| Abstract
| - The influence of hydrophobic polypeptides concentrated in beer foam, together with the compositionof iso-α acids and the content of malto-oligosaccharides in beer on foam stability, has beeninvestigated. The objective was to find out whether a shortage of one of these positive contributorsto foam stability could be compensated for by an increased presence of another or whether optimumlevels of each contributor is necessary. For that purpose, an image analysis method to evaluatebeer foam quality was developed. The foam collapse time was the parameter chosen to group beersaccording to their foam stability. Profiles of hydrophobic polypeptides that concentrate in beer foam,iso-α acids, and malto-oligosaccharides of 14 beer brands were acquired by high-performance liquidchromatography. Principal component analysis (PCA) was performed to show the relationship betweenbeer brands and its composition. Beers that contained propylene glycol alginate as a foam enhancershowed high foam stability except for one beer, which had a low content of hydrophobic polypeptides,thereby highlighting the requirement of threshold levels of hydrophobic polypeptides to obtain stablefoam. The data of samples that were devoid of a foam additive were subjected to a discriminantstatistical analysis. Foam stability declined in proportion to decreases in hydrophobic polypeptidesand to a lesser extent to decreases in iso-α-acid contents. Apparently, the content of malto-oligosaccharides were found to have no major influence on foam stability. The model of discriminateanalysis was found to explain 100% of the variance in data with 85.2% success in classifying allsamples according to the model, suggesting that foam stability is mainly governed by the beerconstituents evaluated in this study. Keywords: Beer; foam stability; hydrophobic polypeptides; iso-α acids; malto-oligosaccharides
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