Natural Strategies to Preserve Alcohol-Free Beer: Phenolamide Dimers with Anti-Yeast Potential

Trends in clean label food and the growing popularity of alcohol-free beers have led to a demand for natural compounds to prevent microbial spoilage. Oxidative coupling products of hydroxycinnamic acids and their amides, i.e. phenolamides, obtained via chemo-enzymatic synthesis and from barley rootlets, a beer brewing byproduct, were tested for their inhibitory activity against the beer spoilage yeast Saccharomyces cerevisiae subsp. diastaticus. Hydroxycinnamic acids, their dimers, and hydroxycinnamoylagmatines (HCAgms) did not inhibit the yeast. However, inhibitory activity was observed with HCAgm dimers. In particular, CouAgm-4-O-7′/3-8′-DCouAgm and FerAgm-4-O-7′/3-8′-DFerAgm were active at 46–255 μg/mL in beer. Notably, the newly synthesized agmatine amide of poacic acid, a stilbenoid dimer of ferulic acid, showed increased antiyeast activity compared to its monomeric precursors. These results demonstrate that amidation and oxidative coupling can increase the antiyeast activity of hydroxycinnamic acid derivatives, and that hydroxycinnamoylagmatine dimers possess potential as preservatives against wild yeast spoilage in beer.