Atividade antimicrobiana de extratos da biomassa de spirulina platensis potencializada por ativação fotodinâmica

Abstract

Emerging technologies, such as photodynamic inactivation, which consists of the ability to inactivate microorganisms through the generation of reactive oxygen species from a photosensitizer, are being studied in the food area to reduce the microbial population, combined with the maintenance of the intrinsic characteristics of foods, as it is a non-thermal method. Therefore, the objective of this study was to evaluate the antimicrobial activity of extracts from Spirulina platensis biomass enhanced by photodynamic activation. The extracts were obtained through two extraction protocols, one based on extraction with potassium phosphate buffer at pH 6.5 (EST) and the other on aqueous extraction (ESA), and were compared with a commercial phycocyanin (FC). The extracts were characterized regarding phycocyanin and chlorophyll concentration by spectrophotometric method, color analysis, pH, identification of functional groups and chemical bonds by Fourier Transform Infrared Spectroscopy (FTIR) technique and singlet oxygen generation capacity by means of photoactivation kinetics. Sequentially, the extracts (ESA, EST and FC) were tested as photosensitizers in the photodynamic inactivation against strains of Salmonella Typhimurium, Escherichia coli (Gram-negative) and Staphylococcus aureus (Grampositive) in 96-well plates that were subjected to illumination with red LED light (630 nm). The ESA and EST extracts showed phycocyanin concentrations in the extract of 2.10 ± 0.02 mg/mL and 0.05 ± 0.00 mg/mL, respectively; The phycocyanin concentrations in the biomass were 26.27 ± 0.27 mg/g and 24.89 ± 0.07 mg/g of biomass, respectively. The extracts presented colors directed towards green (-a*) and blue (-b*). The pH of the extracts presented values for ESA of 7.92 ± 0.02, for EST of 6.67 ± 0.02 and FC of 6.41 ± 0.01. The extracts revealed the presence of chlorophyll in the composition. The FTIR demonstrated protein bands in the extracts, such as amide I, II and III. The ESA sample generated singlet oxygen being fitted with the exponential curve that evidenced a (k = 14 ± 2); the EST and FC extracts did not generate singlet oxygen, because they probably generated other reactive oxygen species. Photodynamic inactivation for FA at an extract concentration of 0.250 g/mL led to a logarithmic reduction of 17.13% in the microbial count for S. Typhimurium, while EST led to 29.88% at the same concentration. For the E. coli strain, the ESA extract reduced the count by 10.93% and EST led to a total reduction (100%). For the S. aureus strain, ESA and EST led to a maximum reduction of 9.32% and 9.26%, respectively, which can be inferred that there was a higher vulnerability of Gramnegative bacteria. Comparing the results of bacterial activation caused by the extracts without illumination, it can be inferred that the ESA and EST extracts, under the conditions tested, had their antimicrobial effect enhanced by photodynamic activation.