Table 1 Accumulation of lactic-acid bacteria's biomass
depending on the dose of seed material
Strain
number
Quantity of
starter culture.
%
Number of lactobacilli (CFU/cm3) over the fermentation period (full days)
1
2
3
4
5
6
0.2
0.6 х 102
1.9 х 104
6.1 х 105
0.4 х 107
3.4 х 107
0.3
3.7 х 103
6.2 х 104
8.1 х 105
0.9 х 108
1.3 х 108
0.5
0.4 х 104
4.7 х 104
9.0 х 106
1.1 х 108*
1.2 х 108
0.7
8.1 х 104
0.2 х 107
1.2 х 108*
1.3 х 108*
1.1 х 108
12
0.2
0.7 х 103
2.1 х 103
6.6 х 105
4.1 х 106*
3.6 х 107
0.3
3.9 х 103
6.3 х 104
2.9 х 106
1.1 х 108*
1.2 х 108
0.5
4.1 х 103
5.1 х 105
9.3 х 106
1.3 х 108*
1.3 х 108
0.7
8.4 х 104
0.7 х 107
1.3 х 108*
1.4 х 108*
1.2 х 108
Note: * – this mark in the table highlights the values of CFU, corresponding to
the beginning of steady state of lactobacilli growth.
Thus, to obtain lactic-acid bacteria-fermented birch sap, it is enough to pasteurize
the birch sap at (80 ± 2)°C for (10 ± 1) minutes, apply about 3% of the seed material
and store it at room temperature close to (20 ± 2)°C in a hermetically sealed containers
to protect them against aerobic microorganisms' ingestion – from film yeast and mold.
Upon achievement of a total juice acidity of 0.3-0.6%, it can be transferred for
processing within three months.
Dependence of lactobacilli activity on sugar concentration in the substrate.
The activity of lactobacilli was determined by measuring the losses of dry soluble
substances in the juice during the fermentation process and accumulation of titrated
acids on lactic basis.
The content of sugars in birch sap is relatively low. Its fluctuations, depending on
the weather conditions and place of cultivation, can range from 0.5 to 0.9%. As it was
already mentioned, the final product of sugars' fermentation by lactobacilli is mainly
lactic-acid and other substances (acetic acid, ethyl alcohol, carbon dioxide, dextrin, and
mannitol) in small quantities [4].
As the fluctuations of sugar content in fresh juice are quite significant, it was
necessary to determine the activity of its loss in the process of fermentation. The
dynamics of lactic-acid accumulation (according to the content of titrated acidity),
depending on the concentration of sugar added to the substrate within a period of five
full days, is presented in Table 2, and dynamics on the second and fifth days at Figure
1.
Consequently, birch sap fermentation time to the desired lactic-acid content can
be adjusted by adding a certain amount of sugar into it. According to the derived
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