Exploiting the diversity in spent yeast for its valorisation towards producing yeast-derived processing aids

Abstract

In view of sustainability and zero-waste initiatives, the valorisation of sidestreams is a key emerging topic in the wine industry. Spent yeast (SY), usually found in the fermentation lees, is the second largest sidestream in wineries, accounting for approximately 25% of the total sidestreams, amounting to approximately 2.5 million tonnes worldwide^1,2. Today, SY is mainly either processed as waste, which is associated with a high cost, or used for low-value applications such as bioenergy or compost^1,3. However, several high-value applications are on the rise where specific yeast-derived components are used for functional purposes in food or feed. Within the wine industry, several of these yeast-derived products are already used to improve wine quality. For example, mannoprotein isolates can be used to protect against tartrate precipitations or protein haze and to accelerate the effects on on-lees ageing^1,4. However, these products are usually derived from baker’s yeast instead of using the spent yeast already available. To accommodate the use of SY for such high-value applications, it is important to understand yeast properties to allow for an efficient production of these yeast-derived components. Therefore, we set out to investigate the effect of fermentation on yeast by examining a wide variety of SY samples to evaluate their potential for valorisation towards functional yeast-derived components.

To achieve this, 32 spent yeast samples were collected from various wineries and breweries. These samples were analysed for a set of chemical (e.g. cell wall composition, protein content, polyphenol content) and physiological characteristics (e.g. cell size, cell wall hydrophobicity, cell surface charge). In these samples, a large variability in cell wall compounds (β-glucan 7-18% and mannoprotein 6-23%) was observed. To investigate the impact of this variability on the isolation of yeast-derived components, SY was autolysed and the amount of cell wall material in the isolates was determined, which varied between 22 and 87%. In addition, the assimilable nitrogen content in yeast extracts varied by a factor of 5 depending on the specific SY sample. Results from this work can be used to assess the suitability of an SY stream for valorisation purposes, which will increase the value of these streams and provide winemakers with an additional stream of revenue.

References

[1] De Iseppi, A., Lomolino, G., Marangon, M., & Curioni, A. (2020). Current and future strategies for wine yeast lees valorization. Food Research International, 137, 109352.

[2] OIV (2024) State of the world vine and wine sector in 2023. International Organisation of Vine and Wine http://www.oiv.int/sites/default/files/2024-04/OIV_STATE_OF_THE_WORLD_VINE_AND_WINE_SECTOR_IN_2023.pdf

[3] Devesa-Rey, R., Vecino, X., Varela-Alende, J. L., Barral, M. T., Cruz, J. M., & Moldes, A. B. (2011). Valorization of winery waste vs. the costs of not recycling. Waste management, 31(11), 2327-2335.

[4] Valentin, D., Chollet, S., Nestrud, M., Abdi, H. (2018). Descriptive analysis in sensory evaluation, 535-559.