Molecular mechanisms of the irradiation-induced accumulation of polyphenols in star anise (Illicium verum Hook. f.)

Irradiation technology has been shown to be a possible preservation technology used to prolong the shelf life and provide microbial decontamination of spices. In this study, the molecular mechanisms of the irradiation-induced accumulation of polyphenols in star anise were explored using metabolomics combined with ultra-high-performance liquid chromatography quadrupole-Orbitrap (UHPLC-Q-Orbitrap) high-resolution mass spectrom-etry. Fifty-six star anise samples from different areas processed with 2-10 kGy doses of irradiation were compared. The effect of post irradiation storage times ranging from 0 to 70 days was also evaluated. A total of 161 metabolites with variable importance on projection greater than 1 were characterized, and significant differences in flavonoid content in star anise were observed after irradiation. Absolute quantification was used for the quantification of distinctive compounds, and the limit of quantitation of the components was 1.90-6.53 mu g/ kg. The flavonoid content was stable on the 28th day of storage. The average content of flavonoids increased by 2-9 times due to the breaking of glycoside bonds in star anise by irradiation. C15H11O7+ m/z 303.13045 and C3H3O2+ m/z 71.01276 were defined as the characteristic fragments of flavonoids according to the mechanism of fragmentation. Checking the extraction ion chromatogram (EIC) characteristic fragments allows straightforward screening of untargeted flavonoids.

Automated summary

In this study, the molecular mechanisms of irradiation-induced accumulation of polyphenols in star anise were explored using metabolomics and high-resolution mass spectrometry. Significant increases in flavonoid content in star anise after irradiation were observed due to the breaking of glycoside bonds.