Photodynamic Inactivation of Salmonella spp. on Fresh-cut Papayas and Their Physicochemical and Nutritional Quality Changes during 405 Nm Light Emitting Diode Illumination at Different Storage Temperatures

Introduction: A 405 nm light emitting diode (LED) has recently paid the attention due to its antibacterial effect on foodborne pathogens in buffered solution or bacterial growth media. However, little research has been conducted on its effectiveness on foodborne pathogens and qualities on food matrix.

Purpose: The aim of this study was to determine the effect of 405 nm LED against Salmonella on fresh-cut papaya and to evaluate its impact on the physicochemical and nutritional qualities of illuminated papaya at different storage temperatures.

Methods: Each of Salmonella Agona, Salmonella Newport, Salmonella Saintpaul, and Salmonella Typhimurium was inoculated on the surface of fresh-cut papaya at the final concentration of 10³ CFU/cm². The inoculated fruit was illuminated by LED for 24-48 h at 4, 10 or 20°C. The irradiance of LED was 18±2 mW/cm² and the distance between LED and the surface of papaya was 4.5 cm. Quality parameters of fresh-cut papaya were analyzed after LED illumination.

Results: Strong growth inhibition of Salmonella was observed by LED illumination at 4°C, resulting in continuous decrease to 1.6–1.9 log CFU/cm² for 48 h regardless of bacterial strains. Control populations increased to 3.8–4.6 log CFU/cm² at 10°C for 36 h, whereas LED-illuminated cells inactivated or inhibited to 1.5–3.0 log CFU/cm². Salmonella populations rapidly grew in controls to 7.5–8.4 log CFU/cm² at 20°C for 24 h, while LED-illuminated cells reached to 6.3–7.0 log CFU/cm², indicating the growth delay due to LED illumination. No significant difference in color, texture, antioxidant capacity, flavonoids, β-carotene, lycopene, and ascorbic acid was observed between LED-illuminated and non-illuminated fruits regardless of storage temperatures.

Significance:  These results suggest that a chiller equipped with 405 nm LEDs could be used to preserve fresh-cut fruits at retail store, minimizing the risk of salmonellosis without deterioration.