Zoran B. Todorović

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.

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.

Correlation between Antimicrobial, Antioxidant Activity, and Polyphenols of Alkalized/Nonalkalized Cocoa Powders

Many factors can influence antioxidative and antimicrobial characteristics of plant materials. The quality of cocoa as functional food ingredient is influenced through its processing. The main aim of this study was to test if there is difference in polyphenol content, antioxidant capacity, and antimicrobial activity between nonalkalized and alkalized cocoa powders. To estimate polyphenol and flavonoid content in cocoa samples the spectrophotometric microassays were used. Flavan-3ols were determined with reversed-phase high-performance liquid chromatography (RP-HPLC). Antimicrobial activity against 3 Gram positive bacteria, 4 Gram negative bacteria and 1 strain of yeast was determined using broth microdilution method. Total polyphenol content was 1.8 times lower in alkalized cocoa samples than in natural ones. Epicatechin/catechin ratio was changed due to the process of alkalization in favor of catechin (2.21 in natural and 1.45 in alkalized cocoa powders). Combined results of 3 antioxidative tests (DPPH, FRAP, ABTS) were used for calculation of RACI (Relative Antioxidant Capacity Index) and GAS (Global Antioxidant Score) values that were consistently higher in natural than in alkalized cocoa extracts. Obtained results have shown significant correlations between these values and phenolic content (0.929 ≤ r ≤ 0.957, P < 0.01). Antimicrobial activity varied from 5.0 to 25.0 mg/ml (MICs), while Candida albicans was the most sensitive tested microorganism. Cocoa powders subjected to alkalization had significantly reduced content of total and specific phenolic compounds and reduced antioxidant capacity (P < 0.05), but their antimicrobial activity was equal for Gram-positive bacteria or even significantly enhanced for Gram-negative bacteria.