How Yeast Cells Process Oxidized Methionine in a Controlled Environment

Jenn Hoskins
19th August, 2024

How Yeast Cells Process Oxidized Methionine in a Controlled Environment

Image Source: Natural Science News, 2024

Key Findings

  • Researchers at Technische Universität Braunschweig studied how methionine oxidation affects beer flavor during brewing
  • Yeast can metabolize both free and peptide-bound forms of oxidized methionine (MetSO and MetSO2)
  • MetSO is mainly reduced back to methionine, minimizing the risk of off-flavor formation in beer
Protein oxidation in food systems has been a topic of increasing interest among food scientists due to its implications for food quality and human health. The oxidation of proteins can lead to changes in texture, flavor, and nutritional value of food products. A recent study conducted by researchers at Technische Universität Braunschweig has provided new insights into the role of methionine oxidation in the brewing process and its subsequent impact on flavor formation[1]. Methionine, an essential amino acid, is crucial in the brewing process as it can contribute to both desirable and off-flavors. During malting, a significant portion of methionine is oxidized to methionine sulfoxide (MetSO). The researchers hypothesized that MetSO and its further oxidized form, methionine sulfone (MetSO2), could be metabolized into volatile compounds during yeast fermentation, potentially affecting the flavor profile of beer. To test this hypothesis, they investigated whether the yeast Saccharomyces cerevisiae could catabolize these oxidized forms of methionine in both free and dipeptide-bound states. The study found that Saccharomyces cerevisiae was indeed capable of metabolizing both free and peptide-bound forms of MetSO and MetSO2. Notably, l-MetSO was degraded most rapidly when it was in its free amino acid form, whereas l-MetSO2 was degraded most quickly when bound in dipeptides. The researchers also observed different degradation behaviors for the (R) and (S) diastereoisomers of l-MetSO and l-methionine sulfoximine, indicating that the stereochemistry of these compounds plays a role in their metabolism. One of the significant findings of the study was the identification of methionol as the only metabolite of MetSO, with no formation of methionol sulfoxide. In contrast, MetSO2 was not converted to methionol or methionol sulfone but rather to the corresponding α-hydroxy acid. This suggests that the reduction of MetSO back to methionine occurs faster than its transamination, a process where an amino group is transferred to a keto acid to form new amino acids. These findings contribute to a more comprehensive understanding of protein oxidation in food systems, particularly in brewing. Previous research has highlighted the importance of protein oxidation in food deterioration and its potential health implications. For instance, food protein oxidation can occur throughout the entire processing axis, from primary production to intestinal digestion[2]. Additionally, protein oxidation in living tissues is known to play a crucial role in the pathogenesis of degenerative diseases, and its impact on food systems has only recently garnered attention[3]. The accumulation of lipid and protein oxidation products during food processing and storage poses potential cytotoxic and mutagenic risks to the gastrointestinal tract and internal organs[4]. The current study builds on these earlier findings by providing specific insights into the role of methionine oxidation in brewing. The researchers demonstrated that the presence of MetSO or MetSO2 in brewing malt does not lead to the formation of new, unknown volatile metabolites through the Ehrlich pathway, a metabolic route in yeast that converts amino acids to fusel alcohols and acids. This is an important finding as it suggests that the reduction of MetSO to methionine is a dominant pathway, minimizing the risk of off-flavor formation from these oxidized compounds. In conclusion, the study conducted by Technische Universität Braunschweig offers valuable insights into the metabolism of oxidized methionine forms during yeast fermentation in brewing. By elucidating the metabolic pathways and degradation behaviors of MetSO and MetSO2, the research provides a clearer understanding of how methionine oxidation impacts flavor formation in beer. These findings not only enhance our knowledge of protein oxidation in food systems but also pave the way for developing strategies to manage and control flavor profiles in brewing and other food processing applications.

GeneticsBiochemMycology

References

Main Study

1) Metabolization of Free and Peptide-Bound Oxidized Methionine Derivatives by Saccharomyces cerevisiae in a Model System.

Published 19th August, 2024

https://doi.org/10.1021/acs.jafc.4c05151

Related Studies

2) The Chemistry of Protein Oxidation in Food.

https://doi.org/10.1002/anie.201814144

3) Protein oxidation in muscle foods: a review.

https://doi.org/10.1002/mnfr.201000453

4) Dietary protein oxidation: A silent threat to human health?

https://doi.org/10.1080/10408398.2016.1165182


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