Antimicrobial photodynamic treatment as an alternative approach for Alicyclobacillus acidoterrestris inactivation.

Alicyclobacillus acidoterrestris is a cause of major concern for the orange juice industry due to its thermal and chemical resistance, as well as its spoilage potential. A. acidoterrestris spoilage of orange juice is due to off-flavor taints from guaiacol production and some halophenols. The present study aimed to evaluate the effectiveness of antimicrobial Photodynamic Treatment (aPDT) as an emerging technology to inactivate the spores of A. acidoterrestris. The aPDT efficiency towards A. acidoterrestris was evaluated using as photosensitizers the tetracationic porphyrin (Tetra-Py+-Me) and the phenothiazinium dye new methylene blue (NMB) in combination with white light-emitting diode (LED; 400-740 nm; 65-140 mW/cm2). The spores of A. acidoterrestris were cultured on YSG agar plates (pH 3.7 ± 0.1) at 45 °C for 28 days and submitted to the aPDT with Tetra-Py+-Me and NMB at 10 µM in phosphate-buffered saline (PBS) in combination with white light (140 mW/cm2). The use of Tetra-Py+-Me at 10 µM resulted in a 7.3 ± 0.04 log reduction of the viability of A. acidoterrestris spores. No reductions in the viability of this bacterium were observed with NMB at 10 µM. Then, the aPDT with Tetra-Py+-Me and NMB at 10 µM in orange juice (UHT; pH 3.9; 11°Brix) alone and combined with potassium iodide (KI) was evaluated. The presence of KI was able to potentiate the aPDT process in orange juice, promoting the inactivation of 5 log CFU/mL of A. acidoterrestris spores after 10 h of white light exposition (140 mW/cm2). However, in the absence of KI, both photosensitizers did not promote a significant reduction in the spore viability. The inactivation of A. acidoterrestris spores artificially inoculated in orange peels (105 spores/mL) was also assessed using Tetra-Py+-Me at 10 and 50 µM in the presence and absence of KI in combination with white light (65 mW/cm2). No significant reductions were observed (p < .05) when Tetra-Py+-Me was used at 10 µM, however at the highest concentration (50 µM) a significant spore reduction (≈ 2.8 log CFU/mL reductions) in orange peels was observed after 6 h of sunlight exposition (65 mW/cm2). Although the color, total phenolic content (TPC), and antioxidant capacity of orange juice and peel (only color evaluation) seem to have been affected by light exposition, the impact on the visual and nutritional characteristics of the products remains inconclusive so far. Besides that, the results found suggest that aPDT can be a potential method for the reduction of A. acidoterrestris spores on orange groves.

An insight on the role of photosensitizer nanocarriers for Photodynamic Therapy.

Photodynamic therapy (PDT) is a modality of cancer treatment in which tumor cells are destroyed by reactive oxygen species (ROS) produced by photosensitizers following its activation with visible or near infrared light. The PDT success is dependent on different factors namely on the efficiency of the photosensitizer deliver and targeting ability. In this review a special attention will be given to the role of some drug delivery systems to improve the efficiency of tetrapyrrolic photosensitizers to this type of treatment.