Yeast-based biotechnology companies face an increasing challenge in deriving economic value from the byproducts generated through fermentative processes. Furthermore, growing environmental concerns are pushing companies toward adopting more sustainable and closed-loop economic systems, which aim to reduce waste production and find ways to valorize these byproducts. Spent yeasts obtained from fermentations represent an unused source of valuable bioactive compounds with potential applications across various industries, from food to pharmaceuticals. This PhD work focuses on the extraction, purification, and chemical modification of Saccharomyces cerevisiae glucans, complex polysaccharides composed of a mixture of α/β glycosidic linkages, to explore their biological properties related to skin health through in vitro assays and human skin ex vivo models. For this, the first stage of this thesis concentrated on developing a novel extraction and purification methodology to isolate glucans from two different S. cerevisiae strains: an engineered strain designed for biotechnology fermentation provided by Amyris and a wild strain produced in a lab-scale fermentation process. Two water-insoluble extracts were obtained, which displayed a high glucose purity and a similar chemical structure. Due to their water-insolubility, an extra chemical modification (carboxymethylation) was performed, resulting in two water-soluble extracts with new functional groups added to the polysaccharide chain. Once these extracts were obtained, comprising two water insoluble and two functionalized extracts, a safety assessment was conducted to ensure that glucans could be safely used as chemical ingredient for skin application. This assessment demonstrated that glucans had no genotoxic effect, no skin sensitization capacity, and no impact on the skin microbiota naturally present on healthy female skin. In the second stage of this study, both water-insoluble and carboxymethylated extracts were analyzed through in vitro assays to assess their biological properties for potential skin application. It was observed that glucans were capable of attenuating cytokine release (IL-1α/IL-6/IL-8) in a cell-induced inflammation model, using bacterial lipopolysaccharides (LPS) and pollution particle matter (PM), involving keratinocytes (HACAT) and macrophage-like THP-1 cells (mTHP-1). Using HACAT cells, it was also demonstrated that these extracts, with water-insoluble glucans showing a higher bioactive potential, effectively reduced intracellular reactive oxygen species (ROS) generation induced by PM and promoted cell migration in a wound healing assay. In the final stage of this thesis, all the extracts tested until now were individually incorporated into a cream formulation and applied in newly developed human skin ex vivo models to evaluate potential skin-related biological properties. Initially, all the creams containing glucans were applied to skin explants, and its permeability and impact on skin viability were assessed, with all the formulations showing no adverse effects on the skin tissue. It was also analyzed whether these formulated creams affected the presence of skin immune cells (Langerhans and M1/M2 macrophage cells) in the explants, and it was observed that some of the samples had the ability to modulate, either by increasing or reducing, the number of these cells present in the skin. After analyzing the skin’s structural components, it was also perceived that all cream formulations had the capacity to increase collagen deposition in the dermal layer, specifically collagen type-I. From a therapeutic perspective, it was demonstrated that the formulations tested had the capacity to reduce cytokine production (IL-1α/IL-6) when skin explants were exposed to SDS and PM, suggesting a potential application as an anti-inflammatory agent for topical use. Additionally, it was also shown that most of the cream formulations had the capacity to induce epidermal migration and wound closure, supporting the potential use of glucans as a wound repair agent. Overall, spent yeast glucans were demonstrated to be a safe and bioactive choice with various skin-related properties for potential skin application, noting that yeast glucans capacity is directly influenced by cell-to-cell interactions. Moreover, more studies are needed to explore the ways in which glucans can be applied to other skin-related areas, such as managing skin diseases like atopic dermatitis or combating skin viral infections like herpes simplex.
- Spent yeast valorization
- Sustainable biotechnology
- Glucans extraction
- Carboxymethylation
- Biological properties
- Skin health
- Skin application
- Doutoramento em Biotecnologia
Valorization of glucan extracts into a high-value bioactive ingredient
Sousa, P. M. C. (Student). 22 Jul 2024
Student thesis: Doctoral Thesis