Effect of polyphenols on saccharomyces cerevisiae fed-batch fermentation

Student thesis: Doctoral Thesis

Abstract

The industrial production of β-farnesene is traditionally achieved through Saccharomyces cerevisiae fed-batch fermentation, often employing sugarcane syrup as the feedstock. However, the presence of phenolic compounds in sugarcane syrup potentially impacts yeast performance. This thesis aimed to study the evolution of phenolic compounds over β-farnesene production by S. cerevisiae in bioreactor fermentations with sugarcane syrup, assess the phenolic compounds’ impact on this process, and explore the potential of beet syrup, a lower phenolic content alternative feedstock, for β-farnesene production via a similar fermentation process. The phenolic compounds present within both the sugarcane syrup and the fermentation broth were systematically identified and quantified. Sugarcane syrup presented 50.7 mg/L of total phenolic content (TPC), comprising hydroxybenzoic acids, hydroxycinnamic acids and flavonoids. Among two kinetic models assessed, the Weibull model exhibited superior fitting capacity (R2 ≥ 0.85) and accurately depicted phenolic compounds’ accumulation during the 13-day fed-batch fermentation in 2 L bioreactors. The concentration of most phenolic compounds ascended until day three, stabilizing until the end of the fermentation process. Nevertheless, hydroxybenzaldehyde and protocatechuic, caffeic, ferulic and p-coumaric acids declined after the second day, indicating yeast metabolism. This work provides a model that can be applied to describe the phenolic accumulation during similar fed-batch processes. To investigate the phenolic influence on the fermentation, sugarcane syrup phenolic compounds were effectively removed with activated charcoal. The syrup purification process was optimized with a central composite design, varying the type of charcoal, concentration of charcoal and contact time. Optimization yielded purification conditions with charcoal pellets at 115 g/L and 12.5 h of contact time, while removing 96.7 % of phenolic compounds and recovering 43.7% of syrup mass. Purified syrup introduction into fermentations displayed divergent scale-dependent outcomes. Although in shake-flasks there was an 11 % enhancement in β-farnesene productivity, no significant increase was detected in bioreactors. In contrast, an increment in biomass productivity was exclusive to bioreactors, registering an increase of 12 %. Therefore, for the conditions tested, the phenolic compounds did not influence the β-farnesene production at large-scale. Moreover, β-farnesene production using an alternative feedstock, sugarbeet syrup, was successful. Despite presenting lower TPC (21.3 mg/L) compared to sugarcane syrup (50.7 mg/L), beet syrup contained high glucose (193 g/L) and hydroxymethylfurfural (HMF; 1.4 g/L) concentrations. Inoculum production in the second bioreactor step required optimization due to slow growth and the desired cell density was achieved with a fed-batch mode with initial 40 g/L of sugars from beet syrup and 10 g/L of sugar pulses. Over 8 days, fed-batch fermentation yielded 127 g/L β-farnesene concentration, with 19.44 % cumulative yield and 1.70 g/L/h cumulative productivity, affirming the viability of using beet syrup as the fermentation feedstock. In conclusion, this thesis showcased the dynamic relationship between phenolic content and β-farnesene fed-batch process highlighting an increase in the fermentation broth's phenolic content. Notably, specific phenolic compounds were metabolized by the yeast. The effects of sugarcane syrup phenolic compounds on S. cerevisiae were dependent on the fermentation scale. While valuable for mitigating yeast oxidative stress, phenolic compounds’ removal did not enhance bioreactor fermentation productivity. On the other hand, the utilization of beet syrup as feedstock may enable β-farnesene production in mild climates without extensive sugarcane cultivation, fostering sustainable production across diverse regions.
Date of Award26 Jan 2024
Original languageEnglish
Awarding Institution
  • Universidade Católica Portuguesa
SupervisorCarla Oliveira (Supervisor), Ana Lúcia Silva Oliveira (Co-Supervisor) & Erdem Çarsanba (Co-Supervisor)

Keywords

  • Saccharomyces cerevisiae
  • Phenolic compounds
  • β-farnesene
  • Bioreactor fermentation
  • Antioxidant and antimicrobial activities
  • Sugarcane syrup
  • Sugarbeet syrup

Designation

  • Doutoramento em Biotecnologia

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