Abstract
Flavor instability of beer is affected by the rise of aroma-active aldehydes during aging. Aldehydes can be either released from bound-state forms or formed de novo. This second part of our study focused on the de novo formation of aldehydes during the Maillard reaction, Strecker degradation, and oxidation reactions. Key precursor compounds for de novo pathways are free amino acids. This study varied the potential for reactions by varying free amino acid content in fresh beer using different proteolytic malt modification levels (569–731 mg/100 g d. m. of soluble nitrogen) of the used malt in brewing trials. Overall, six pale lager beers were produced from three malts (different malt modification levels), each was made from two different barley varieties and was naturally and forcibly aged. It was found that higher malt modification levels in fresh beer and during beer aging increased amino acid and dicarbonyl concentrations as aging precursors and Strecker aldehyde contents as aging indicators. Dicarbonyls were degraded during aging. Advanced glycation end products as possible degradation products showed no consistent formation during aging. Therefore, Strecker reactions were favored during beer aging. No alternative oxidative formation of Strecker aldehydes from their corresponding alcohols could be confirmed. Along with the preceding part one of our investigation, the results of this study showed that de novo formation and release occur simultaneously. After 4 months of natural aging, aldehyde rise is mainly accounted for by de novo formation.
Highlights
IntroductionBeer flavor is affected by various chemical reactions, leading to flavor instability
After bottling, beer flavor is affected by various chemical reactions, leading to flavor instability
Since the preceding study observed the release of aging-relevant aldehydes, this study focused on de novo formation pathways
Summary
Beer flavor is affected by various chemical reactions, leading to flavor instability. One main reason for a change in flavor in beers is the rise of aging indicators such as sensory-active aldehydes. In our preceding study (part one), the sensory and chemical effects of beer aging in lager beer were introduced [1]. The concentration of agingrelevant aldehydes increases during storage, and these aldehydes can be either formed by their release from bound-state aldehydes forms or by de novo formation pathways [2]. The preceding study focused on the release of bound-state aldehydes (part one). Important reactions for de novo formation of aging aldehydes are the Strecker degradation, the Maillard reaction, and oxidation reactions such as lipid oxidation or oxidation of the corresponding alcohols [3,4]
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