Mixed Culture Fermentation In The Hydrolysis Of Cereal Flour For The Production Of Industrial Biochemicals

ABSTRACT

Hydrolysis of a complex medium (whole-wheat flour) using a mixed culture of

Aspergillus. awamori and Aspergillus. oryzae was carried out for the purpose of

producing a fermentation medium that can be used to produce industrial chemicals..

The experimentation was carried out in shake flasks as well as in a 10-litre fermenter and

the results obtained in all cases indicated that the two microorganisms could cooperate

together to hydrolyse both the starch and the protein in wheat flour concurrently. The

mixed culture hydrolysis produced a medium with an optimum total reducing sugar of

about 50 g/l and free amino nitrogen concentration of about 120 mg/l.

The amount of reducing sugar obtained for the pure cultures of the two organisms when

compared with that of the mixture showed that A. awamori gave a slightly higher rate of

fermentation. A. awamori produced 50 g/l of reducing sugar in 30 h when compared with

A. oryzae and the mixed culture producing the same amount in 42 h and 39 h

respectively. The glucoamylase activity of the mixture was higher in the mixed culture

than in either of the pure cultures.

The highest yield of free amino acid (120 mg/l) was obtained in the fermentation with A.

oryzae and the least value of (56 mg/l) was with that of A. awamori. The mixed culture

gave a value of (115 mg/l) which is comparable to that obtained with A. oryzae. The

protease activity followed the same trend as was observed for the production of free

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amino acid with the highest activity being observed with A. oryzae and the least with A.

awamori.

A mathematical model was developed for the hydrolysis of starch, based on proposed

mechanism assuming a synergistic relationship in the action of the amylases (amylase

and glucoamylase) produced by the two organisms. The model incorporates the syntheses

of the two enzymes by the organisms and assumes a Michaelis-Menten model without

substrate or product inhibition for the hydrolysis. Futhermore the mechanism assumes a

homogeneous structure of the substrate predicts only one final product and lacks

information on all possible intermediate products.

The solution of the multiparameter model as it is usual with this type of model did not

permit a wide variation of most of the parameters. Some parameters such as the ratio of

Michaelis-Menten equilibrium constant and the turnover number for the two enzymes

1

1

m

cat

k

k

 

 

 

and 2

2

m

cat

k

k

 

 

 

represented by 1 K and 2 K could be varied between 10-110 and

1000-3800 respectively. Others like specific growth rates (  ), enzyme constant (a) and

the number of cleavable bonds in the oligosaccharides per molecule of substrate (n) had a

narrow range of values. The value of (  ) was between 0.04-0.25 h-1 and (n) had a value

of 2 and the enzyme constant (a) had a value of 1-5. .

The experimental data were very well predicted by the developed model.

The model can therefore be used to predict the extent of hydrolysis of complex media by

a mixed culture of A. awamori and A. oryzae.