Vulnerability of anthocyanins to the components of a thin-layer chromatographic system and comprehensive screening of anthocyanes in alimentary products

Abstract

The aim of this study was to revisit the TLC authentication of alimentary products concept based on analysis of anthocyanes with the foodstuffs of plant origin. To this effect, we used two anthocyanins (cyanin and keracyanin) and two anthocyanidins (pelargonidin and delphinidin) as phytochemical standards. The first step was to develop a novel method making use of the RP-18 F254s stationary phase (which ensures mixed-mode retention mechanism with the localized adsorption on the non-bonded silanols) and acetic acid as the mobile phase component. Importantly, similar TLC systems are currently used for the analysis of anthocyanes. Individual steps of our method development enabled a deeper insight in vulnerability of anthocyanins to external conditions resulting in hydrolysis thereof. In this study, it was impossible to fully separate the products of hydrolytic degradation of the test anthocyanins in a single development run and it was only triple development which ensured distinct and symmetrically shaped chromatographic spots, further scrutinized with use of mass spectrometry. The identity of the hydrolytically split fractions was additionally studied with use of the p-aminobenzoic acid (PABA) test. To obtain calibration curves, triple development was employed for cyanin, keracyanin, and pelargonidin, while delphinidin was developed in one development run. The respective LOD and LOQ values were: for spot (i) derived from the cyanin standard, 0.005 and 0.016 μg spot−1; for spot (ii) derived from the cyanin standard, 0.006 and 0.017 μg spot−1; for spot (i) derived from the keracyanin standard, 0.092 and 0.274 μg spot−1; for spot (ii) derived from the keracyanin standard, 0.035 and 0.104 μg spot−1; for the pelargonidin standard, 0.013 and 0.040 μg spot−1; and for the delphinidin standard, 0.036 and 0.108 μg spot−1. The developed method was used to identify and quantify cyanin, keracyanin, pelargonidin and delphinidin in selected alimentary products (syrups, juices and herbal infusions), keeping in mind that the obtained numerical results were of semi-quantitative nature only.