The quality characteristics of Oenothera biennis juice (OJ) fermented with various concentrations of sugar solutions (50, 60, and 70캛rix) and at different temperatures (20 and 30캜) were investigated. The sugar concentration and pH of fermented OJ decreased during fermentation and more rapidly decreased at 30캜 rather than at 20캜. The number of total bacteria increased during 6 days of fermentation and decreased gradually thereafter, and coliform bacteria were not detected after 8 to 10 days of fermentation at 20 and 30캜. Enzyme activities (invertase, amylase, and cellulase) of fermented OJ with 50캛rix sugar solution were the highest among the different treatments after fermentation for 4 days at 30캜. Total polyphenol content and DPPH radical scavenging ability increased during fermentation. The highest total polyphenol contents and DPPH radical scavenging ability were 7.1 mg TAE/mL and 58.6%, respectively, when fermented at 30캜 with 50캛rix sugar solution.

Keywords: Oenothera biennis, quality characteristics, fermentation, phenolic compounds, antioxidant activity