Factors affecting Strecker aldehyde levels in alcoholic fermentation

Abstract

Strecker aldehydes (SAs) are volatile compounds that significantly influence wine aroma and quality, contributing notes such as “cooked vegetable” (methional), “honey” (phenylacetaldehyde), and “malt” (2-methylpropanal, 2-methylbutanal, 3-methylbutanal). Although traditionally linked to oxidative faults, recent evidence suggests that alcoholic fermentation itself can be a relevant source of SAs [1]. During fermentation, amino acids are metabolized via the Ehrlich pathway, generating aldehyde intermediates that are usually reduced to alcohols. However, incomplete reduction can occur [2-3], particularly in the presence of sulfite or polyphenols [4], leading to residual SAs that may bind SO₂ as reversible adducts, potentially affecting aroma during aging [5]. This study evaluates the formation and accumulation of SAs under different fermentation conditions through five independent experiments. Three experiments used synthetic musts to investigate the effects of yeast strain, Zn²⁺ concentration, and SO₂ levels. A fourth experiment examined SO₂ interactions in polyphenol-enriched media, while the fifth monitored SAs in industrial fermentations. Results confirm that SAs are naturally produced during alcoholic fermentation and are predominantly present as SO₂-bound adducts. Their accumulation strongly depends on yeast-mediated sulfite metabolism and the availability of SO₂ during the Ehrlich pathway. Temporal formation patterns varied by compound and batch: 2-methylbutanal was produced in parallel with SO₂ and hence acetaldehyde, whereas phenylacetaldehyde and methional formed earlier. Methional accumulation also showed strain-specific differences. Although yeast strain strongly influenced SO₂ metabolism and aldehyde quenching, final concentrations of most SAs were only weakly strain-dependent, and the impact of added SO₂ varied by compound, being negligible for methional. These findings demonstrate that wine shelf life may already be compromised during alcoholic fermentation, as shown by analyses in real musts and wines, and highlight the need to restructure fermentation practices to minimize Strecker aldehyde formation.

References

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