3. Results
3.1. Influence of nutrients on yeast growth
We compared the effect of yeast nutrients (yeast extract and
DAP) and different banana concentrations (2, 4, and 6%) on the
growth of commercial wine yeast during fermentation. Each batch
was inoculated with 1% volume of a yeast culture in YMbroth, with
a final cell count of 2 107 cfu/ml. Fig. 1 shows the growth kinetics
of viable yeast cells at different yeast nutrients during alcoholic
fermentation. Blueberry musts contained about 104~106 cfu/ml on
the first day of fermentation and the concentration remained
steady for about 10 days. After that time, the number of viable yeast
cells in the musts began to decrease, and the populations reached
little more than 104 cfu/ml in all tested samples after 22 days of
fermentation. Although similar, the population growth pattern
displayed by yeast growth in blueberry must without yeast nutrients
(control) showed several variations from the tested samples.
The number of viable cells gradually decreased starting from the
first day of fermentation, and the population stabilized at approximately
5 103 cfu/ml after 22 days of fermentation, indicating that
the early addition of yeast nutrients (DAP and yeast extract) and
banana affected the evolution of yeast during fermentation. In all
cases, the yeast viability was greater than the control starting from
the 12th day of fermentation. Nevertheless, the specific growth rate
did not vary according to different yeast nutrients added prior to
fermentation.