Valorization of yeast-based mannans as sources of bioactive ingredients for nutraceutical applications

Student thesis: Doctoral Thesis


Amyris, Inc., a company dedicated to synthetic biotechnology, seeks to minimize the environmental impact of its industrial processes. Accordingly, the work hereby presented focuses on the valorization of their yeast by-products (Saccharomyces cerevisiae) to obtain bioactive compounds such as mannans and mannan oligosaccharides (MOS) for various applications in food, animal feed, and nutraceutical industries. To extract mannans from yeast biomass, different extraction processes (physical, chemical, and enzymatic) were explored, and final products were thoroughly characterized regarding their structural, physicochemical, and biological properties. Enzymatic hydrolysis provided the highest solid yield but was costly. Alkaline hydrolysis with 0.25 M sodium hydroxide resulted in a higher mannan yield but presented salt contamination issues. Thermal hydrolysis with water was chosen as the preferred method due to its favourable characteristics, including a high mannan content and minimal associated costs. The next step aimed at the production of MOS from the extracted mannans using two methodologies: hydrothermal production in a Parr reactor (MOS Parr), and hydrolysis using phosphoric acid (MOS H3PO4). In addition to their structural and physicochemical characterization, the produced MOS were also evaluated for their biological potential. Among the former properties, the hydrothermal extract showed higher molecular weight populations of oligomers. Both extracts were subjected to a simulation of the gastrointestinal tract digestion, and their immunomodulatory responses were assessed. Besides not showing anti-inflammatory properties, the extracts acted as immunostimulants by increasing the expression levels of the interleukin 6 (IL-6), a pleiotropic cytokine that plays a central role in the immune response. Regarding their potential applications, the MOS extracts were evaluated for their ability to inhibit the adhesion of uropathogenic Escherichia coli (UPEC) to bladder cells, aiming to prevent urinary tract infections (UTIs). Both extracts were assessed in prophylaxis and competition mode assays, showing a significant inhibition of UPEC in the competition assay (MOS H3PO4 89.6 ± 1.4% and MOS Parr 79.8 ± 1.1%) when compared to D-mannose, one of the commercial benchmarks most widely used in non-antibiotic UPEC therapies. Additionally, the extracts showed potential to be used in the management of vulvovaginal candidiasis (VVC). When in simulated vaginal fluid (SVF), and although a small decrease in Candida albicans growth was observed only in prophylaxis assays, both extracts promoted lactobacilli growth (a 4 log cycles increase in cell viability). Furthermore, in vitro competition studies demonstrated that MOS Parr extract, in combination with Lactobacillus crispatus, effectively inhibited the adhesion of C. albicans to vaginal cells (adhesion reduction of ~69%), while prophylactic evaluation revealed that both extracts, in synergy with the population of L. crispatus, effectively prevented the adhesion of C. albicans (adhesion reduction of ~56% and ~60% for MOS H3PO4 and MOS Parr, respectively). Furthermore, the chemical modification of mannans through carboxymethylation was investigated to enhance their biological potential. Carboxymethylation affected the composition, physical appearance, and antioxidant capacity of mannans, and the modified mannans demonstrated increased efficacy in inhibiting the growth of pathogenic bacteria and fungi, namely UPEC and C. albicans. Overall, this dissertation contributes to the broader objective of valorizing yeast by-products and harnessing their bioactive compounds for applications in food and nutraceutical industries, while providing the basis for the development of mannans and MOS supplements for the management of specific health-related challenges associated with UPEC and Candida albicans.
Date of Award21 Dec 2023
Original languageEnglish
Awarding Institution
  • Universidade Católica Portuguesa
SupervisorAna Carvalho (Supervisor), Carla F. Pereira (Co-Supervisor) & Joana Raquel de Oliveira Durão (Co-Supervisor)


  • Mannans extracts
  • Mannan oligosaccharides extracts
  • Characterization
  • Inhibition of uropathogens adhesion
  • Carboxymethylation of mannans


  • Doutoramento em Biotecnologia

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