Modeling the Inactivation of Listeria innocua and Escherichia coli in fresh-cut tomato treated with pulsed light

Abstract

The effectiveness of pulsed light (PL) treatments to inhibit microorganisms on fresh-cut tomatoes (Lycopersicon esculentum Mill., cv. Daniela) was investigated. Tomato slices inoculated with Escherichia coli or Listeria innocua were exposed to PL treatments (4, 6, or 8 J cm−2 fluence) and kept cold at 4 °C for 20 days. L. innocua and E. coli counts, gases in the headspace of the containers (O2 and CO2), pH, titratable acidity, and soluble solid content were monitored throughout the cold storage. The PL treatments reduced significantly (p < 0.05) initial loads of both microbes. The effect of the PL fluence on the survival number of microoganisms was described by a log-linear model (R2 = 0.849–0.999). At any fixed time within the cold storing, the microbial counts for untreated samples were always higher than those cut tomatoes that had been previously PL-treated. The behavior of L. innocua and E. coli during the storage were well adjusted (R2 > 0.930) by Gompertzian models; the studied microorganisms exhibited different patterns during the storage period. On the other hand, O2 and CO2 partial pressures in containers with fresh-cut tomatoes were also significantly affected by PL treatments (p < 0.05). The highest PL fluence caused the greatest changes of O2 and CO2 contents. In addition, the application of PL triggered an acceleration of the O2 consumption during the cold stage. PL treatments might be used to effectively extend the safety of fresh-cut tomatoes over 12 days of storage against E. coli and L. innocua growth.

The Spanish Ministry of Economy and Competitiveness (MINECO) supported this work through the project AGL 2010-21572. Authors thank the University of Lleida (Spain) and Banco Santander for awarding a Jade Plus grant. Special thanks to Ana Ramos-Villarroel for providing technical support.