Effect of Frequent Broccoli Intake on Rat Gut Microbiota Metabolism and Composition

Abstract

The aim of this study is to investigate whether frequent cooked broccoli intake can modify the composition and metabolism of gut microbiota, specifically if broccoli feeding improves the ability of gut microbiota to hydrolyze glucoraphanin (termed myrosinase activity) and release bioactive sulforaphane. Myrosinase activity of cecal microbiota from adult male F344 rats fed with either 10% blanched, freeze‐dried (cooked) broccoli diet or control diet (AIN93G) was measured as the evaluation parameter. Results showed that feeding rats the broccoli diet for 4 days significantly increased myrosinase activity ex vivo compared with control diet (p<0.001). The stimulated myrosinase activity maintained those elevated levels when rats were fed the broccoli diet for longer periods (7 and 14 days). Remarkably, high‐throughput DNA sequencing data revealed a corresponding change in the gut microbiota composition based on microbial community analysis (MCA). The community composition of cecal microbiota from rats fed with the broccoli diet for 4, 7 and 14 days was clearly different from those fed for 0 and 1 day. To further identify which components in the broccoli diet that caused the change, a glucoraphanin‐free broccoli diet was made by hydrolyzing all the glucoraphanin to sulforaphane with exogenous myrosinase and was then fed to rats. Results showed cecal microbiota of rats fed with the whole broccoli diet exerted 4‐fold higher myrosinase activity than those rats fed the glucoraphanin‐free broccoli diets, indicating that it was the glucoraphanin in the broccoli, rather than sulforaphane, fiber or other components, that played the causative role of stimulation in the gut microbiota. Interestingly, the increased myrosinase activity was lost when the 4‐day broccoli diet was switched back to control diet for 3 days prior to harvest. Similar changes in glucoraphanin metabolic activity were observed using feces in place of cecal microbiota, indicating the potential for fecal metabolism to act as a biomarker of exposure. This study suggests that frequent ingestion of cooked broccoli may enhance the capability of gut microbiota to release the anti‐cancer bioactive sulforaphane from cooked broccoli.Support or Funding InformationUSDA/NIFA 2016‐67017‐24430