Abstract
In paper I and II, the influence of different fermentation temperature (8°C, 16°C and 32°C) and
yeast level (2%, 4% and 6%) on the formation of volatile compounds in wholemeal wheat bread
were investigated. The fermentation times were regulated to optimum bread height for each
treatment. The volatile compounds were extracted with dynamic headspace extraction and
analyzed with gas chromatography-mass spectrometry. The results were evaluated using
multivariate data analysis and ANOVA.
In paper I, the crumb fermented at high temperature (32°C) had higher relative areas of the
Maillard reaction products 2-furancarboxaldehyde, 2-acetylfuran, 2-methylpyrazine and
phenylacetaldehyde. At low temperature (8°C and 16°C) the crumb was characterized by
having higher relative areas of the fermentation products 3-methylbutanal, 2-methylbutanal,
ethyl acetate, ethyl hexanoate, ethyl propanoate and 3-methylbutanol. Fermentation with low
yeast level (2%) resulted in bread with higher relative areas of 2- and 3-methylbutanal as well
as (E)-2-nonenal and (E,E)-2,4-decadienal as important lipid oxidation compound in bread.
Contrary, fermentation of bread with 6% yeast resulted in higher relative area of the important
fermentation product 2-phenylethanol. High yeast concentration (6%) was able to reduce the
relative areas of important lipid oxidation products.
In paper II, 28 volatile compounds out of 58 compounds were identified and the other 30
compounds were tentatively identified in the crust. Higher fermentation temperatures promoted
the formation of Maillard reaction products 3-methyl-1-butanol, pyrazine, 2-ethylpyrazine, 2-
ethyl-3-methylpyrazine, 2-vinylpyrazine, 3-hydroxy-2-butanone, methional and 5-methyl-2-
furancarboxaldehyde whereas at lower temperature (8°C) the formation of 2- and 3-
methylbutanal was favoured. Higher levels of yeast promoted the formation of 3-methyl-1-
butanol, 2-methyl-1-propanol and 3-(methylsulfanyl)-propanal, whereas hexanal was promoted
in the crust fermented with lower yeast level.
In paper III the degradation of inositol hexaphosphate (IP6) was evaluated in wholemeal wheat
dough fermented with different strains of S. cerevisiae (L1.12 or L6.06) or P. kudriavzevii
(L3.04) with extracellular phytase activity, in order to see if the degradation of IP6 in wholemeal
dough could be increased by fermentation with phytase-active yeasts. Samples were taken at
different stage of bread-making; after mixing, after fermentation and after baking. Around 60 to
70% of the initial value of IP6 in the flour (1002 mg/g) was reduced after dough mixing and
additional 10 to 20% after fermentation. No further degradation of IP6 was observed in all bread
after baking. Dough added with baker's yeast had the highest IP6 degradation after mixing and
dough fermented with P. kudriavzevii L3.04 or S.cerevisiae L1.12 had the highest degradation
with the same content of IP6 (100 mg/100g) after fermentation. Although S.cerevisiae L6.06 had
the highest extracellular volumetric phytase activity (28.8 ± 0.002 mU/mL), the IP6 content after
fermentation was in the same level of baker´s yeast (207 mg/100g) suggesting that the phytase
activity from this yeast strain might be suppressed by reaction products in the dough. Longer
mixing time resulted in longer reaction time for the wheat phytase, so the activity of wheat
phytase in dough seems to be the primary source of phytate degradation. Additional
degradation can be achieved by fermentation with phytase active yeast dependent on yeast
strain.
In this experimental work, fermenting wholemeal wheat dough at high temperature (32°C) with
high yeast level (6%) might produce bread with high level of important volatile compounds in the
crumb and crust which are mostly generated from fermentation process and Maillard reaction
respectively, and this bread might have the highest degradation of IP6 contributed by the
activities of wheat phytase and yeast phytase compared to other fermentation conditions use in
this study. S.cerevisiae L.1.12 might be more efficient in reducing the amount of IP6 in dough
with short fermentation time which is suitable for the baking industry.
yeast level (2%, 4% and 6%) on the formation of volatile compounds in wholemeal wheat bread
were investigated. The fermentation times were regulated to optimum bread height for each
treatment. The volatile compounds were extracted with dynamic headspace extraction and
analyzed with gas chromatography-mass spectrometry. The results were evaluated using
multivariate data analysis and ANOVA.
In paper I, the crumb fermented at high temperature (32°C) had higher relative areas of the
Maillard reaction products 2-furancarboxaldehyde, 2-acetylfuran, 2-methylpyrazine and
phenylacetaldehyde. At low temperature (8°C and 16°C) the crumb was characterized by
having higher relative areas of the fermentation products 3-methylbutanal, 2-methylbutanal,
ethyl acetate, ethyl hexanoate, ethyl propanoate and 3-methylbutanol. Fermentation with low
yeast level (2%) resulted in bread with higher relative areas of 2- and 3-methylbutanal as well
as (E)-2-nonenal and (E,E)-2,4-decadienal as important lipid oxidation compound in bread.
Contrary, fermentation of bread with 6% yeast resulted in higher relative area of the important
fermentation product 2-phenylethanol. High yeast concentration (6%) was able to reduce the
relative areas of important lipid oxidation products.
In paper II, 28 volatile compounds out of 58 compounds were identified and the other 30
compounds were tentatively identified in the crust. Higher fermentation temperatures promoted
the formation of Maillard reaction products 3-methyl-1-butanol, pyrazine, 2-ethylpyrazine, 2-
ethyl-3-methylpyrazine, 2-vinylpyrazine, 3-hydroxy-2-butanone, methional and 5-methyl-2-
furancarboxaldehyde whereas at lower temperature (8°C) the formation of 2- and 3-
methylbutanal was favoured. Higher levels of yeast promoted the formation of 3-methyl-1-
butanol, 2-methyl-1-propanol and 3-(methylsulfanyl)-propanal, whereas hexanal was promoted
in the crust fermented with lower yeast level.
In paper III the degradation of inositol hexaphosphate (IP6) was evaluated in wholemeal wheat
dough fermented with different strains of S. cerevisiae (L1.12 or L6.06) or P. kudriavzevii
(L3.04) with extracellular phytase activity, in order to see if the degradation of IP6 in wholemeal
dough could be increased by fermentation with phytase-active yeasts. Samples were taken at
different stage of bread-making; after mixing, after fermentation and after baking. Around 60 to
70% of the initial value of IP6 in the flour (1002 mg/g) was reduced after dough mixing and
additional 10 to 20% after fermentation. No further degradation of IP6 was observed in all bread
after baking. Dough added with baker's yeast had the highest IP6 degradation after mixing and
dough fermented with P. kudriavzevii L3.04 or S.cerevisiae L1.12 had the highest degradation
with the same content of IP6 (100 mg/100g) after fermentation. Although S.cerevisiae L6.06 had
the highest extracellular volumetric phytase activity (28.8 ± 0.002 mU/mL), the IP6 content after
fermentation was in the same level of baker´s yeast (207 mg/100g) suggesting that the phytase
activity from this yeast strain might be suppressed by reaction products in the dough. Longer
mixing time resulted in longer reaction time for the wheat phytase, so the activity of wheat
phytase in dough seems to be the primary source of phytate degradation. Additional
degradation can be achieved by fermentation with phytase active yeast dependent on yeast
strain.
In this experimental work, fermenting wholemeal wheat dough at high temperature (32°C) with
high yeast level (6%) might produce bread with high level of important volatile compounds in the
crumb and crust which are mostly generated from fermentation process and Maillard reaction
respectively, and this bread might have the highest degradation of IP6 contributed by the
activities of wheat phytase and yeast phytase compared to other fermentation conditions use in
this study. S.cerevisiae L.1.12 might be more efficient in reducing the amount of IP6 in dough
with short fermentation time which is suitable for the baking industry.
| Original language | English |
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| Publisher | Department of Food Science, Faculty of Science, University of Copenhagen |
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| Number of pages | 139 |
| Publication status | Published - 2016 |