Bacteriocins have become biological weapons against harmful food pathogens and have attracted interest as tools for biopreservation. The aim of this study was to isolate, identify and characterize lactic acid bacterial (LAB) strains from cheese samples, partially purify potential bacteriocins and characterize their antimicrobial activity against pathogens. Bacteriocin-producing organisms were screened by Agar spot assay test. Initially, 25 LAB isolates were isolated from the cheese samples and identified as Lactobacillius spp., among them five strains were able to produce bacteriocin whose antimicrobial activates were analysed by agar-well-diffusion assay test against pathogenic organisms. Bacillus subtilis , Bacillus cereus , Staphylococcus aureus , Streptococcus thermophillus and Listeria monocytogens were inhibited, while Enterococcus faecalis , Salmonella typhi , Escherichia coli and Pseudomonas aeruginosa were resistant to the antimicrobial substances from LAB isolates. For optimal production of bacteriocin, LAB broth cultures were harvested at exponential phase. The molecular weights of the bacteriocins are between 7.0–15.0 kDa. The bacteriocins were characterized on the basis of their sensitivity to heat, pH, enzymes, NaCl and treatments with organic solvents. These results revealed that the bacteriocins from Lactobacillius spp. isolated from the cheese might have potential antimicrobial properties and give new insight in the development of bio-preservative agents to prevent and control pathogenic bacterial infection.
The electrical properties like AC conductivity, AC resistivity, and dielectric constant of the palm fiber-reinforced acrylonitrile butadiene styrene composites were investigated using impedance analyzer at room and variable temperatures. Palm fiber was collected from 10 trees of different age group from Comilla region in Bangladesh. Three sets of samples were prepared for three different wt (%) (5%, 10%, and 20%) of fiber contents using Injection Moulding Machine. Each set has 10 composite samples in which first five of them are made with 11 to 20 years-aged palm fiber and latter five of them are made with 5 to 10 years-aged palm fiber. The AC electric conductivity increases with the increase of frequency, wt (%) of palm fiber in the PF-ABS composites, and with the increase of temperature. The AC resistivity decreases with the increase of frequency, with the wt (%) of fiber content in the PF-ABS composites and with the increase of temperature. Moreover, the comparison between the PF-ABS composites with 11 to 20 years-aged palm tree shows better result than 5 to 10 years-aged palm tree. The dielectric constant of the composites decreases with the increase of frequency. With the addition of palm fiber content in composites, dielectric constant increases. The dielectric constant also increased with the increase of temperature.
Coccinea cordifolia (Linn.) Cogn. leaf extract showed significant mutagenic effect on Neurospora crassa fungus. Observation after 24 hours, control showed 2.9 cm linear vegetative growth of the mycelia where C. cordifolia leaf with N. crassa showed 0.25 cm growth and it is 12 times less than the control. Besides, 0.5, 1.0, 1.5, 2.0, 3.0 and 4.0 ml extract showed gradual decrease of growth of mycelia. This result indicates that this plant was suitable for induction of mutation in N. crassa. After mutation of N. crassa Ema (5297) conidia with C. cordifolia leaf extract, 6 types of mutants were found namely-dirty, ropy, albino, mat, cauliflower, conidial brand. Albino mutant showed highest frequency (35%) where ropy showed lowest frequency (5%).
Galvanizing industries of Bangladesh produce profuse amount of environmentally hazardous solid waste materials like zinc dross which contains significant amount of valuable zinc and harmful heavy lead. Zinc was extracted as zinc chloride (ZnCl 2 ) from zinc dross. Zinc stearate (ZnSt 2 ) samples were prepared by precipitation method from stearic acid, sodium hydroxide and ZnCl 2 by varying the amount of the reagents and product yield found within the range 96.06-99.18%. Characteristic peaks of ZnSt 2 were investigated by Fourier Transform Infrared Spectroscopy (FTIR). Differential Scanning Calorimeter (DSC) onset curve assigned accurate melting point within the range 122.84-124.03°C. Surface morphology of ZnSt 2 was observed by Scanning Electron Microscope (SEM) and products had semi-crystalline structure. Thermal stability of ZnSt 2 was evaluated by Thermo-gravimetric Analyzer (TGA) that complied with literature. A combination of ZnSt 2 and Calcium stearate (CaSt 2 ) at 1:1 ratio was used as thermal stabilizer in the powder commercial grade PVC resin and performed better thermal stability. The dehydrochlorination temperature of PVC with mixed stearates was 344.67±1.04°C for 10% (w/w) loading whereas for PVC, PVC with 10% (w/w) ZnSt 2 and PVC with 10% (w/w) CaSt 2 , it was 269.83±1.04°C, 317.33±1.26°C and 323.33±2.08°Crespectively.
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