Chromium (VI) Inhibition of Low pH Bioleaching of Limonitic Nickel-Cobalt Ore

Limonitic layers of the regolith, which are often stockpiled as waste materials at laterite mines, commonly contain significant concentrations of valuable base metals, such as nickel, cobalt, and manganese. There is currently considerable demand for these transition metals, and this is projected to continue to increase (alongside their commodity values) during the next few decades, due in the most part to their use in battery and renewable technologies. Limonite bioprocessing is an emerging technology that often uses acidophilic prokaryotes to catalyse the oxidation of zero-valent sulphur coupled to the reduction of Fe (III) and Mn (IV) minerals, resulting in the release of target metals. Chromium-bearing minerals, such as chromite, where the metal is present as Cr (III), are widespread in laterite deposits. However, there are also reports that the more oxidised and more biotoxic form of this metal [Cr (VI)] may be present in some limonites, formed by the oxidation of Cr (III) by manganese (IV) oxides. Bioleaching experiments carried out in laboratory-scale reactors using limonites from a laterite mine in New Caledonia found that solid densities of ∼10% w/v resulted in complete inhibition of iron reduction by acidophiles, which is a critical reaction in the reductive dissolution process. Further investigations found this to be due to the release of Cr (VI) in the acidic liquors. X-ray absorption near edge structure (XANES) spectroscopy analysis of the limonites used found that between 3.1 and 8.0% of the total chromium in the three limonite samples used in experiments was present in the raw materials as Cr (VI). Microbial inhibition due to Cr (VI) could be eliminated either by adding limonite incrementally or by the addition of ferrous iron, which reduces Cr (VI) to less toxic Cr (III), resulting in rates of extraction of cobalt (the main target metal in the experiments) of >90%.

Newly Synthesized Benzothiazole Derived Ligand and its Co(III) and Ru(III) Complexes as Biological Potent Molecules: Chemical Preparation, Structure, Antimicrobial, in vitro and in vivo Cytotoxicity Studies

Herein we describe the synthesis of 2-((E)-(2-(benzo[d]thiazol-2-yl)phenylimino)methyl)-5-methoxyphenol imine base (BMM) and its metal complexes such as [Co(BMM)2] C1, [Co(BMM)(ph)] C2, [Ru(BMM)2] C3 and [Ru(BMM)(ph)] C4. The ligand and its complexes were characterized by spectroscopic, TGA, Powder X-ray diffraction (XRD), and elemental analysis. The coordination number and geometry were confirmed by various experimental data. The Co(III) and Ru(III) complexes are assigned to be having octahedral geometry. Further, the experimental results revealed that complex C2 and C4 emerged as moderate DNA binding intercalators compared to standard intercalators and prominent nuclease activity compared with C1 and C3 complexes. The extent of interaction and intercalation mode was confirmed by monitoring electronic absorption studies, fluorescence quenching probe, and viscosity measurement. Furthermore, the complexes C1-C4 were investigated for their in vitro cytotoxic studies against a panel of human cancer cell lines, viz., A549, NIH3T3, MCF-7, and EAC. Also, the cell adhesion and migration behavior were carried out after administering the complex C2 and C4 to respective cancer cell lines. In mice, the toxicities and tolerabilities of the complex C2 and C4 were also investigated through in vivo studies. The resultant complexes were screened for their microbial inhibition studies through the good diffusion method. All the complexes display moderate microbial inhibition properties compared to their uncoordinated analog.

Selection of the Most Reliable Method for the Analysis of Inhibitory Substances in Raw and Skimmed Milk

Milk used for human consumption must comply with the European Union legislative requirements for residues of inhibitory substances in milk, the values of which must not exceed the established maximum residue limit. In order to ensure the quality and safety of milk and milk products placed on the market, the presence of residues of inhibitory substances should be monitored and verified. The aim of our study was to select the most reliable method for the analysis of residues of inhibitory substances in milk. In the search for the most reliable method, a total of 49 milk samples were tested in the form of raw milk, skimmed milk and skimmed-milk powder throughout the agri-food chain. For comparison, the microbial inhibition tests Eclipse 50, Eclipse Farm, Explorer 2.0, Delvotest®, Premi®Test and the fast receptor screening test TwinSensor were used. The most relevant results were obtained by the Eclipse 50 and Eclipse Farm tests, the reliability of which were also confirmed by the Explorer 2.0 and Premi®Test tests. Moreover, according to the State Veterinary and Food Administration of the Slovak Republic, Eclipse 50 is an official reference method for the determination of residues of inhibitory substances in milk. Therefore, we can only state that of all the methods used, the Eclipse 50 seems to be the most reliable for routine control analysis of residues of inhibitory substances in all types of milk.

Biostimulation of Bacteria in Liquid Culture for Identification of New Antimicrobial Compounds

We hypothesized that environmental microbiomes contain a wide range of bacteria that produce yet uncharacterized antimicrobial compounds (AMCs) that can potentially be used to control pathogens. Over 600 bacterial strains were isolated from soil and food compost samples, and 68 biocontrol bacteria with antimicrobial activity were chosen for further studies based on inhibition assays against a wide range of food and plant pathogens. For further characterization of the bioactive compounds, a new method was established that used living pathogens in a liquid culture to stimulate bacteria to produce high amounts of AMCs in bacterial supernatants. A peptide gel electrophoresis microbial inhibition assay was used to concurrently achieve size separation of the antimicrobial peptides. Fifteen potential bioactive peptides were then further characterized by tandem MS, revealing cold-shock proteins and 50S ribosomal proteins. To identify non-peptidic AMCs, bacterial supernatants were analyzed by HPLC followed by GC/MS. Among the 14 identified bioactive compounds, 3-isobutylhexahydropyrrolo[1,2-a]pyrazine-1,4-dione and 2-acetyl-3-methyl-octahydropyrrolo[1,2-a]piperazine-1,4-dione were identified as new AMCs. Our work suggests that antimicrobial compound production in microbes is enhanced when faced with a threat from other microorganisms, and that this approach can rapidly lead to the development of new antimicrobials with the potential for upscaling.

Bioactive Compounds from Agricultural Residues, Their Obtaining Techniques, and the Antimicrobial Effect as Postharvest Additives

Agricultural vegetable products always seek to meet the growing demands of the population; however, today, there are great losses in supply chains and in the sales stage. Looking for a longer shelf life of fruits and vegetables, postharvest technologies have been developed that allow an adequate transfer from the field to the point of sale and a longer shelf life. One of the most attractive methods to improve quality and nutritional content and extend shelf life of fruits and vegetables is the incorporation of bioactive compounds with postharvest technologies. These compounds are substances that can prevent food spoilage and the proliferation of harmful microorganisms and, in some cases, act as a dietary supplement or provide health benefits. This review presents an updated overview of the knowledge about bioactive compounds derived from plant residues, the techniques most used for obtaining them, their incorporation in edible films and coatings, and the methods of microbial inhibition.

Green and Healthier Alternatives to Chemical Additives as Cheese Preservative: Natural Antimicrobials in Active Nanopackaging/Coatings

The side effects and potential impacts on human health by traditional chemical additives as food preservatives (i.e., potassium and sodium salts) are the reasons why novel policies are encouraged by worldwide public health institutes. More natural alternatives with high antimicrobial efficacy to extend shelf life without impairing the cheese physicochemical and sensory quality are encouraged. This study is a comprehensive review of emerging preservative cheese methods, including natural antimicrobials (e.g., vegetable, animal, and protist kingdom origins) as a preservative to reduce microbial cheese contamination and to extend shelf life by several efforts such as manufacturing ingredients, the active ingredient for coating/packaging, and the combination of packaging materials or processing technologies. Essential oils (EO) or plant extracts rich in phenolic and terpenes, combined with packaging conditions and non-thermal methods, generally showed a robust microbial inhibition and prolonged shelf life. However, it impaired the cheese sensory quality. Alternatives including EO, polysaccharides, polypeptides, and enzymes as active ingredients/nano-antimicrobials for an edible film of coating/nano-bio packaging showed a potent and broad-spectrum antimicrobial action during shelf life, preserving cheese quality parameters such as pH, texture, color, and flavor. Future opportunities were identified in order to investigate the toxicological effects of the discussed natural antimicrobials’ potential as cheese preservatives.

Antimicrobial Properties of Acrylic Resin Incorporated with Propolis Nanoparticles

Objectives: One of the main problems with polymethyl methacrylate (PMMA) used for the fabrication of oral removable appliances is plaque accumulation due to surface porosities. Incorporation of antimicrobial agents in this material might help tackle this problem. The aim of this study was to evaluate the antimicrobial activity of PMMA acrylic resin incorporated with propolis nanoparticles (PNPs). Materials and Methods: Antimicrobial properties of acrylic resin incorporated with PNPs were assessed against Streptococcus mutans (S. mutans), Streptococcus sanguinis (S. sanguinis), Lactobacillus acidophilus (L. acidophilus) and Candida albicans (C. albicans). Acrylic discs were fabricated in four groups: A control group without PNPs and three experimental groups containing 0.5%, 1% and 2% concentrations of PNPs. Disc agar diffusion (DAD) test was performed to determine the antimicrobial effects of PNPs by measuring the microbial growth inhibition zones on Muller-Hinton agar plates. The eluted components test evaluated the viable counts of microorganisms in liquid medium after 24 and 72h. Finally, biofilm inhibition test assessed the efficacy of PNPs for inhibition of biofilm formation. P<0.05 was considered significant. Results: The acrylic discs failed to produce microbial inhibition zones in the DAD test. Discs containing 1% and 2% nanoparticles showed anti-biofilm effects on all four microbial species. The colony counts of all microorganisms significantly decreased following exposure to liquids containing nanoparticles after 24 and 72h in eluted component test. Conclusion: PMMA acrylic discs incorporated with PNPs presented some antimicrobial properties against S. mutans, S. sanguinis, L. acidophilus, and C. albicans.