Development of peptide-rich extracts from yeast by-products for nutraceutical application

Abstract

Over the years, synthetic biology has grown through the use of engineered yeasts for sustainable ingredients production. Similar to the brewing industry, a considerable amount of spent yeast has been generated, which holds a significant nutritional value as an alternative protein source. Considering the increase of global population and the consequent rise in protein demand, this thesis aims to valorise peptides from engineered yeast by producing peptide-rich extracts. These extracts are derived either directly from yeast or from the waste residues of β-glucan and mannan extractions (yeast cell wall components), following a circular economy approach to be applied to nutraceutical industry. For the direct extraction of peptides from yeast, scalable and sustainable methodologies such as high-pressure homogenization, sonication, enzymatic hydrolysis, and autolysis were employed. Engineered yeast extracts exhibited excellent nutritional profiles, similar to wild-type. Autolysis emerged as a promising approach, although additional sustainability metrics need to be studied for the industrial implementation of this process. To further explore the biological properties of autolysate peptides, two purification methods were applied: ultrafiltration and size exclusion chromatography. The resulting fractions displayed diverse protein content, molecular weight distributions and peptide sequences, demonstrating high angiotensin-converting enzyme inhibition capacity, antioxidant activity, and greater inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase than the original autolysate. This suggests the importance of purification in producing a cholesterol-reducing dietary supplement with these properties. To best of our knowledge, this thesis reports the first demonstration of yeast peptide associated HMG-CoA reductase inhibition. Considering cost-effectiveness, ultrafiltration appears to be the most suitable method for producing peptide-rich extracts for the nutraceutical market. Ultrafiltration was also applied to the supernatants of β-glucan and mannan extraction residues, maximizing the circular economy approach for peptide-rich extract production. These extracts exhibited similar nutritional and bioactive performance to those directly obtained from yeast, making them excellent ingredients for the nutraceutical sector. Considering the amino acid composition within the peptide extracts, the production of Fe-peptide complexes was studied and the complexes produced with Gpep > 1 kDa fraction (peptide fraction with molecular weight higher than 1 kDa derived from β-glucan extraction residues) under anoxic conditions were identified as the most adequate. From the applied factorial design, the reaction conditions were optimized (pH 6.0 for 30 min), and complexation was confirmed through chemical and structural analysis. Finally, the complexes were subjected to an in vitro simulation of human gastrointestinal tract, and Fe absorption was analysed using a human colon adenocarcinoma cell line. The results revealed that the complexes behaved similarly to Fe salts and commercial Fe bisglycinate, indicating their promising potential for dietary Fe supplementation. Additionally, the peptides from the complexes demonstrated antioxidant activity, suggesting protection of Fe against oxidation in different gastrointestinal environments. In summary, this thesis promotes the valorisation of spent engineered yeast, exploring the production of peptides extracts directly from biomass or from residues arising from other components extraction. Indeed, this production can represent an alternative food source and/or dietary supplements for managing anaemia, as well as providing peptide extracts for several other areas such as cosmetics or ingredients for microorganisms’ fermentation.

Date of Award	23 Feb 2024
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Ana Paula Taboada da Costa Santos Carvalho (Supervisor), Carlos Ferreira (Co-Supervisor) & Joana Odila Mendes de Sá Pereira (Co-Supervisor)