Polyphenols and flavonoids in water caltrop shells from different producing areas of China: Identification, green extraction and quantitative analysis

Water caltrop shells are typically discarded as waste. Recent research has revealed that these shells are rich in bioactive compounds such as polyphenols and flavonoids, and suggesting they possess significant potential for recovery and utilization. This study identified six polyphenols, including pyrogallol and naringenin, and six flavonoids from the water caltrop shells using a widely targeted metabolomics analysis. A natural deep eutectic solvent (NADES) was constructed based on L-proline and 1,4-butanediol, which maximized the extraction of polyphenolic and flavonoid compounds from the samples. An analytical method for the quantification of these bioactive substances was developed using UPLC-MS/MS technology. Based on this method, the contents of typical polyphenols and flavonoids in Trapa shells from different production areas in China were analyzed. The results of the quantitative analysis revealed that there were certain differences in the content of bioactive substances across samples from different regions. Samples from eastern production areas exhibited a richer content of bioactive substances, with higher levels of polyphenolic compounds compared to samples from other regions. • 12 typical Polyphenols and flavonoids are identified from water caltrop shells. • A NADES based on L-proline and 1,4-butanediol were optimized to maximize the extraction of polyphenols and flavonoids. • Quantitative analysis reveals that some bioactive compounds exhibit variations in concentration from different regions.