Preliminary examination of the antimicrobial activity of lactic acid against nine bacteria (Escherichia coli, Proteus mirabilis, Salmonella enteritidis, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis, Listeria monocytogenes, Bacillus cereus and Bacillus megaterium) and three yeasts (Rhodotorula sp., Saccharomyces cerevisiae and Candida albicans) was performed using disc diffusion and broth microdilution method. At a concentration of 321 mg/mL, inhibition zones ranged from 24.0 mm (Es. coli) to 38.3 mm (En. faecalis) for the tested bacteria. The inhibition zones of the yeasts ranged from 11.3 mm (Sac. cerevisiae) to 14.0 mm (Rhodotorula sp.). Lactic acid minimal inhibitory concentration for bacteria was ≥1.25 mg/mL, while minimal biocide concentration was ≥2.50 mg/mL. Minimal inhibitory concentration for yeasts was ≥12.50 mg/mL, while minimal fungicidal concentration was ≥25.00 mg/mL. The obtained results showed that lactic acid could be used as an efficient natural antimicrobial agent improving the safety of all-natural foods.
The silica core/shell nanostructures were prepared by a wet-chemical process.
Silica core particles were prepared by hydrolysis and condensation of
tetraethylorthosilicate. The obtained particles (average size ~0.4 ?m) were
used as templates for assembling of silica nanoparticles generated from
highly basic sodium silicate solution. The silica core particles were
functionalized with 3-aminopropyltriethoxysilane (APTES) to allow
electrostatic assembling of silica nanoparticles on the surface of silica
core particles. In order to find the optimal conditions for synthesis of
silica core/shell particles with mesoporous shells, the effect of reaction
time on formation of silica nanoparticles was investigated. The effect of
process parameters on generation and aggregation of silica nanoparticles
prepared from highly basic sodium silicate solution was also investigated. It
was shown that the size of silica nanoparticles and tendency towards
aggregation increase with increasing the reaction time and temperature. These
behaviours were reflected on the formation of mesoporous silica shell around
silica core particles. Thin and uniform mesoporous silica layers were
obtained if reaction times were kept short. When the reaction time was
prolonged, the thicker and non-uniform shells were obtained. [Projekat
Ministarstva nauke Republike Srbije, br. III45021]
Two types of silica particles were synthesized by the sol-gel process. The first type of silica particles was synthesized by neutralization of a highly basic sodium silicate solution. The obtained particles were polydispersed with irregular shapes and a mesoporous structure. The second type of silica particles was prepared by hydrolysis and condensation of tetraethylortosilicate (TEOS). The obtained particles were spherical and monodispersed with a microporous structure. Multimodal size distribution was characteristic of the silica particles obtained from the sodium silicate solution with a particle size distribution between 0.2 and 6 μm. On the other hand, the silica particles obtained from TEOS had a unimodal size distribution with an average particle size of about 0.5 μm. The physical adsorption of Candida rugosa lipase onto the obtained silica particles was investigated at pH=7. The silica particles prepared from TEOS had the lowest adsorption efficiency (2%) while those prepared from the highly basic sodium silicate solution had the highest adsorption efficiency (50%). The isoelectric point of silica particles and Candida rugosa lipase was 2.5 and 2.4, respectively, which suggests that van der Waals' forces probably play the major role in the process of binding lipase into mesoporous silica when physical adsorption was involved at pH 7.
Viable Saccharomyces cerevisiae cells were immobilized by silicaalginate matrix and obtained spherical composite particles and used for biosorption of Cd(II) ions. The obtained composite displayed high cadmium removal efficiency of 99.2, 95.7, 88.3 and 78% in the successive four adsorption steps. The adsorption capacity after four step of Cd(II) removal was ~14,2 mg of Cd(II) per g of biosorbent. Pseudo-second-order kinetic agree well with the experimental values suggesting both adsorption and ionic exchange are simultaneously performed on the surface of used biosorbent.
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