Abstract
Understanding how the dough fermentation conditions influence the wheat bread production time and the bread aroma is important for the bread industry. The overall purpose of this PhD project is to investigate the effects of commercial baker’s yeast (level and type) and fermentation temperature on dough expansion and aroma in bread crumb.
In Paper I the effects of commercial baker’s yeast (level and type) and fermentation temperature on dough expansion were investigated. Wheat doughs were fermented by seven commercial baker’s yeasts (baker’s yeast I to VII) at different yeast concentrations (2.88•1014, 5.76•1014 and 8.64• 1014 CFU/kg flour, corresponding to 20-40, 40-80 and 60-120 g/kg flour) and fermentation temperatures (5, 15, 25
and 35°C). Dough expansion was investigated by monitoring the dough height and the expansion profile was found to be described well by a first order kinetic model. The highest kinetic rate constants corresponding to the shortest fermentation times were found for doughs fermented at 25°C and the highest yeast concentration. Doughs fermented with commercial baker’s yeast I, II, III and V had shorter fermentation times compared to fermentation with baker’s yeast IV, VI and VII. The longest
fermentation times were generally found for doughs fermented with all baker’s yeasts at 5°C and the lowest yeast concentration (2.88•1014 CFU/kg flour).
In Paper II, III and V wheat breads were produced for volatile analysis. The dough samples were fermented to equal height and baked and the volatile compounds from the bread crumb were extracted by dynamic headspace sampling and analysed by gas chromatography mass spectrometry. A wide range of volatile compounds was identified in bread crumb, mainly originating from the activity of yeast and from oxidation of flour lipids. The dominating fermentation compounds were alcohols, aldehydes as well as 2,3-butanedione (diacetyl), 3-hydroxy-2-butanone (acetoin), esters and acids. Furthermore, oxidation of flour lipids was generating primarily aldehydes and ketones.
Quantification of the volatile compounds in bread crumb was performed by multiple headspace extraction (Paper II, III and V). The compounds were evaluated according to their odour activity value (OAV). The most aroma active compounds (OAV > 6) identified in bread crumb were; (E)-2-nonanal (green, tallow), 3-methylbutanal (malty), 3-methyl-1-butanol (balsamic, alcoholic), nonanal (citrus),
hexanal (green), 2,3-butanedione (buttery, caramel), 1-octen-3-ol (mushroom) and phenylacetaldehyde (honey-like). Esters were also identified in bread crumb (e.g. ethyl acetate, ethyl hexanoate and ethyl octanoate) and they are of interest because of their fruity and pleasant odours, however the OAV’s of the esters were generally low (0.1 to 0.5).
In Paper II the effects of yeast level (20, 40 and 60 g baker’s yeast VII/kg flour) and fermentation temperature (5, 15 and 35ºC) on aroma in bread crumb were investigated. Fermentation with the highest yeast concentration (60 g/kg flour) resulted in bread containing the highest concentration of the majority of the compounds formed from yeast activity (e.g. 2,3-butanedione and phenylacetaldehyde), compared to doughs fermented at lower yeast concentrations (20 and 40 g/kg flour). A fermentation temIII perature at 5°C resulted in breads with the highest concentration of the three esters; ethyl acetate, ethyl hexanoate and ethyl octanoate, compared to breads fermented at higher temperatures (15 and 35°C). Fermentation at 15 and 35°C resulted in breads with the highest concentration of many lipid oxidation compounds (e.g. heptanal and hexanal) compared to breads fermented at 5°C.
In Paper III the effect of the type of commercial baker’s yeast (baker’s yeast I to VII, 2.88•1014 yeast CFU/kg flour) on bread aroma was investigated. Breads fermented by commercial baker’s yeast I to IV had the significantly highest concentration of 2,3-butanedione and 1-propanol compared to breads fermented by the other yeasts. Furthermore, 3-methylbutanal, 2-methyl-1-propanol and ethyl acetate were
found in significantly highest concentration in breads fermented by baker’s yeast I and II. Phenylacetaldehyde and 2-phenylethanol were found in the significantly highest concentration in breads fermented by baker’s yeast V and VI. The fact that dough fermentation time and bread aroma was significantly influenced by the type of commercial yeast indicates that some of the seven baker´s yeasts might differentiate in yeast strain.
Commercial baker’s yeast (level and type) and fermentation temperature are concluded to significantly influence the fermentation time and the aroma profile of bread crumb. Sensory analysis and analysis of acids and non-volatile compounds in breads fermented by the same conditions as in this PhD thesis could be relevant in future research studies.
In Paper I the effects of commercial baker’s yeast (level and type) and fermentation temperature on dough expansion were investigated. Wheat doughs were fermented by seven commercial baker’s yeasts (baker’s yeast I to VII) at different yeast concentrations (2.88•1014, 5.76•1014 and 8.64• 1014 CFU/kg flour, corresponding to 20-40, 40-80 and 60-120 g/kg flour) and fermentation temperatures (5, 15, 25
and 35°C). Dough expansion was investigated by monitoring the dough height and the expansion profile was found to be described well by a first order kinetic model. The highest kinetic rate constants corresponding to the shortest fermentation times were found for doughs fermented at 25°C and the highest yeast concentration. Doughs fermented with commercial baker’s yeast I, II, III and V had shorter fermentation times compared to fermentation with baker’s yeast IV, VI and VII. The longest
fermentation times were generally found for doughs fermented with all baker’s yeasts at 5°C and the lowest yeast concentration (2.88•1014 CFU/kg flour).
In Paper II, III and V wheat breads were produced for volatile analysis. The dough samples were fermented to equal height and baked and the volatile compounds from the bread crumb were extracted by dynamic headspace sampling and analysed by gas chromatography mass spectrometry. A wide range of volatile compounds was identified in bread crumb, mainly originating from the activity of yeast and from oxidation of flour lipids. The dominating fermentation compounds were alcohols, aldehydes as well as 2,3-butanedione (diacetyl), 3-hydroxy-2-butanone (acetoin), esters and acids. Furthermore, oxidation of flour lipids was generating primarily aldehydes and ketones.
Quantification of the volatile compounds in bread crumb was performed by multiple headspace extraction (Paper II, III and V). The compounds were evaluated according to their odour activity value (OAV). The most aroma active compounds (OAV > 6) identified in bread crumb were; (E)-2-nonanal (green, tallow), 3-methylbutanal (malty), 3-methyl-1-butanol (balsamic, alcoholic), nonanal (citrus),
hexanal (green), 2,3-butanedione (buttery, caramel), 1-octen-3-ol (mushroom) and phenylacetaldehyde (honey-like). Esters were also identified in bread crumb (e.g. ethyl acetate, ethyl hexanoate and ethyl octanoate) and they are of interest because of their fruity and pleasant odours, however the OAV’s of the esters were generally low (0.1 to 0.5).
In Paper II the effects of yeast level (20, 40 and 60 g baker’s yeast VII/kg flour) and fermentation temperature (5, 15 and 35ºC) on aroma in bread crumb were investigated. Fermentation with the highest yeast concentration (60 g/kg flour) resulted in bread containing the highest concentration of the majority of the compounds formed from yeast activity (e.g. 2,3-butanedione and phenylacetaldehyde), compared to doughs fermented at lower yeast concentrations (20 and 40 g/kg flour). A fermentation temIII perature at 5°C resulted in breads with the highest concentration of the three esters; ethyl acetate, ethyl hexanoate and ethyl octanoate, compared to breads fermented at higher temperatures (15 and 35°C). Fermentation at 15 and 35°C resulted in breads with the highest concentration of many lipid oxidation compounds (e.g. heptanal and hexanal) compared to breads fermented at 5°C.
In Paper III the effect of the type of commercial baker’s yeast (baker’s yeast I to VII, 2.88•1014 yeast CFU/kg flour) on bread aroma was investigated. Breads fermented by commercial baker’s yeast I to IV had the significantly highest concentration of 2,3-butanedione and 1-propanol compared to breads fermented by the other yeasts. Furthermore, 3-methylbutanal, 2-methyl-1-propanol and ethyl acetate were
found in significantly highest concentration in breads fermented by baker’s yeast I and II. Phenylacetaldehyde and 2-phenylethanol were found in the significantly highest concentration in breads fermented by baker’s yeast V and VI. The fact that dough fermentation time and bread aroma was significantly influenced by the type of commercial yeast indicates that some of the seven baker´s yeasts might differentiate in yeast strain.
Commercial baker’s yeast (level and type) and fermentation temperature are concluded to significantly influence the fermentation time and the aroma profile of bread crumb. Sensory analysis and analysis of acids and non-volatile compounds in breads fermented by the same conditions as in this PhD thesis could be relevant in future research studies.
| Originalsprog | Engelsk |
|---|
| Forlag | Department of Food Science, University of Copenhagen |
|---|---|
| Antal sider | 136 |
| Status | Udgivet - 2013 |