Purpose: This work evaluated the synergistic antimicrobial activity of a food-grade compound (curcumin) with UV-A light radiation.
Methods: Bacterial samples were treated with curcumin and exposed to UV-A light under different experimental conditions (i.e. curcumin concentration, UV-A light radiation time, pH, temperature, chemical oxygen demand). After treatment, microbial counts were determined by the plate counting method.
Results: The antimicrobial activity of photo-activated curcumin was dependent on the curcumin concentration. Treatments with five ppm of curcumin were able to reduce the bacterial load from 6 log CFU/mL to levels below the limit of detection (1 log CFU/mL). Furthermore, the antimicrobial activity was significantly enhanced at lower pH (P < 0.01); but, not influenced by treatment at room and refrigerated temperatures (P > 0.05). Even though increased chemical oxygen demand (COD) in solution reduced the antimicrobial activity of photo-activated curcumin, five log CFU/mL microbial inactivation was observed for bacteria in the presence of high COD (1000 ppm). During simulated spinach washing, a five minute treatment with curcumin + UVA light lowered the bacterial count in solution from five log CFU/mL to levels below the detection limit of one log CFU/mL. In addition, cross-contamination to spinach leaves was significantly reduced as compared to UV-A light by itself (P < 0.01).
Significance: In summary, this study illustrates the potential of combining the food-grade compound curcumin and UV-A light to achieve bacterial load reduction in fresh produce sanitation.