IRC7 AND VOLATILE THIOLS IN BEER

An indirect enzymatic assay was performed to evaluate the actual activity of β-lyase. In this assay, the initial compound is transformed by β-lyase and, through a secondary reaction, a measurable change over time is generated. This change is detected by spectrophotometry, by monitoring absorbance variation at a specific wavelength. The greater the change in absorbance, the higher the enzymatic activity. 

This “in vitro” assay simulates what occurs during fermentation. And allows a reliable estimation of how effectively a yeast strain can release fruity and tropical aromas from initially non-aromatic compounds.

The results show that most Saccharomyces cerevisiae ale brewing strains possess the functional form of the gene (IRC7L). However, the presence of this allele alone does not fully explain the observed enzymatic activity or the resulting aromatic profile. The results highlight the complexity of the relationship between genotype and phenotype, showing that genetic characteristics, gene expression, enzyme activity and substrate availability can all contribute to the final aromatic outcome. In particular, the alleles and the substrate on which the enzyme acts are key factors in determining aroma intensity.

How to read the table: while β-lyase activity alone does not fully determine the final aromatic profile, the classification below provides a useful reference for comparing the thiol-release potential of different brewing strains.