Antimicrobial curcumin-mediated photodynamic inactivation of bacteria in natural bovine casing.

BACKGROUND: Outbreaks related to food contamination by resistant microorganisms is a worldwide concern that, motivates industries and research institutions to search for affordable solutions. Among the solutions that have been proposed, Photodynamic Inactivation (PDI) of microorganisms has gained prominence, among other aspects, because it is easy to apply and does not generate microbial resistance. METHODS: In this study, we used the association between curcumin solubilized with Tween and light in the photodynamic inactivation process, using light-emitting diodes with a wavelength of 430 nm for decontamination S. Typhimurium and K. pneumoniae from bovine casings used as wrappers for meat products. The result was verified by counting and comparing the number of colony-forming units of the treatment concerning the negative control. RESULTS: The solubilizer, Tween 80, used does not change the optical absorption of curcumin. An optical fluence of 150J/cm2 induces a microbial log reduction of 3.8±0.2 and 2.7±0.1 for S. Typhimurium, and K. pneumoniae contaminated guts, respectively. For the 200µM concentration of curcumin, the PDI provided a microbial log reduction of 3.16±0.03 for S. Typhimurium. For K. pneumoniae, the minimal inhibitory concentration of curcumin occurs up to 12.5µM, causing an microbial log reduction of 2.08±0.03. CONCLUSION: Both curcumin and tween are already used as additives in food production and do not pose health risks at the concentrations used. Furthermore, in the case of the material studied, the addition of curcumin favors the organoleptic quality associated with the color of the food, unlike the green or blue photossensitizers. The results pave the way for possible application of curcumin in finished meat products.

Growth inhibition of lactic acid bacteria in ham by nisin: a model approach.

Lactic acid bacteria (LAB) have been described as spoilage organisms in vacuum-packed cooked ham. A Fractional Factorial Design was performed to investigate the relative merits of sodium chloride, sodium lactate, sodium tripolyphosphate, sodium erythorbate, nisin and pediocin, in limiting the Lactobacillus sakei growth in broth culture. This allowed rejection of sodium chloride, sodium lactate and sodium erythorbate (no significant effects on growth), and a Central Composite Rotatable Design broth culture study was performed comparing the effects of nisin and pediocin. From this study, nisin was identified as a more important variable for inclusion into a cooked ham model (significant effects on growth parameters: logarithmic increase in the population, exponential microbial growth rate and lag phase extension). The validation of this outcome in a model formulation of vacuum-packed sliced cooked ham (0.001%, 0.007% and 0.013% of nisin) stored for 60days, confirmed the inhibitory effect of nisin on total LAB growth.