Salmonella enterica in thinly sliced carrots and zucchini survives better at higher temperatures and higher relative humidity conditions

Abstract

The global increase in demand for ready-to-eat foods has been accompanied by a concerning rise in salmonellosis outbreaks linked to minimally processed vegetables (MPV). This study evaluated S. enterica survival in minimally processed carrot and zucchini under different combined conditions of temperature (6, 9 and 12 °C) and relative humidity (RH; 75, 85 and 95 %) over 168 h. The permeability and membrane potential of S. enterica cells were analyzed by flow cytometry and cell morphology was evaluated by scanning electron microscopy. Linear models for survival of S. enterica in minimally processed carrot and zucchini were developed. The adjusted R² coefficient values for survival in the first 24 h were 0.95 for carrot (temperature p ≤2e⁻¹⁶ and RH p = 0.00107) and 0.97 for zucchini (temperature p ≤2e⁻¹⁶ and RH p = 1.72e⁻⁰⁵). The adjusted R² values for the remainder of storage (24 to 168 h) remained high: 0.92 for carrots (temperature p = 2.76e⁻¹³ and RH p = 4.15e⁻¹⁰) and 0.91 for zucchini (temperature p = 1.24e⁻¹³ and RH p = 2.72e⁻⁰⁷). This suggests that the linear model is suitable for describing S. enterica behavior. S. enterica membrane permeability and degree of non-polarization of cell membranes decreased as temperature and RH increased. S. enterica showed significant morphological changes at 168 h of storage. Both temperature and RH affect S. enterica survival in minimally processed carrot and zucchini, with better survival at higher temperature and relativity humidity conditions. The models developed in this study may be useful for managing microbiological risks associated with S. enterica in MPV.