p = 0.30 ± 0.02; and for carrot: RMSE = 0.1235, δ = 0.39 ± 0.24 J/cm2 and p = 0.23 ± 0.03. For lettuce, a log-linear and tail model was also suitable. Validation of the Weibull model produced determination coefficients of 0.88-0.96 and slopes of 0.78-0.99. Heating was too low to contribute to inactivation. A single low-energy pulse was enough to achieve one log reduction, with an ultrafast treatment time of 0.5 ms. While PL efficacy was found to be limited to high residual counts, the achievable inactivation level may be considered useful for shelf-life extension.

► Weibull model satisfactorily describes pulsed light inactivation survival curves. ► A single low-energy light pulse yields one log reduction in vegetables. ► Pulsed light efficacy is limited for high residual counts in vegetables.