A Study on the Extraction, Fermentation Condition Optimization, and Antioxidant Activity Assessment of...

Kluyveromyces marxianus exhibits advantages such as strong thermotolerance, rapid growth rate, and high safety, making it an excellent host cell for the production of bio-based products. In this study, two exopolysaccharides, KE1 and KE2, were isolated from the fermentation broth of the strain K. marxianus KM-502, and their hydroxyl radical scavenging, DPPH scavenging, and Fe²⁺-reducing activities were evaluated. In vitro antioxidant assays demonstrated that exopolysaccharide KE2 exhibited superior antioxidant activity compared to KE1. The fermentation conditions were optimized using single-factor experiments followed by response surface methodology (RSM). The optimized fermentation process revealed that the most suitable fermentation medium consisted of 8% sucrose, 1.99% peptone, and 0.13% CaCl₂, while the optimal fermentation conditions were a medium volume of 74 mL in a 300 mL flask, pH 6.7, an inoculum size of 1.99%, a temperature of 30 °C, a shaking speed of 160 r/min, and a cultivation time of 96 h. After optimizing the fermentation conditions of K. marxianus KM-502, the exopolysaccharide (EPS) yield reached 5842.42 mg/L, representing a 22.77-fold increase compared to the yield before optimization. In summary, this study isolated exopolysaccharides KE1 and KE2 from K. marxianus KM-502. These exopolysaccharides demonstrated significant antioxidant activities, and the fermentation conditions for exopolysaccharide production were optimized. The findings of this study will facilitate the further development and utilization of exopolysaccharides from K. marxianus.