Date of Graduation


Document Type


Degree Name

Master of Science in Food Science (MS)

Degree Level



Food Science


Sun-Ok Lee

Committee Member

Zhao, Jiangchao

Second Committee Member

Lafontaine, Scott


Bioactive compounds, Gut microbiota, Nutrition, Onion peel, Polyphenols


Obesity, a pervasive global health concern, involves a complex interplay between genetic factors, dietary patterns, and the gut microbiota. Onion peels are rich in polyphenols and known for their antioxidant properties. However, the effects of in-vitro digested onion peel extract has not been investigated thus far. This study therefore assesses the effects of digested bioactive compounds from onion peels, emphasizing gut microbiota shift and metabolites. Onion peel extract (OPE), digested onion peel extract (DOPE), and solid-phase-extracted digested onion peel extracts (SPE-DOPE) were analyzed for total phenolic content (TPC) and antioxidant activity. SPE-DOPE exhibited the highest TPC and antioxidant activity. Fecal samples from 16 obese adults were fermented using four treatments: control (CONT), fructooligosaccharide (FOS), SPE-DOPE, and FOS+SPE-DOPE. Sampling at time 0 to 24 hours revealed that SPE-DOPE treatment resulted in the highest total SCFA production, followed by FOS + SPE-DOPE and FOS. SPE-DOPE increased acetic and propionic acid but not butyric acid. At phylum level microbial changes, treatments with SPE-DOPE, and FOS + SPE-DOPE led to significant decreases in Firmicutes at 24-hours compared to 0 hour. At 24 hour, significantly higher Proteobacteria was observed in females compared to males while Verrucomicrobiota was significantly increased in males compared to females. At genus level, FOS, SPE-DOPE and FOS+SPE-DOPE significantly increased Enterobacteriaceae from 0 hour to 24 hour. The findings suggest that taking onion peel bioactive compounds may have positive effects by increasing SCFA and modulating gut microbiota in obesity.

Available for download on Thursday, February 13, 2025