Search results

(1 - 1 of 1)

Title

Effect of pH on desiccation survival of Salmonella

Creator

Chen, Fangyu

Date

2019

Description

One intrinsic property of foods, pH, can affect Salmonella survival in high-moisture foods, but its effect in low-moisture foods is unknown....
Show moreOne intrinsic property of foods, pH, can affect Salmonella survival in high-moisture foods, but its effect in low-moisture foods is unknown. In this study, the effect of pH on desiccation and persistence of Salmonella was explored using two approaches. First, the pH range that affects survival in low-moisture environments was explored. The effect of acid adaptation in acidic low-moisture environments was also explored. Salmonella Anatum was grown on trypticase soy agar with 0.6% yeast extract (TSAYE). After harvest, cells were divided and one portion treated independently at pH 3, 4, 5, 7, and 8 for 30 min. Both portions were then desiccated on a cellulose filter in a biohazard cabinet (23±2°C) overnight (24±2 h). After desiccation, cells not previously pH treated were resuspended in buffers at pH 3, 4, 5, 7, and 8 for 30 min, and cells previously pH treated were resuspended in buffered peptone water (BPW). All suspensions were plated on TSAYE with ammonium iron citrate and sodium thiosulfate to determine surviving populations. In addition, S. Anatum was grown on TSAYE adjusted to pH 4, 5, 7, and 8. Cells were either harvested with buffer with the same pH of the growth media or with saline then treated at pH 4, 5, 7 and 8. All were desiccated as indicated before. Desiccated cells were stored at 20% RH at 25°C for up to 29 days. To determine the effect of prior acid adaptation on survival in acidic environments, Salmonella Anatum and Salmonella Agona were grown on agar with or without 1% glucose, harvested, then suspended in buffer at pH 4, 5, and 7. Each culture was desiccated on cellulose filters and stored at 30% RH at 25°C for up to 29 days. Harvested cells were also stored in buffers at the same pH held stored at 25oC for the same time periods. In addition, acid-adapted cells were harvested with saline, desiccated and stored as indicated for each type of cells on wheat flakes. Results from pH range finding experiments indicated pH did have an effect on the survival of Salmonella during desiccation. Desiccation prior to treatment will affect survival at different pH levels. However, prior pH adaptation did not result in increased survival under different pH conditions once cells were desiccated. Acid adaptation prior to desiccation at low pH adversely affected survival for S. Agona but not S. Anatum. Survival after desiccation at different pH levels was greater than survival in the same pH buffers. No advantage or differences in survival was observed with a commercial wheat flake product indicating results obtained in a model environment may be reduced or eliminated when food components are present.
Show less