Miodrag L. Lazić

Comparison of Antioxidant and Antimicrobial Activities of Methanolic Extracts of the Artemisia sp. Recovered by Different Extraction Techniques

Abstract The polyphenol content, antioxidant and antimicrobial activities of the extracts obtained by classical, ultrasonic and Soxhlet extractions from dry aerial parts of two Artemisia species (Artemisia vulgaris and Artemisia campestris) were compared. Ultrasound positively affected the yield of extractive substance and the kinetics of extraction, but the extract obtained by the classical extraction showed the highest antioxidant activities and contained higher total contents of phenolic compounds and flavonoids than the extracts obtained by two other extraction techniques. Both flavonoid aglycones (apigenin, quercetin, quercetin 3,37prime;-dimethyl ether) and flavonoid glycosides (rutin, hyperoside and kaempferol 3-rhamnoside) were identified by thin layer chromatograph (TLC) analysis in the extracts from both species. A. campestris extracts were richer in quercetin than A. vulgaris and its antimicrobial activity was also better than A. vulgaris. Extracts obtained from both species were found to be more effective on the tested yeasts than bacteria. The kinetics of the total extractive substances, such as phenolic, flavonoids and quercetin extraction, was successfully described by the model of unsteady-state diffusion.

Modeling the kinetics of calcium hydroxide catalyzed methanolysis of sunflower oil.

The kinetics of Ca(OH)(2)-catalyzed methanolysis of sunflower oil was studied at a moderate temperature (60 degrees C), a methanol-to-oil molar ratio (6:1) and different catalyst amounts (from 1% to 10% based on oil weight). The methanolysis process was shown to involve the initial triglyceride (TG) mass transfer controlled region, followed by the chemical reaction controlled region in the latter period. The TG mass transfer limitation was caused by the low available active specific catalyst surface due to the high adsorbed methanol concentration. Both the TG mass transfer and chemical reaction rates increased with increasing the catalyst amount.

Antioxidant and Antimicrobial Activities of Echinacea （Echinacea purpurea L.） Extracts Obtained by Classical and Ultrasound Extraction

Abstract Antioxidant and antimicrobial activities of Echinacea purpurea L. ( Asteraceae ) extracts obtained by classical and ultrasound solvent extraction were compared. The dry aerial part of plant was extracted by 70% ethanol at a solid-to-liquid ratio of 1:10 (m/v) and 25°C. The extract obtained by classical solvent extraction contained 29% larger amounts of phenolic compounds and 20% higher content of flavonoids. 2,2-diphenyl-1-picril hydrazyl radical (DPPH) scavenging reached 93.6% and the values of EC50 were (34.16±0.65) μg·ml −1 and (65.48±1.12) μg·ml −1 for the extracts obtained by the classical and ultrasound extractions, respectively. The extracts, independent of the extraction technique applied, showed a considerable growth inhibition on Candida albicans and Saccharomyces cerevisiae , while no growth inhibition zones were observed for Aspergillus niger . The diameters of inhibition zone observed for all the microorganisms were larger for extracts obtained by classical extraction than those by ultrasound extraction.

Empirical modeling the ultrasound-assisted base-catalyzed sunflower oil methanolysis kinetics

The ultrasound-assisted sunflower oil methanolysis catalyzed by KOH was studied to define a simple empirical kinetic model useful for reactor design without complex computation. It was assumed that the neutralization of free fatty acids and the saponification reaction were negligible. The methanolysis process rate was observed to be controlled by the mass transfer limitation in the initial heterogeneous regime and by the chemical reaction in the later pseudo-homogeneous regime. The model involving the irreversible second-order kinetics was established and used for simulation of the triacylglycerol conversion and the fatty acid methyl esters formation in the latter regime. A good agreement between the proposed model and the experimental data in the chemically controlled regime was found.

Screening the Antioxidant and Antimicrobial Properties of the Extracts from Plantain (Plantago Major L.) Leaves

Abstract Antioxidant and antimicrobial activities of the extracts obtained by classical (maceration) and ultrasonic (40 kHz) extraction from dry Plantago major leaves were compared. The antioxidant activities of extracts obtained by ultrasonic and classical extraction were 0.87±0.02 and 0.85±0.02 µg/µg DPPH, respectively. Ultrasound positively affected the extractive substance yield and the kinetics of extraction, but the extract obtained by classical extraction contained higher total contents of phenolic compounds and flavonoids than that obtained by ultrasonic extraction. Extracts of P. major showed better antimicrobial activity against the yeasts than against the bacteria.

Effect of pH and aeration on dextran production by Leuconostoc mesenteroides

Dextran fermentation by Leuconostoc mesenteroides was studied under both anaerobic and aerobic conditions with and without pH control. The maximum dextran yield was obtained as a result of higher yield, stability, and activity of dextransucrase when the oxygen transfer rate in the bioreactor was equal to the maximum oxygen uptake rate of the organism, and the pH of the culture medium was 5.5.

Effects of the oxygen transfer rate on ferrous iron oxidation by Thiobacillus ferrooxidans

Abstract Ferrous iron oxidation by Thiobacillus ferrooxidans was studied in shake flasks and a bubble column under different aeration conditions. The maximum biooxidation rate constant was affected by oxygen transfer only at low aeration intensities. At oxygen transfer rates higher than 0.03 mmol O 2 l −1 min −1 , the maximum biooxidation rate constant was about 0.050 h −1 in both shake flasks of different size and the bubble column. The oxygen transfer rate could be used as a basis for scaling up bioreactors for ferrous iron biooxidation by T. ferrooxidans.

Optimization of Microwave-Assisted Extraction of Cherry Laurel Fruit

Response surface methodology was used to optimize the influence of microwave power (300–600 W), plant material-to-solvent ratio (0.05–0.2 g/cm3), and extraction time (10–30 min) on the efficiency of microwave-assisted extraction of the cherry laurel (Prunus laurocerasus L.) fruit. From experimental data, a quadratic polynomial mathematical model (R2 = 0.9949) was developed to predict the extract yield. All considered factors were statistically significant for extraction efficiency, while the most important factor was extraction time. Microwave power of 550 W, plant material-to-solvent ratio of 0.05 g/cm3, and time of 25 min were determined as optimal conditions with a maximum yield of 9.36 g/100 g fresh plant material, which was confirmed through laboratory experiments (9.12 ± 0.61 g/100 g fresh plant material). An economic condition for simultaneous maximum extract yield (7.58 g/100 g fresh plant material) with minimal energy and solvent consumption was determined by the desirability function method (18.2 min, 300 W, and 0.2 g/cm3). Additionally, the total phenol and flavonoid quantification and antioxidant activity of both extracts were tested. There is no statistically significant difference in the total flavonoid content in the extracts obtained under both proposed conditions, while the total phenolic content and antioxidant activity of the extract obtained under economic conditions were slightly lower.

Effects of aeration on extracellular dextransucrase production by Leuconostoc mesenteroides

Abstract The effect of oxygen transfer rate on extracellular dextransucrase production by Leuconostoc mesenteroides in batch fermentation without pH control was studied. The optimum aerobic conditions for both growth and dextransucrase formation were found to be at an oxygen transfer rate of about 1.0 mmol l −1 h −1 .

POWER CONSUMPTION AND GAS HOLDUP IN A GAS-LIQUID RECIPROCATING PLATE COLUMN

Abstract The pressure fluctuation at the column base is confirmed to be proportional to the vibration intensity on a power of 2 in non-gassed conditions and up to a critical vibration intensity, corresponding to the dispersion resonance frequency, in gassed conditions. The power consumption is successfully correlated with the vibration intensity and the liquid holdup. The gas holdup in both mixer-settter and emulsion regime is well correlated with the power consumption and the superficial gas velocity. The effect of the superficial gas velocity is more important than that of the power consumption. The effects of the liquid phase properties, the wetting tendency of the plate material and the fraction free area above 41% were not observed