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Background: The efficacy of photodynamic therapy (PDT) depends on the combination of light and a photosensitizer for inactivation of microorganisms. However, finding the ideal conditions for the factors involved in this technique is time and cost-consuming. The rotational composite central design (RCCD) is a tool that can be allied with PDT to achieve precise results within a shorter working time. Methods: This study used the response surface methodology to optimize the parameters of PDT mediated by Erythrosine (ERY) and green light-emitting diodes (LED) in different Escherichia coli strains by applying RCCD. Results: The RCCD predicted optimum values of ERY and light exposure on PDT. According to the experimental results, the light exposure time showed the most significant influence on the inactivation of the evaluated bacteria. The optimized operating conditions were validated in laboratory tests, and no viable cells were recovered with ERY at 116 µmol L−1 and 30 min of light (33.34 J cm2) for E. coli ATCC 25922, 108 µmol L−1 and 40 min (44.38 J cm2) for E. coli ATCC 35218, and 108 µmol L−1 and 29.3 min (32.5 J cm2) for E. coli O157:H7 EDL 933. Conclusion: The adjusted polynomial models provided accurate information on the combined effects of ERY and lighting time with green LED on PDT. The application of the RCCD, in addition to reducing the number of experiments, also allows for increased quantity and quality of the results. Therefore, surface response methodology combined with PDT is a promising approach to inactivate E. coli.

The use of edible coating is an option to improve food quality and increase product shelf life. Photodynamic therapy and acid addition may be another option which decreases the number of viable microorganism cells, including Gram-negative bacteria. The present work aimed to evaluate the application of edible coatings that have the ability to inhibit the growth of Escherichia coli, using acidic pH and photodynamic therapy, in order to increase shelf life of fresh cheese. Coatings were prepared with the addition of lactic, malic and citric acids. The control coating micrograph showed surface stains, and crystal formation was apparently accentuated by the presence of citric and malic acid, not observed in the control coating or lactic acid coating. The surface micrograph of the lactic acid alginate coating showed greater homogeneity without stains and cracks. The addition of citric acid to the coating was the best result for in vitro bacterial survival tests and was therefore chosen, this coating decreased microbiological counts in the first 7 days with smaller weight loss, controlled acidity and pH and lipid oxidation remained as expected.