Abstract
Brazilian green propolis is a complex mixture of natural compounds that is difficult to analyze and standardize; as a result, controlling its quality is challenging. In this study, we used the positive and negative modes of ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time of flight mass spectrometry in conjunction with high-performance liquid chromatography for the identification and characterization of seven phenolic acid compounds in Brazilian green propolis. The optimal operating conditions for the electrospray ionization source were capillary voltage of 3500 V and drying and sheath gas temperatures of 320 °C and 350 °C, respectively. Drying and sheath gas flows were set to 8 L/min and 11 L/min, respectively. Brazilian green propolis was separated using the HPLC method, with chromatograms for samples and standards measured at 310 nm. UPLC-ESI-QTOF-MS was used to identify the following phenolic compounds: Chlorogenic acid, caffeic acid, isochlorogenic acid A, isochlorogenic acid B, isochlorogenic acid C, caffeic acid phenethyl ester (CAPE), and artepillin C. Using a methodologically validated HPLC method, the seven identified phenolic acids were then quantified among different Brazilian green propolis. Results indicated that there were no significant differences in the content of a given phenolic acid across different Brazilian green propolis samples, owing to the same plant resin sources for each sample. Isochlorogenic acid B had the lowest content (0.08 ± 0.04) across all tested Brazilian green propolis samples, while the artepillin C levels were the highest (2.48 ± 0.94). The total phenolic acid content across Brazilian green propolis samples ranged from 2.14–9.32%. Notably, artepillin C quantification is an important factor in determining the quality index of Brazilian green propolis; importantly, it has potential as a chemical marker for the development of better quality control methods for Brazilian green propolis.
Highlights
Propolis is a type of fragrant, gelatinous substance obtained by bees collecting the bud secretions and resins of pine trees, poplars, and other plants
The biggest advantage of ultra-performance liquid chromatography (UPLC) was the quick separation of Brazilian green propolis alcohol extracts, which greatly improved the efficiency of the test
The relative standard deviation (RSD)% values of each compound as well as the chromatogram similarity are calculated; all results indicated that instrument variability was sufficiently low at low concentrations. These results showed that the RSD% of each phenolic acid in peak area is less than 2% and similarity of the chromatogram of each standard mixture sample was more than 98%
Summary
Propolis is a type of fragrant, gelatinous substance obtained by bees collecting the bud secretions and resins of pine trees, poplars, and other plants. Molecules 2019, 24, 1791 anti-viral, anti-tumor, and anti-oxidative properties, as well as the ability to regulate blood lipids and blood sugar. As a result, it has gradually become a hot spot in nutrition research [2]. The composition of propolis is complex and may be affected by plant strain and the geographical environment of the collection; in turn, this complexity is closely related to ultimate biological properties. According to the current literature, there are at least 300 compounds of Brazilian green propolis [5]. Advances in the identification and characterization of phenolic compounds are expected to provide reliable quality control metrics for Brazilian green propolis. Characterization of a single phenolic acid obtained from
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