Materials and methods
2.1 Preparation of fungal spore inoculum
Spore suspensions of Aspergillus oryzae
TISTR 3102 were prepared from a fully sporulated
(7 days old) PDA slant culture using 10 ml of 0.85%
NaCl solution. This spore suspension was used as the
master suspension, which was appropriately diluted to
required density. Spore concentration in the inoculum
was estimated by a haemacytometer.
2.2 Substrate preparation
Two economic crops consisting of rice (Oryza
sativa L.) and cassava (Manihot esculenta) were used
in the experiment. The 400 g (on a dry basis) of each
substrate was weighed separately into a 2-l Erlenmeyer
flasks and distilled water containing 10% (v/v) of
supplementing salt solution (30 ppm of CaCl2) was added
and adjusted to 60% moisture level (8). The contents
of the flasks were mixed thoroughly and autoclaved at
121°C for 15 minutes.
2.3 Solid-state fermentation
The sterilised solid substrate was inoculated
with one ml of the prepared inoculum. The contents
were mixed thoroughly and incubated at 30°C for 7
days. Samples of triplicate flasks were withdrawn after
desired incubation.
2.4 Mashing
The fermented mass was mixed into water to
form the slurry of 30% w/v (on a dry basis). One litre of
the slurry was added with 0.03 g of CaCl2 and adjusted
to pH 6 by using 0.1 M lactic acid. Mashing was carried
out by following the method of Okafor and Iwouno (9).
The slurry was initially mashed at 50°C and allowed
to stand for 30 min. The supernatant was decanted and
the remained flour was heated until it gelatinized at
88°C. The supernatant was returned to the cooled and
elatinized slurry, giving an overall temperature of 62°C.
The mash was held at this temperature for 60 min.
The pH of the mash was tested and adjusted to 5.6 by
adding a few drops of lactic acid. One-half of the mash
was withdrawn, boiled and returned to the main mash
and the temperature increased to between 69 and 71°C.
The mixture was held at this temperature for 60 min. The
mash was cooled and filtered using funnel and folded
Whatman No. 1 filter paper. The filtered solution was
finally boiled for 60 min to yield the malt rice syrup.
2.5 Measure of total reducing sugar (TRS)
and free amino nitrogen (FAN)
The samples of fermented mass were diluted
with distilled water and analysed for TRS and FAN
following the methods of Miller (10) and Lie (11)
respectively.
2.6 Enzyme activity
Crude enzyme from the fermented mass was
extracted by simple extraction. A fermented mass of 10 g
was mixed thoroughly with distilled water to a total
extract volume of 100 ml. Contents were mixed by
shaking for one hour at 30°C on a 150 rpm shaker. At
the end of the extraction, the suspension was centrifuged
at 7,000 rpm for 10 min. The extracted solution was
measured for amylolytic activity, α-amylase activity
and α-glucosidase activity.
2.7 Determination of amylolytic enzyme
and α-amylase
The amylolytic activity was assayed using the
Terashima method (12) after crude extraction of malted
rice. 0.5 ml of the supernatant was added to 0.5 ml of a