EFECTO DEL pH INICIAL DE DESARROLLO DE Pleurotus ...

ABSTRACT
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The effect of initial pH of development of Pleurotus ostreatus on the laccases activity
was evaluated. A liquid medium previously used to produce laccases containing glucose
as carbon source, yeast extract as nitrogen source, copper sulfate as inducer of
laccases and other minerals at four different pH values (3.5, 4.5, 6.5 and 8.5) was
tested. Were reported the kinetic parameters of development of the fungus (µ, X max ,
Y X/S , q s ) and the laccases production (Productividad, Y E/X , q p y E max ) for all submerged
fermentations. The laccases activity was determined using 2.6-dimethoxyphenol as
substrate.
High values of µ were obtained at pH 3.5 without yeast extract and pH 4.5 (0.037 and
0.034 h -1 respectively). On the other hand, high X max values were observed at pH 6.5
and 8.5 (6.7 g/L and 8.3 g/L respectively). The maximal laccases activity value was
observed in the fermentation developed at pH 6.5 (36500 U/L) at 432 h and evaluated at
the same pH. However, in fermentations at initial pH 4.5 and 8.5 were obtained values of
laccases activity of 33500 U/L and 21000 U/L, respectively. The lower laccases activity
values were observed in the fermentation at pH 3.5 with and without yeast extract (4030
U/L and 462 U/L, respectively). The zymograms were revealed at different pH values
(3.5, 4.5, 6.5 and 8.5), were observed up to 6 different isoforms during fermentation at
pH 8.5 revealed at pH 4.5; on the other hand, 3 isoforms were observed in the
fermentation at pH 6.5 revealed a pH 4.5 and two different isoforms in the other
fermentations in all pH values of activity evaluated.
It was observed that the pH of development of the fungus is a factor that modifies the
pattern of production of laccases, as well as some enzymes has not the same optimal
pH for production and activity. Different laccases activities and number of isoforms were
dependent of pH of development of the fungus.