Growth Kinetics of Listeria monocytogenes and Salmonella enterica on Dehydrated Vegetables during Rehydration and Subsequent Storage

Abstract

Dehydrated vegetables have low water activities and do not support the proliferation of pathogenic bacteria. Once rehydrated, vegetables can be incorporated into other foods or held for later use. The aim of this study was to examine the survival and proliferation of Listeria monocytogenes and Salmonella enterica on dehydrated vegetables during rehydration and subsequent storage. Carrots, corn, onion, bell peppers, and potatoes were heat dehydrated, inoculated at 4 log CFU/g, and rehydrated at either 5 or 25 °C for 24 h. Following rehydration, vegetables were stored at 5, 10, or 25 °C for 7 d. Both L. monocytogenes and S. enterica survived on all vegetables under all conditions examined. After 24 h of rehydration at 5 °C, pathogen populations on the vegetables were generally <1.70 log CFU/g, whereas rehydration at 25 °C resulted in populations of 2.28 to 6.25 log CFU/g. The highest growth rates during storage were observed by L. monocytogenes on potatoes and S. enterica on carrots (2.37 ± 0.61 and 1.63 ± 0.18 log CFU/g/d, respectively) at 25 °C when rehydration occurred at 5 °C. Results indicate that pathogen proliferation on the vegetables is both rehydration temperature and matrix dependent and highlight the importance of holding rehydrated vegetables at refrigeration temperatures to hinder pathogen proliferation. Results from this study inform time and temperature controls for the safety of these food products.

Keywords: dried produce; foodborne pathogens; growth rates; predictive modeling.

Figure 1

Population dynamics of L. monocytogenes on rehydrated carrot (A,B), corn (C,D), onion (E,F), pepper (G,H), and potato (I,J) during storage at 5 (red circles), 10 (blue squares), or 25 °C (green triangles) for 7 days. Vegetables were rehydrated at either 5 (A,C,E,G,I) or 25 °C (B,D,F,H,J). Data are mean values ± standard deviation (n = 9).

Figure 2

Population dynamics of S. enterica on rehydrated carrot (A,B), corn (C,D), onion (E,F), pepper (G,H), and potato (I,J) during storage at 5 (red circles), 10 (blue squares), or 25 °C (green triangles) for 7 days. Vegetables were rehydrated at either 5 (A,C,E,G,I) or 25 °C (B,D,F,H,J). Data are mean values ± standard deviation (n = 9).