Abstract
The relationship between the chemical structure of model substances (fatty acids, monoacylglycerols, and fatty alcohols) and gushing development and suppression was elucidated. Gushing increased with increasing aliphatic chain length, beginning with a minimum length. Mono- and polyunsaturated cis-fatty acids such as oleic acid (C18:1), linoleic acid (C18:2), linolenic acid (C18:3), and arachidonic acid (C20:4) were identified as gushing-negative. These unsaturated fatty acids completely suppressed gushing, which was induced by palmitic acid and malt extract. The trans-isomer of oleic acid (C18:1), the trans-fatty acid elaidic acid (C18:1), which is unsaturated but nearly linear, could not suppress gushing and actually caused it. The results showed that the gushing-suppressing effect of unsaturated cis-fatty acids (C18 and C20) resulted from the physical orientation of the bend(s) in the aliphatic chain. In contrast to the other unsaturated cis-fatty acids, the monounsaturated cis-fatty acid nervonic acid (C24:1) did cause gushing. This was explained by the fact that the rectilinear aliphatic chain (from the head group to the fifteenth C atom) was long enough to enable intensive hydrophobic interaction, which allowed close agglomeration of the compounds. In this context, the melting point proved to be an interesting physicochemical parameter for gushing: all examined fatty substances with a melting point higher than approx. 40°C caused gushing. The model substances were successfully applied to find new and more complex gushing structures. A new amino acid sequence (NH2-Ile-Ile-Ile-Ile-Ile-Asp-Asp-COOH) was chosen to synthesize a peptide that caused distinct overfoaming. Gushing caused by this peptide was completely prevented by linoleic acid. The results of this study demonstrate that the model substances tested could be helpful in the identification of well-known substances in beer and beverages for research into their gushing characteristics.
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