Guzel-Seydim et al.120 followed the production of organic acids and volatiles
during the fermentation of kefir produced in the laboratory from grains obtained
from Turkey. Lactate production started slowly but the concentration of lactate rapidly
climbed to 6000 μg/g by the end of the 22 h fermentation. Citrate, the next most
abundant organic acid, declined during fermentation from 1760 to 1440 μg/g at the
end of the fermentation. Pyruvate levels increased during fermentation to a final
level of 18 μg/g. Levels of orotate and urate declined over the 22 h period; hippurate
was totally consumed after 15 h. Acetic acid, propionic acid, and butyric acid were
not found in any samples. Diacetyl was also absent. Acetaldehyde and acetoin levels
increased as the fermentation progressed. However, ethanol production did not begin
until after 5 h in the fermentation. Guzel-Seydim et al.121 also studied the changes
in organic acids and volatile flavor compounds in kefir stored at 4°C for up to 21 d.
Lactate was the organic acid in highest concentration (> 6000 μg/g), followed bycitrate (1500 μg/g). Lactate increased slightly during storage. Pyruvate was found at
day zero, but by day seven of storage it had disappeared. The conversion of pyruvate
to ethanol and CO2 may account for this observation. This stored kefir contained
no hippuric acid, acetic acid, propionic acid, or butyric acid. Acetaldehyde levels
doubled (to 11 μg/g) during storage, whereas acetoin levels decreased from 25 to 16
μg/g during the storage period. This group found no diacetyl in their kefir.
Guzel-Seydim et al.120 followed the production of organic acids and volatilesduring the fermentation of kefir produced in the laboratory from grains obtainedfrom Turkey. Lactate production started slowly but the concentration of lactate rapidlyclimbed to 6000 μg/g by the end of the 22 h fermentation. Citrate, the next mostabundant organic acid, declined during fermentation from 1760 to 1440 μg/g at theend of the fermentation. Pyruvate levels increased during fermentation to a finallevel of 18 μg/g. Levels of orotate and urate declined over the 22 h period; hippuratewas totally consumed after 15 h. Acetic acid, propionic acid, and butyric acid werenot found in any samples. Diacetyl was also absent. Acetaldehyde and acetoin levelsincreased as the fermentation progressed. However, ethanol production did not beginuntil after 5 h in the fermentation. Guzel-Seydim et al.121 also studied the changesin organic acids and volatile flavor compounds in kefir stored at 4°C for up to 21 d.Lactate was the organic acid in highest concentration (> 6000 μg/g), followed bycitrate (1500 μg/g). Lactate increased slightly during storage. Pyruvate was found atday zero, but by day seven of storage it had disappeared. The conversion of pyruvateto ethanol and CO2 may account for this observation. This stored kefir containedno hippuric acid, acetic acid, propionic acid, or butyric acid. Acetaldehyde levelsdoubled (to 11 μg/g) during storage, whereas acetoin levels decreased from 25 to 16μg/g during the storage period. This group found no diacetyl in their kefir.
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