Analysis of Glucosinolates and Phenolic Content in Sprouts of 7 Brassica rapa Subspecies

Objective: Brassica rapa is an important source of phytochemicals essential for plant defense and human health. To better understand their metabolic characteristics, this study aimed to investigate the glucosinolates and phenolic content from sprouts of 7 B. rapa subspecies. Methods: Glucosinolates and phenolic compounds were extracted using previously reported procedures, with slight modifications. Glucosinolates were identified based on their high-performance liquid chromatography peak area ratios and quantified based on the peak areas, retention time, and response factor and phenolic compounds were identified based on retention times and spiking tests and quantified concerning a corresponding calibration curve. Results: Statistical analysis showed that Choy sum (31.82 ± 2.3 mg/g DW) and Bok choy (31.73 ± 1.49 mg/g DW) presented the highest total glucosinolates content, and the lowest content was observed in Turnip rape (21.75 ± 1.67 mg/g DW). Between the contents of individual glucosinolates, progoitrin presented the highest content in Bok choy (17.84 ± 1.24 mg/g DW). The highest concentration of total phenolic compounds was found in the sprouts of Chinese cabbage (2.7 ± 0.05 mg/g DW), whereas the lowest concentration was found in Choy sum sprouts (2.17 ± 0.05 mg/g DW). The highest individual phenolic content was observed for benzoic acid (0.96 ± 0.03 mg/g DW) and rutin (0.85 ± 0.03 mg/g DW), which were highest in mizuna and Chinese cabbage, respectively. Conclusion: Subspecies may influence the levels of glucosinolates and polyphenols in vegetables. The results of our study showed the distinctive metabolic signatures embedded in the 7 B. rapa subspecies.