A sufficiently high degree of accumulation of lactic acid is achieved at this
duration. The subsequent increase in duration leads to a significant deceleration of the
fermentation process, which is not efficient.
Chemical composition and antimicrobial activity of fermented birch sap.
The chemical composition of fermented birch sap, as evidenced by the results of the
research conducted, does not have significant differences from the freshly-collected
birch sap in terms of the total content of dry matter and mineral substances, but
significantly differs in the level of total acidity. Its concentration rises to 0.5-0.6%
resulting from the application of the starter culture of Lactobacillus casei ssp. аlactosus
(fermentation by the homofermentative type) and due to the presence of lactic acid in
it.
Using high-performance liquid chromatography (HPLC), we found that mainly
two acids are accumulated in the fermented birch sap namely lactic and succinic
(Figure 8). Succinic acid is produced by cells when the accumulation of a large amount
of lactic acid disturbs lactic-acid bacteria's own metabolism, and they become unable
to include the obtained succinic acid in the subsequent reactions of citric acid cycle.
Birch sap is poor in organic acids, and its main acid is malic one. It was logical
to lay account with its presence in the fermented juice as well. So we also applied malic
acid to the standard mixture while determination of the oxy acids. On the
chromatogram malic acid's peak is located between citric and succinic ones (Figure 8).
Figure 8. Chromatogram of oxy acids of fermented birch sap
As is evident from Figure 8, fermented birch sap showed no signs of neither malic
nor ascorbic acid. Most likely they were used by lactobacilli in the process of their life
cycle. There were detected lactic and succinic acids, and also an unidentified peak with
Rf 3.64. Two other acids with Rf 1.87 and Rf 2.01 were detected, but were not
identified. Perhaps they are remnants of acids (acetic and boletic) that due to the juice
pasteurization are not used by lactobacilli in the course of lactic acid's creation. Thus,
total titrated acidity of the fermented birch sap is formed mainly by two organic acids:
lactic and succinic.
Figure 9 displays a chromatogram of phenol acids in a fermented birch-apple
blend. As it is seen, there were chlorogenic (Rf 10,63) and caffeic (Rf 10.97) acids,
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