Reference Number: 167
Yeast: Saccharomyces cerevisiae
The consumers of today have an increasing interest in high quality bread with appealing aroma. The scope of this work is to investigate how aroma in wheat bread crumb is influenced by different fermentation conditions: amount of yeast (20, 40 and 60 g/kg flour) and fermentation temperature (5, 15 and 35 C). Dough samples were fermented to equal height and baked, and the aroma compounds from the bread were extracted by dynamic headspace extraction and analyzed by gas chromatography and mass spectrometry. Quantification of the aroma compounds was performed by multiple headspace extraction. The most aroma active compounds identified were 3-methylbutanal, (E)-2-nonenal, 3-methyl-1-butanol, and 2,3-butanedione. Increasing the yeast concentration was found to increase formation of the majority of the compounds formed from the yeast metabolism, with 2,3-butanedione and phenylacetaldehyde as the most aroma active compounds. High fermentation temperature (15 and 35 C) increased formation of many lipid oxidation compounds, with hexanal and heptanal having the highest odour activity values. Low fermentation temperature (5 C) was found to increase formation of the three esters ethyl acetate, ethyl hexanoate, and ethyl octanoate, with ethyl hexanoate having the highest odour activity value. The odour activity values of the esters were generally low.
SIGNIFICANCE OF THIS STUDY
The current paper mainly focusses on the contribution of yeast to the flavour and aroma of bread. The paper states that the aroma compounds identified in fermented bread crumb are mainly derived from the metabolism of yeast and from the oxidation of flour lipids, whereas the aroma compounds in the crust originates from Maillard reactions occurring at high temperatures and low water activity between reducing sugars and amino acids. The influence of fermentation temperature on the crumb aroma was investigated for the two fermentation products 3-methyl-1-butanol and 2-phenylethanol. The study found that with yeast fermentation, a total of 46 aroma compounds were identified in the bread crumb from the nine different fermented breads. The authors found that the identified aroma compounds were formed mainly from the metabolism of yeast during fermentation which included iso- alcohols, 3-methylbutanal, phenylacetaldehyde, 2,3-butanedione (diacetyl), 3-hydroxy-2-butanone, esters and acids and from oxidation of flour lipids resulting in aldehydes, ketones and 2-pentylfuran). When they checked if the concentration of Yeast had an effect on the amounts of these volatile compounds, they found a clear positive effect of yeast concentration on the production of the majority of aroma compounds formed from the fermentative activity of yeast such as 2-methyl-1-propanol (Ethereal, Winey, Alcohol), 2-phenylethanol (floral, Fade rose, Rose, Rose water, Honey), phenylacetaldehyde (Green, Sweet, Floral, Hyancinth, Cocoa, Fatty, Waxy), 2,3-butanedione (Phenol, Plastic, Rubber) and ethyl 3-methylbutanoate (Roasted, Wine, Onion, Fruity).