Insights into yeast cell disruption: Linking thermo-mechanical processing effects to physicochemical properties of yeast extract

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Various cell disruption methods exist, generating differently composed yeast extracts from Saccharomyces cerevisiae for food protein extraction. However, underlying mechanisms resulting in varying extract's physicochemical properties remain unclear. The objective of this study was to link these properties to thermo-mechanical and cell stress-induced processes. Five cell disruption methods (endogenous and exogenous enzymatic hydrolysis, ultrasonication, inline disperser, colloid mill) were implemented. Analyses were conducted regarding yeast cell morphology, yeast extract composition, and visual appearance. The endogenous enzymatic disruption resulted in the highest protein content of 65.0% ± 1.4%, as compared to the lowest content for colloid mill of 25.1% ± 0.3%. Moreover, yeasts were likely subjected to oxidative, and heat induced stress, especially during inline disperser and colloid mill disruptions. This was consistent with the highest contents of the stress osmolyte glycerol in these extracts (>70 g/kg), as opposed to the lowest content for ultrasonication (5.8 ± 0.1 g/kg). The elevated glycerol contents exerted a plasticizing effect on these two extracts. Furthermore, these two extracts depicted the lowest lightness (L-value <35). Precisely induced exposure to elevated temperatures and oxygen incorporation during disruption supported the proposed thermo-mechanical reactions, as Maillard reaction and oxidation, together with a significant negative correlation of glycerol and protein. Exposing the ultrasonicated suspension to elevated temperatures up to 95 °C reduced the protein content and L-value by 46% and 36%, respectively. The results revealed that elevated temperatures, and oxygen can mitigate protein content and visual appearance of Saccharomyces cerevisiae yeast extracts, which can impair application potential in foods.