Journal of Sustainable Bioenergy Systems, 2012, 2, 33-36
http://dx.doi.org/10.4236/jsbs.2012.23005 Published Online September 2012 (http://www.SciRP.org/journal/jsbs)
Study on Temperature Gradients and Protein Enrichment
by Aspergillus oryzae in Solid-State Fermentation on
Packed Bed Bioreactor Using Jowar (Sorghum) Straw
as Substrate
Ganesh A. Bathe1*, Vilas S. Patil1, Ashish S. Chaurasia2*
1School of Chemical Technology, North Maharashtra University, Jalgaon, India
2Department of Chemical Engineering, Jaypee University of Engineering and Technology, Guna, India
Received July 18, 2012; revised August 20, 2012; accepted August 29, 2012
ABSTRACT
The packed bed solid state bioreactor designated as PBSSB is constructed in the present study. The experiments are
carried out in packed bed bioreactor with jowar straw and inoculated with Aspergillus oryzae. Temperature gradient has
been measured at different axial po sitions. It is found that the organisms grew rap idly during the p eriod from 20 to 30 h
during which heat generation is more. These results are in agreement with other researchers. The fermented jowar straw
shows threefold in crease in protein content. This can be utilized as high value nutritional feed to animals.
Keywords: Solid-State Fermentation; Packed-Bed Bioreactor; Aspergillus oryzae; Jowar Straw; Temperature Gradient
1. Introduction
India is an agrarian country. Around 60% - 65% of the
people directly or indirectly depend upon agriculture. The
Indian farmer community is facing very serious eco-
nomic crises due to unpredictable monsoon, low market
value for agro-product, etc. Pressure of economic crises
on agro-based industries can be reduced up to certain
level if scientific research will be concentrated more in
these areas. Solid state fermentation can be a potential
solution for upgrading the nutritive value of agricultural
products and has the possibility of having it carried out
on farms [1]. If solid state fermentation (SSF) can be
used efficiently for large capacity then we can serve in
better way for society. Overall efficiency of the solid
state fermentation (SSF) basically depends on three fac-
tors i.e. Energy, Economy and Environment.
Submerged fermentation (SmF) and solid state fer-
mentation (SSF) are the two bioconversion methods in
operation. Submerged fermentation (SmF) is well estab-
lished while the solid state fermentation (SSF) is still in
evolutionary state and under intensive research. Solid
state fermentation has been defined as the fermentation
on moist substrate and is carried out in the absence or
near ab sence of fre e water [2,3]. In this process, water is
present in the solid substrate whose capacity for liquid
retention varies with the type of biomass material.
The bioreactors for solid-state fermentation can be di-
vided into four types, based on type of aeration or the
mixed system employed [4]. These are tray column,
packed-bed column, rotating drum and fluidized bed
column. Heat accumulation is the serious problem in the
solid state fermentor an d is the major co ns ideration in the
design of large scale packed bed solid state bioreactor
(PBSSB). Several reasons are responsible for heat accu-
mulation in PBSSB includes low thermal conductivity
of biomass, absence of free water, channeling, etc. [5].
Channeling occurs when the fluid/gas flowing through
the packed bed and find a ‘preferred or fix path’ thr ough
the bed.
The current research work focuses on novel design of
PBSSB. Experiments are carried out to study the heat
accumulation at different heights of PBSSB and to ana-
lyze the C:N ratio and protein content of unfermented
and fermented samples. Aspergillus oryzae is chosen to
be the micro-organism growing on jowar straw.
2. Experimental Setup
The experimental setup of a packed bed solid state fer-
mentor is shown in Figure 1. It consists of a cylindrical
unit (1) with a capacity of 4.4 litres. It is 25 cm long ver-
tical cylinder with internal diameter of 15 cm. The mate-
rial used for the construction of fermentor system is
*Corresponding authors.
C
opyright © 2012 SciRes. JSBS

G. A. BATHE ET AL.
34
Figure 1. Packed-bed solid state bioreactor (PBSSB): (1)
Fermentation vessel; (2) Wire mesh with glass wool; (3)
PT100 thermocouple; (4) Data acquisition system.
thermocol. The base of fermentor is made up of wire
mesh (2) with air distributor to facilitate aeration. The
packed bed is aerated with a constant velocity of 0.2 m/s.
The bed temperatures are measured by thermocouple
PT100 (3) at different axial positions and recorded by a
data acquisition system (4).
3. Materials and Methods
3.1. Inoculum Preparation
Spores of Aspergillus oryzae (2 × 105 spores per ml) are
inoculated in Czapekdox broth having sucrose as carbon
source and incubated for 48 hours at 30˚C. After incuba-
tion 5% v/w inoculums is inoculated in the cooked sub-
strates.
3.2. Pretreatment of Raw Material
The known quantity of jowar straw is crushed in the
mixer and screened to a mean particle size of 0.25 cm -
0.27 cm for its utilization. The material is mixed with
water and cooked in an autoclave at 1 bar for 30 minutes.
The mixture is cooled to ambient temperature and then
dried in a convection oven so that the moisture is main-
tained up to 50% - 55%. In the present work constant
moisture is maintained and the effect of moisture content
on growth of microorganism is assumed to be negligible.
After drying, the mixture is inoculated with a spore sus-
pension at a rate of 2 × 105 spores/ml substrate dry matter
(SDM). The mixture is also sprayed with a mineral solu-
tion containing essential minerals like MgSO4, KH2PO4
and FeSO4. The mixture is then transferred in desired
quantities into PBSSB. The initial pH of the biomass is
measured with the method discussed by Chutmanop,
Chuichulcherm, Chisti and Srinophakun [6] as given in
Han and Anderson [7] and found to be 7.5.
4. Results and Discussion
The fermentation is carried out in PBSSB. The bioreactor
is aerated with a velocity of 0.2 m/s from the bottom of
the column. This air is purified us ing 0.2 micron air filter
before passing inside the column. The temperature at the
centre of the bioreactor with a total depth of 12 cm as a
function of time is shown in Figure 2. The temperature
increases within a fermentation period 10 - 30 h, except a
slight decrease in the span of about 10 - 15 h, probably
due to presence of lag phase. In the lag phase, there is no
heat evolution due to negligible growth of microorgan-
ism. The result indicates that the fermentation started at
around 10 h and maximum metabolic activity phase is
about 20 - 30 h. D uring the activ e grow th phase, th e tem-
perature increases from 34.5˚C to 37.4˚C due to high
oxygen requirement and heat generation.
The temperature plots at various bed depths during the
fermentation process are shown in Figure 3. The results
indicate that the temperatures at all the bed depths in-
crease gradually with the progress of fermentation proc-
ess from 10 - 35 h, and then decrease gradually. At the
bed depths of 2 cm and 6 cm, the maximum temperatures
reached are 36.1˚C and 36.4˚C respectively during the
fermentation period of 35 h. While at the bed depths of
12 cm, 16 cm and 21 cm, the maximum temperatures
reached are 37.4˚C, 37.6˚C and 37.8˚C respectively dur-
ing the fermentation period of 30 h, and then it is de-
clined in a linear fashion to reach 35.1˚C by about 15
Figure 2. Temperature profile along the depth of the fer-
mentor as function of time (Bed depth = 12 cm).

G. A. BATHE ET AL. 35
Figure 3. Temperature profiles at different bed depths of
the fermentor as function of time.
hours corresponding to the completion of the fermenta-
tion process. Thus, it is found that the temperature gra-
dient increase with the depth of the column. The results
indicate that the bed depth also affected the temperature
control in PBSSB. These results are in qualitative agree-
ment with Chen, Xu & Li [8], Fanaei & Vaziri [9], Cas-
taneda, Rojas, Bacquet, Raimbault & Gonzalez [10] and
Srinophakun & Srinophakun [11]. Chen, Xu & Li [8]
developed the bioreactor for solid-state fermentation
(SSF) and performed the temperature gradient studies
with different bed heights. Fanaei & Vaziri [9], Casta-
neda, Rojas, Bacquet, Raimbault & Gonzalez [10] and
Srinophakun & Srinophakun [11] developed the mathe-
matical model for packed-bed solid-state fermentation to
study the effects of various design and operating vari-
ables.
Tables 1 and 2 indicate the results of jowar straw
samples before and after fermentation respectively. The
samples are analyzed to find C:N ratio and protein con-
tent before and after fermentation. The C:N ratio above
16 is suitable for the growth of micro-organism in the
fermentation process [12]. Carbon source represents the
energetic source that will be available for the growth of
the micro-organism. As indicated in Table 1, the C:N
ratio of jowar straw sample is 18.45 and hence it is suit-
able biomass for fermentation process. The protein con-
tent in the biomass is analyzed by the standard method
used for the determination of protein in foods and feeds
(IS:7219:1973). It is found that the protein content of
fermented biomass is increased to 9.6 (% w/w) from the
initial value of 3.44 (% w/w) of unfermented biomass.
This protein rich biomass has high demand as the nutri-
tional animal feed. This result is in agreement with Han
and Anderson [7]. Han and Anderson [7] carried semi-
Table 1. Laboratory test results of jowar straw sample be-
fore fermentation.
Sr. No.Test
Parameters Measurement Unit Method Result
1 Organic
Carbon % w/w SW 8-Method 9060A 10.15
2 Nitrogen % w/w IS:7219:1973 0.55
3 C:N Ratio - By Calculation18.45
4 Protein % w/w IS:7219:1973 3.44
Table 2. Laboratory test results of jowar straw sample after
fermentation.
Sr. No.Test
Parameters Measurement Unit Method Result
1 Organic
Carbon % w/w SW 8-Method 9060A 5.44
2 Nitrogen % w/w IS:7219:1973 1.54
3 C:N Ratio - By Calculation3.53
4 Protein % w/w IS:7219:1973 9.6
solid fermentation on ryegrass straw and found fourfold
increase in the protein content.
5. Conclusion
The packed bed solid state bioreactor is constructed to
study the effects of heat accumulation and protein con-
tent in jowar straw. It is found that the temperature gra-
dient increase gradually with increase in bed depth. The
results indicate that the maximum metabolic activity
phase is 20 - 30 h during which heat generation is more.
The fermented sample is analyzed for protein content. It
is found that protein content of jowar straw increases
from 3.44 (% w/w) to 9.6 (% w/w). This indicates the
applicability of PBSSB for protein enrichment of bio-
mass and its direct applicability for animal feed. PBSSB
developed in the presen t study is su itable f or clo sed static
fermentation to get value added biomass. It can be fur-
ther modified to other biomass materials and microor-
ganisms systems where product has high added value.
6. Acknowledgements
The author would like to thank to the University Grants
Commission (UGC), India for financially supporting the
minor research project in physical sciences, biosciences,
maths, medical, agriculture sciences and engineering &
chemistry to university/college teacher. This project is
supported by UGC under the project entitled “Tempera-
ture gradient studies in packed bed solid state fermen-
tor—F. No. 39-1013/2010 (SR)”.

G. A. BATHE ET AL.
36
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