Composition and distribution of α-dicarbonyl compounds in propolis from different plant origins and extraction processing

Abstract

α-Dicarbonyl compounds (α-DCs), mainly produced during thermal treatment and storage of sugary foods, are routinely measured to evaluate food quality. Propolis is a functional food that has gained wide usage; thus, its quality control is an emerging concern. There are no reports on distribution of α-DCs in propolis. In this study, 10 main α-DCs standards of o-phenylenediamine (OPD) derivatives were prepared and confirmed by high resolution mass spectrometry. Based on these standards, an ultra-high performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry (UHPLC-QqQ-MS/MS) was established and validated to determine the α-DCs in different propolis samples. Nine α-DCs were detected, ranging from 0.006 to 44.936 mg/kg. Methyl glyoxal (MGO), 2,3-butanedione and glucosone are rich in content, with the highest content of MGO. The level of 3-deoxypentosulose (3-DG) increased sharply with long-term storage of propolis extracts. The comparison revealed 20-fold lower levels of MGO when supercritical CO2 extraction and ethanol extraction were used, highlighting the importance of extraction techniques used in processing raw propolis. The investigation of commercially available propolis products found that α-DCs were in the range of 0.013–16.181 mg/kg. The results indicated that α-DCs can be the potential index to control propolis quality.