Text

theses

Alternatives to the use of traditional chemical antimicrobials to improve food safety are needed. Curcumin is the principal curcuminoid of turmeric and approved for food use in Europe (E100) and the USA. Curcumin has been shown to have antimicrobial effects after activation by light and potential applications in treating cavities. The challenge of curcumin application is that curcumin will rapidly degrade in physiological and alkaline conditions, while it is more stable in slightly acidic conditions. Ascorbic acid (AA), which is also referred as vitamin C, is a GRAS substance commonly used in food. It can stabilize the curcumin by lowering pH and other unknown mechanisms. The purpose of this study was to evaluate the potential effect of ascorbic acid on the phototoxicity of photosensitizer curcumin in inactivating Listeria monocytogenes (gram-positive) and Escherichia coli O157:H7 (gram-negative) foodborne pathogens. Curcumin was prepared by dissolving in 95% ethanol and diluting to desired concentrations with sterile distilled water (SDW). L-ascorbic acid was dissolved in SDW, filter sterilized, and diluted to the desired concentrations with SDW. The absorption spectrum of the curcumin with or without ascorbic acid was determined by UV/Vis spectrophotometer to ensure that no changes in absorption spectrum were found with different curcumin/AA combinations. The antimicrobial effects of the curcumin/AA were evaluated on both solid media using the modified Kirby Bauer method and liquid media. The effects of illumination time were studied in the liquid media (0, 1, 5, and 10 minutes). Overnight cultures of Listeria monocytogenes L008 and Escherichia coli O157:H7 86-24 were diluted to approximate 6.0 log CFU/mL. Curcumin, ascorbic acid, and cells were mixed and pre-incubated in the dark for 5 minutes. The mixture was then transferred to a 96-well plate for illumination treatment (450 - 455 nm, 0.13 W/cm2). The suspensions were subjected to microbiological analysis by direct plating method. A potential effect was observed for ascorbic acid on enhancing the phototoxicity of photosensitizer curcumin against both types of pathogen. Curcumin with or without AA did not show any antimicrobial effects without light exposure. Conversely, no L. monocytogenes were detected when exposed to 5 μM of curcumin and 25 μg/mL of AA, after one-minute illumination. Escherichia coli O157:H7 was not detected following treatment with 50 μM of curcumin and 25 μg/mL of AA after 10-minute light exposure. Overall, curcumin and AA combination showed higher bacterial reduction than curcumin only. This study demonstrated that curcumin/AA combination has promising inhibitory effects against Listeria monocytogenes and E. coli O157:H7, indicating a potential application as a decontamination intervention on food surfaces including meat, poultry and fresh produce.

ETD_8547

M.S.

Includes bibliographical references

by Jingwen Gao

doi:10.7282/T32F7RNG

ETD graduate

The author owns the copyright to this work.