Photo- and Sonoactive Food Colorants Inactivating Bacteria

While dyes are commonly used as excipients in pharmaceutical and nutraceutical fields, they have a wide range of potential applications in the medical, environmental, and food industries as cytotoxic drugs and mediators for physical antimicrobial treatments. The present study aims to develop nonthermal antimicrobial methods to minimize the changes in nutritional properties and quality attributes of edible goods by using food colorants.

Rhein, a fluorescent anti-bacterial and anti-cancerous compound derived from palmatum plant, is proposed as a yellow dye candidate mediator for physical antimicrobial treatments, as well as its combination with erythrosine B (E127). This combination is suggested as a strategy to eradicate Gram-positive and Gram-negative bacteria. The sono- and photo-activity of E127 and rhein alone and in their mixture was studied against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria.

In addition, a combined sono- and photodynamic sequential treatment of E. coli bacteria cells with E127, rhein, and E127/rhein combination was investigated. Combined application of E127 and rhein caused synergetic cytotoxic activity.

The photo-dynamic activity of several other edible food colorants was studied, displaying dependance of S. aureus photodynamic eradication on dark pre-incubation time of the cells with colorants. After 30 min dark pre-incubation photodynamic activity of the colorants can be ranged as follows: E150 (Vanillin) > E150d (Vanillin) > E122 (Rum) > E124 (Red) > E129 (Red) and after 60 minutes dark incubation - E150 (Vanillin) > E122 (Rum) ~ E124 (Red) > E150d (Vanillin). A connection between chemical structure and photodynamic efficacy of some colorants is suggested.