Abstract:
In Algeria, significant amounts of date rejects are generated with each harvest. These date rejects, rich
in fermentable sugars, rock salt and vitamins can be a medium favorable as well for the development
of the micro-organisms as for the production of the metabolites to strong added value such as the
amylolytic enzymes, in particular l'α-amylase.
With an aim of selecting new producing moulds d'α-amylase and of optimizing a culture medium
containing date rejects, five moulds of which Rhizopus sp1., Rhizopus sp2. Penicillium sp1.,
Alternaria sp. and Helminthosporium sp. were isolated starting from the grains from barley and were
cultivated on date must for the production of this enzyme by submerged fermentation. The kinetics of
production of biomass and α-amylase was studied while being based on the daily calculation of the
biomass and the proportioning of the enzymatic activity by the method of Bernfeld.
In order to improve considerably the development of these moulds and the d'α-amylase production, the
basic medium was enriched by various sources carbon, nitrogen and by phosphorus, and was
optimized by using a statistical method of experimental planning (matrices of Plackett-Burmun).
Our results showed that the biomass appears as of the first hours of incubation and reached its
maximum at 72 hours for the strains of Rhizopus sp. (1 and 2), Alternaria sp. and Helminthosporium
sp. and to 96 H for the strains of Penicillium sp., whereas the secretion of the enzyme begins only at
48 hours to reach its maximum at 72 hours for the strains of Rhizopus sp. (1 and 2) and at 96 hours for
the stocks Penicillium sp., Alternaria sp. and Helminthosporium sp.
The statistical analysis allowed the selection of the yeast extract, the starch, the KH2PO4, urea and the
temperature like factors positively influencing the production of biomass by all the strains, and the
yeast extract like the most influential factor positively on the α-amylase production by the five strains,
compared to the factors: pH, temperature, starch, urea and KH2PO4 whose influence varies from one
strain to another.
