Text

theses

ETD doctoral

There is an increasing demand by consumers for natural antimicrobials in foods; alternatives to conventional chemical interventions are needed. It has been found that photosensitizer(s) can inactivate a broad spectrum of microorganisms after being activated by light at appropriate wavelength; and has been proposed as an alternative to antibiotics in the clinical field. However, studies on its application on food remain limited, especially on meat and poultry. The main goal of this research was to study the antimicrobial efficacy of a water-soluble photosensitizer curcumin (PSC) and its potential for use by the poultry industry.

A light device was built based on the absorption spectrum of PSC. The absorption spectrum of PSC and the power density of the light device were characterized by spectrophotometer and spectroradiometer, respectively. The activities of PSC in inactivating Listeria monocytogenes and Salmonella were determined on media (agar & broth) and chicken skin. Factors (incubation time, light dose, and cell density) that might influence PSC activity were also evaluated. This research compared PSC with a commercially available antimicrobial for the efficacy in controlling pathogen growth and the influences on food quality (pH, color, and shelf-life) during refrigerated storage. Experiments were completed to enhance the photoinactivation efficacy of PSC by combining with CaCl2 and to study the mode(s) of action.

PSC was shown to have a strong absorption at 410 nm, so a light device (430 nm, 107 W/m2) composed of LED lights was used in this study. The minimum inhibitory concentration (MIC) of PSC for L. monocytogenes was 10 ppm, while 200 ppm of PSC resulted in maximum 3.6-log reduction on Salmonella. On chicken skin, treatment with 300 ppm of PSC led to 2.9 log CFU/cm2 and 1.5 log CFU/cm2 reduction of L. monocytogenes and Salmonella, respectively. No significant differences occurred for antimicrobial activities were found among different incubation time (1, 2.5, and 5 min) and light doses (6.4, 32.1, and 64.2 kJ/m2). For shelf-life tests, PSC showed equivalent or better efficacy in controlling the population of pathogens and commensal bacteria as the commercial disinfectant, without changing the color and the pH of chicken skin. Interestingly, the addition of 50 mg/ml of CaCl2 resulted in an additional one-log reduction of Salmonella on media than PSC alone, but no significant differences were found between PSC and PSC+CaCl2 treatment when testing on the chicken skin model. It was found that the addition of CaCl2 enhanced the membrane permeability of Salmonella cells and increased the uptake of PSC molecules, probably accounting for the higher reduction achieved.

This study suggests that PSC effectively inactivated pathogens without influencing product quality factors, indicating a potential application as an antimicrobial intervention for use by the poultry industry. Moreover, the addition of a membrane permeabilizing agent like CaCl2 facilitated the inactivation by PSC, suggesting a promising approach to improve the efficacy of photoinactivation.

ETD_11371

Ph.D.

Includes bibliographical references

doi:10.7282/t3-nvgj-2g65

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