Methylxanthines such as caffeine, theophylline, theobromine are significant and widespread psychoactive substances. We developed the isocratic method with optimum composition of the mobile phase 90 % water: 10 % acetonitrile and confirmed repeatability of retention times and peak areas. The developed HPLC method was applied to determine the content of methylxanthines in selected types of black and green teas available on the market. Of the black teas (tea bags), the highest concentration of theobromine was found in Ceylon tea (18.98 mg.L−1). The highest concentration of caffeine was in a cup of Earl Gray tea (254.09 mg.L−1). Among loose black teas, the highest content of both theobromine and caffeine was found in Pu Erh Superior tea, where the theobromine content was 24.62 mg.L−1 and the caffeine content was 520.67 mg.L−1. Of green powder teas, highest caffeine content (306.46 mg.L−1) was in Shizuoka Matcha Premium and the highest content of theobromine (8.45 mg.L−1) was found in GABA Midori. From the loose green tea, the highest concentration of theobromine (12.85 mg.L−1) was in Lung Ching West Lake. The highest caffeine content (484.85 mg.L−1) was in Gyokuro Shizuoka Premium Tea. In both types of teas the amount of theobromine and caffeine was quantified, but the presence of theophylline was not proven. Data on contents of these metabolites in tea products are highly informative for consumers.
Biogenic amines are low-molecular-weight nitrogen compounds that are formed primarily by the decarboxylation of amino acids by microbial enzymes. These active substances are found mainly in various types of food or beverages. At certain concentrations, biogenic amines are essential for many physiological functions but toxic if consumed in large quantities. Therefore, the development and optimization of methods sensitive to determine these substances are very much needed. The determination of biogenic amines in food and beverages by the most commonly used separation methods with different types of detection is covered in this review.
Phenolic amides contained in oats (Avenanthramides; AVNs) are biologically active substances with strong antioxidant activity. In this paper, we evaluated efficiency of three C18 chromatographic columns (Symmetry, XBridge, Cortecs) with different particle technology and particle sizes for the separation of three major avenanthramides (AVN A, AVN B, AVN C). We compared columns in terms of retention times, retention factors of AVNs and in terms of other parameters such as number of theoretical plates, height equivalent to a theoretical plate, reduced plate height, resolution and in terms of peak symmetry, respectively. Limits of detection and limits of quantification of AVNs on all columns were calculated. Retention results of AVNs on individual columns showed a significant reduction in retention times of AVNs on solid core column with a particle size 2.7 μm compared to columns with particle size 3.5 μm. Within columns with 3.5 μm particles, separation on Symmetry C18 column appeared to be more efficient than on the XBridge C18 column. In general, results achieved on Cortecs C18 column can be considered as the best in terms of both separation efficiency and retention times.
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