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Eur Food Res Technol (2005) 220:187–190
DOI 10.1007/s00217-004-0998-y
ORIGINAL PAPER
O. R. Afolabi · T. O. S. Popoola
The effects of baobab pulp powder on the micro flora involved
in tempe fermentation
Received: 26 September 2003 / Revised: 5 July 2004 / Published online: 8 September 2004
Springer-Verlag 2004
Abstract Locally prepared tempe that underwent natural
fermentation was characterized by the growth of Lacto-
bacillus plantarum,Streptococcus lactis,Bacillus sp.,
Salmonella sp., Klebsiella sp., Lactococcus lactis,Rhi-
zopus sp. and Staphylococcus sp., while fermentation
carried out with the addition of varying levels of baobab
pulp powder had mainly lactic acid bacteria (LAB)—
Lactobacillus plantarum,Lactobacillus fermentum,Lac-
tobacillus acidophilus and Rhizopus sp. dominating. In-
creasing concentrations of baobab pulp powder led to an
increase in the population of lactic acid bacteria (LAB)
from 2.310
2
to 3.310
4
while it reduced the population
of inoculated Rhizopus from 10
2
to only six colonies on
malt extract agar (MEA).
Keywords Fermentation · Tempe · Baobab
Introduction
Tempe is a nutritious fermented food obtained by the
fermentation of soybeans using the fungus Rhizopus oli-
gosporus. Although its consumption was initially con-
fined to the Asian countries, recently its consumption has
spread to other parts of the world, particularly developing
countries in Asia and Africa, including Nigeria, where it
plays an important role as a complementary food [1]. In
Nigeria, it is fast becoming popular as a dietary protein
supplement since animal protein is unaffordable by the
majority of the populace. The production of tempe varies
from one locality to another. In Indonesia and other parts
of Southeast Asia, tempe is prepared without the addition
of baobab pulp, but in Nigeria, where its consumption is
still limited, it is fermented with baobab pulp powder in
order to give the characteristic aroma and acidic taste
preferred by the local people. Baobab (Adansonia digi-
tata) pulp is rich in ascorbic acid, calcium, tartaric acid
and potassium bitartrate [2]. Its usage in food fermenta-
tion is a common practice in Nigeria, especially in the
northern part of the country where the Fulani Kraals use it
in the fermentation of cow milk for “nono” production.
The pulp is pounded gently into a powder by using a
pestle and mortar. It is then sieved to separate the seeds
from the powder. This is done to hasten the curdling
process as well as to improve the quality and quantity of
the product, especially during the dry season when cow
lactation is low and “nono” demand is high.
Production of tempe as it is done in Asia by fermen-
tation of soybeans with Rhizopus oligosporus brings about
changes in texture, aroma, and flavor, as well as reducing
anti-nutritional factors. It improves the nutritional quality
and produces an antibiotic effective against some gram-
positive bacteria including Staphylococcus aureus [3, 4].
Local communities in Nigeria are of the belief that the
addition of extracts of baobab to the fermentation medium
assist in achieving the improved sensory qualities desired.
Information on the process, microbiology and bio-
chemistry involved in tempe fermentation has been ex-
tensively reviewed [5, 6, 7, 8, 9]. Many pathogenic mi-
croorganisms such as Bacillus sp. [10, 11, 12], lactic acid
bacteria [13, 12] and yeasts [12] have been found in
tempe fermentation. The presence of these microorgan-
isms caused Tanaka et al. [14] and Nout et al. [16, 14]
to question the microbiological safety of tempe. They
demonstrated the ability of experimentally inoculated
species of Staphylococcus aureus,Clostridium botulinum,
Salmonella sp., Yersinia enterolitica and Bacillus cereus
to exhibit strong growth in the non-acidified beans during
fungal fermentation. These authors emphasized the im-
portance of acidification of the beans prior to fungal
fermentation for controlling the growth of these patho-
gens, if they are present. Apart from the slight acidity that
occurred during the fermentation of tempe, little infor-
mation is available on the possible ways of controlling the
undesirable microbes that grow during the soaking period.
Thus, the objective of this research is to determine the
O. R. Afolabi · T. O. S. Popoola ())
Department of Microbiology, College of Natural Sciences,
University of Agriculture,
P.M.B. 2240, 110001 Abeokuta, Nigeria
e-mail: topsiepop@yahoo.com
Tel.: +234-803-3280991
effect of the addition of baobab pulp on the pathogens that
develop in the fermentation medium during tempe pro-
duction.
Materials and methods
Collection of soybean samples
Soybean ( Glycine max. (L) Merr.) seeds used for the experiments
were obtained from the Department of Agronomy, Ladoke Akintola
University of Technology, Ogbomoso, Nigeria. The seeds were
sorted to remove extraneous materials and kept in a clean polythene
bag in the laboratory until used.
Preparation of tempe
Fifty grams of soybean seeds were weighed into six 1-l conical
flasks. The flasks were labeled A–F. Tempe was prepared from the
soybeans in each of the flasks according to the method of Robert et
al. [16]. The soybeans in each flask were boiled separately for
30 min, dehulled, and soaked in water. In each of the flasks (A–E),
5, 10, 15, 20 and 25 g of baobab pulp powder was added, respec-
tively. Baobab pulp powder was not added to flask F, however, as
this was to serve as the control experiment. Each flask was then
inoculated with 1 ml of Rhizopus oligosporus, obtained from the
University of Ibadan, Nigeria, to give 10
3
cfu/g. The flasks were
incubated overnight at room temperature (25 C) in a Mini/30/
CLAD/vis incubator.
Isolation procedure
The total viable counts of the microorganisms were determined on
plate count agar (PCA) (Oxoid) while lactic acid bacteria (LAB)
were isolated on MRS agar (pH 5.5) [17]. Yeasts and molds were
enumerated and isolated on malt extract agar (MEA) (Oxoid). The
Klebsiella sp. count was conducted on plates of MacConkey-Ino-
sitol-Potassium tellurite agar as described by Thomas et al. [18]. All
the plates were duplicated. Bacteria incubation was done using a
Mini/30/CLAD/vis incubator at 35 C, while fungi and mold were
incubated at 25 C in a separate incubator of the same model.
Determination of pH and titratable acidity
The pH of each tempe sample was determined using a combined
glass-calomel electrode and a pH meter (pHM61 Radiometer,
Copenhagen, Demark). Titratable acidity was done by titrating
25 ml of fermenting filtrate with 0.1 M NaOH. Three drops of 1%
phenolphthalein indicator were added. The titratable acidity present
in the sample was calculated based on the method of Nout et al.
[13]
Identification procedure
Systematic, morphological and biochemical tests were conducted
according to Cowan and Steel [19] with reference to Bergey’s
Manual of Systemic Bacteriology [20, 21]. Lactic acid bacteria
(LAB) were identified using the conventional method of Kandler
and Weiss [17] with complementary fermentation tests on API
50 CH gallery and CH medium (API system, Motalieu-Vercieu,
France).
Data analysis
The data generated from the pH and titratable acidity readings were
subjected to statistical analysis. The linear model procedure method
was used to find out which of the concentrations of baobab pulp
power has a maximum effect on the acidity of the medium during
tempe fermentation at p0.05.
Results and discussion
The dominant microorganisms isolated from the fermen-
tation medium apart from the Rhizopus oligosporus in-
oculum were mainly lactic acid bacteria (LAB). These
were identified as Lactobaccillus plantarum,Lactobacil-
lus fermentum,Lactobacillus acidophilus, and Lactococ-
cus lactis (Table 1). As the concentration of baobab pulp
powder increased, the acidic medium present in tempe
increased as well. This trend continued until the mold
(Rhizopus oligosporus) could no longer survive in the
medium. The mold was eliminated from the medium in
the flask containing 15 g of baobab powder. Hence, it
Table 1 Microorganisms isolated from tempe samples with baobab pulp
Sample Population (cfu/g) Microbial species
PCA MRS MEA MCIK
A 3.410
3
2.310
2
25 1.510
1
Streptococeus sp., Lactobaccillus plantarum,Klebsiella sp., Bacillus sp.
Staphylococcus sp., Rhizopus sp., Lactococcus lactis
B 2.910
2
2.310
3
15 - Streptococcus sp., Lactobacillus plantarum,Lactococcus lactis,Lactobacillus
plantarum ,Rhizopus sp.
C 2.010
2
2.810
3
10 - Lactococcus lactis,Lactobaccillus fermentum,Lactobacillus plantarum,
Lactobacillus acidophilus,Rhizopus sp.
D 7.910
1
3.110
3
6- Lactococcus lactis,Lactobacillus fermentum,Lactobacillus plantarum,
Lactobacillus acidophilus,Rhizopus sp.
E 6.810
1
3.310
4
-- Lactococcus lactis,Lactobacillus fermentum,Lactobacillus plantarum,
Lactobacillus acidophilus
F 4.910
5
1.210
1
30 1.210
3
Streptococcus sp., Bacillus sp., Staphylococcus sp., Lactococcus lactis,
Rhizopus sp., Salmonella sp., Lactobacillus plantarum
MCIK MacConkey-Inositol-potassium tellurite
MEA Malt extract agar
PCA Plate count agar
MRS De Man Rogosa Sharpe agar
188
could be assumed that the medium containing 15 g of
baobab pulp powder and 50 g of soybeans or a ratio of
3:10, baobab powder and soybean seeds could be ideal for
tempe production involving the addition of baobab pow-
der. A concentration of the pulp powder above this value
would prevent fungal fermentation, while the concentra-
tion below it may not control the growth of pathogenic
microbes that colonize the soybeans during the fermen-
tation.
Presently, the preparation of tempe involving the use
of baobab pulp powder is still a traditional art. There is no
form of quantification of the amount of pulp powder or
the soybean seeds. The quantity of the powder used usu-
ally depends on the arbitrary judgment of the consumers,
thus the pH of the final product varies.
The results of the investigation on the isolated mi-
crobes from soybeans in flask F (control) agree with the
work of Nout et al. [13]. These authors implicated L
plantarum (along with other microbes) as the dominant
lactic acid bacteria species in tempe fermentation. In
addition to this organism, other species of lactic acid
bacteria such as Lactobaccillus fermentum,Lactobaccil-
lus acidophilus , and Lactococcus lactic were also iso-
lated form baobab pulp fermented tempe in this study.
This could be due to the acidic environment created by
the baobab powder, which favors their rapid proliferation.
This is beneficial to consumers since most of the lactic
acid bacteria species are nontoxic and have been reported
to produce an enzyme that breaks the oligosaccharides in
soybeans down to their mono and disaccharide con-
stituents [22, 23]. The presence of lactic acid bacteria in
tempe prepared as it’s being done locally in Nigeria will
not only improve the digestibility of tempe, but will also
extend the shelf life of the product because of the pre-
servative attributes of lactic acid bacteria.
Although the possible source of the lactic acid bacteria
encountered in this study was not investigated, the in-
volvement of lactic acid bacteria in a diverse range of
fermentation processes have been reported [24]. The
possibility of baobab pulp powder as the source cannot be
completely ignored. Investigations into this aspect of the
study are on-going.
Titratable acidity (expressed as a percentage of lactic
acid) increased throughout the process of fermentation,
resulting in a gradual decline in pH. However, the pH of
tempe in the control flask indicated the presence of little
acid created by the natural fermentation process, hence,
the highest pH value of 4.6. The pH and titratable acidity
of samples D and E were significantly different from the
pH and titratable acidity of the control. Other treatments
were not significantly different at p0.05 (Table 2).
In conclusion, this study established that an acidic
medium, created by the addition of baobab pulp powder
to tempe fermentation could prevent the growth of
pathogenic bacteria such as Salmonella sp., Bacillus sp.,
and Streptococcus sp. Although this process is being done
in the local production of tempe in Nigeria, there seems to
be good scientific basis for this practice, particularly
when aspects of microbiological safety are considered.
References
1. Egunlety M (2002) Int J Food Sci Nutr 53:15
2. Okon PN (1973) Characterization and biochemical studies
of Adansonia digitata pulp used for ‘nono’ fermentation. MSc
Thesis (Biochemistry) Ahmadu Bello University, Zaria, Nigeria
3. Steinkraus KH, Hand DB, Van Bureu JP, Hackler LR (1960)
Pilot plant studies on tempe. In: Proceedings of Conference on
Soybeans Products for Protein in Human Foods, USDA, pp 75–
84
4. Liem ITH, Steinkraus KH, Crouk TC (1977) Production of
vitamin B-12 in tempe, a fermented soybean food. App 1.
Environ Microbiol 34:773–776
5. Wang HL, Hesseltine CW (1981) Use of microbial cultures:
legume and cereal products. Food Technol 35:79–83
6. Beuchat LR (1983) Indigenous fermented foods In: Reed G (ed)
Biotechnology, vol.5: food and feed production with microor-
ganisms. Verlag Chemie, Weinheim, pp 477–528
7. Beuchat LR (1984) Fermented soybean foods. Food Technol
38:64–70
8. Steinkraus KH (1983) Trend and current knowledge in tempe
research. Proceedings from the symposium on the utilization of
tempe for the improvement of health and nutrition, Jakarta,
Indonesia. pp 138–148
9. Hachmeister KA, Fung DYC (1993) Tempe: a mold modified
indigenous fermented food made from soybean and/or cereal
grain. Crit Rev Microbiol 19(3):137–188
10. Sudarmadji S, Markakis P (1978) Lipid and other changes
occurring during the fermentation and frying of tempe. Food
Chem 3:165–170
11. Nout MJR, Bonants-Van Laarhoven TMG, de Draux R, Gerats
IAGM (1985) The influence of source process variables and
storage conditions on the quality and shelf life of soybean
tempe. Antonie van Leeuwenhoek 51:532–534
12. Samson RA, Van Kooji JA, Beboer E (1987) Microbiological
quality of commercial tempe in the Netherlands. J Food Protect
50:92–94
13. Nout MJR, De Dren MA, Zuurbier AM, Bonants van Laar-
hoven TMG (1987) Ecology of controlled soybean acidification
for tempe manufacture. Food Microbiol 4:165–172
Table 2 pH and titratable acid-
ity of tempe sample Sample Concentration of Baobab pulp
powder (g) pH Titratable acidity expressed as
lactic acid %
A 5 3.8€1.4
a
0.30€0.02
a
B 10 3.5€0.80
a
0.33€0.07
a
C 15 3.3€0.30
a
0.35€0.15
a
D 20 2.8€1.2
b
0.40€0.20
b
E 25 2.35€1.1
b
0.43€0.18
b
F 0 (control) 4.6€0.80
a
0.28€0.12
a
Values represent the mean scores (n=3); Scores followed by the same letter in a column are not
significantly different (p0.5)
189
14. Tanaka N, Kovats SK, Guggisberg JA, Meske LM, Doyle MP
(1985) Evaluation of the microbiological safety of tempe made
from unacidified soybeans. J Food Protect 48:438–441
15. Nout MJR, Beernink G, Bonants-van Laarhoven TMG (1987a)
Growth of Bacillus cereus in soybean tempe. Int J Food
Microbiol 4:293–301
16. Robert KM, Graham HF, Ken AB (1989) The microbial ecol-
ogy of soybean soaking for tempe production. Int J Food
Microbiol 8:35–46
17. Kandler O, Weiss N (1986) Regular, non-sporing gram-positive
rods. In: Holt J (ed) Bergey’s manual of systematic bacteriol-
ogy, vol. 2. William and Wilkins, Baltimore
18. Thomas JM, Ciurana B, Jofre JT (1986) New, simple medium
for selective, differential recovery of Klebsiella sp. Appl
Environ Microbiol 51:1361–1363
19. Cowan ST, Steel JK (1970) The identification of medical
bacteria. Cambridge University Press, London
20. Krieg NR, Holt JG (1984) Bergey’s manual of systematic
bacteriology, vol. 1. Williams and Wilkins, Baltimore
21. Sneath PHA, Mair NS, Sharpe ME, Holt JG (1986) Bergey’s
manual of systematic bacteriology, vol 2. Williams and
Wilkins, Baltimore
22. Sanni AI, Ahrne S, Onilude AA (1995) Production of (- galac-
tosidase by Lactobacillus plantarum isolated from diverse
sources. J Basic Microbiol 35:427–432
23. Sanni AI, Onilude AA, Ogundoye OR (1997) Effect of bacteria
galactosidases treatment on the nutritional status of soybean
seeds and its milk derivative. Nahrung Foods 41:18–21
24. Sanni AI, Onilude AA, Ogunbanwo ST, Fadahunsi IF, Afolabi
RO (2002) Eur Food Res Technol 215:176–180
190