Effect of culture pH on the growth characteristics and
exopolysaccharide production by Lactobacillus delbrueckii subsp. bulgaricus
Ropy strain
(Pengaruh pH
kultur terhadap sifat pertumbuhan dan produksi eksopolisakarida oleh Lactobacillus
bulgaricus subsp. bulgaricus strain ropy)
ABSTRACT
The effect of
environmental condition on EPS production by Lactobacillus bulgaricus was
studied using initial pH from 4.5 to 8.5 in SMR 10% at 30oC for 16 h
of incubation time. The initial pH influence
the EPS production, that the optimal pH condition was 6.5 – 8.5.
Key Words :
Exopolysaccharides, Lactobacillus bulgaricus, initial pH.
ABSTRAK
Pengaruh
kondisi lingkungan terhadap produksi EPS oleh L. bulgaricus dipelajari dengan menggunakan pH media awal mulai
dari pH 4,5 sampai 8,5 pada SMR 10% dengan menggunakan suhu inkubasi 30oC
selama 16 jam. PH awal media
mempengaruhi produksi EPS dimana pH optimal untuk produksi EPS adalah pH 6,5
sampai 8.5.
Kata Kunci :
Eksopolisakarida, L. bulgaricus,
pH awal
INTRODUCTION
Lacrobacillus delbrueckii
subsp. bulgaricus are used in the dairy industry to transform milk into
yoghurt (Chervaux et al., 2000).
Several strains which are capable of forming exopolysaccharide (EPS)
have been isolated and analyzed (Grobben et al., 1998).
The EPS production by lactic acid
bacteria is an important characteristic to be considered when selecting starter
culture for fermented milks. This type
of polymers prevents the wheing-off and improves the texture of the final product. However, there is no single set of culture
conditions that guarantees high EPS yields in all producing microorganism since
cells differ in their carbon source utilization, mineral requirements and even
temperature for an optimal EPS synthesis.
Mozzi et al., (1994) have
been reported that pH of medium is a critical factor for the EPS production by Lactobacillus
casei.
The effect of environmental
conditions on the EPS formation by lactic acid bacteria was mainly studied in
thermophilic species of technological interest (Malaka, 1997). In resent years, mesophilic lactic acid
bacteria like Lactobacillus delbrueckii became important microorganisms
as producer of EPS. However little
attention has been paid to the ability of these lactic acid bacteria to produce
EPS under different pH culture.
According the above considerations,
the aim of this study was to determine the influence of the initial pH on the
EPS production by Lactobacillus delbrueckii subsp bulgaricus ropy
strain when growing in milk.
MATERIALS AND METHODS
Microorganism
L. delbrueckii subsp. bulgaricus ropy strain was obtained
from the culture collection of Research Center of Hasanuddin University. Stock cultures were kept in 10% sterile
reconstitution skim milk (RSM) at –20oC.
Growth conditions
10% RSM (sterilized at 121oC
for 15 min) were used as growth media.
The pH was adjusted after sterilization with lactic acid to initial
values of 4.5, 5.5, 6.5, 7.5 and 8.5.
Fermentations were performed at 30oC
(according to our experiment before for temperature optimal to EPS production)
in Erlenmeyer containing 100 ml of growth media inoculated with a 16 h active
culture at the rate of 1% (v/v) (about 108 cfu/ml) inoculums. Samples were taken at 16 h, and cooled before
the assays. Cell viability was
determined by the agar plate method using BCP agar. Serial dilutions of each sample were plated
in duplicate and plates were incubated at 37oC for 48 h. Results were expressed as colony forming
units (cfu/ml).
Exopolysaccharide isolation
The EPS obtained from
the cell free supernatants and isolated according Mozzi et al. methods
(1994). The EPS production was expressed
as mg/l. EPS was freeze-dried and stored
at 4oC. The EPS production
was expresses as mg/l (Mozzi et al., 1994).
Titratable acidity and pH
Titratable acidity, expressed as
lactic acid percentage, was measured according to Mozzi et al.
(1994). PH was measured using pH-meter
(Hanna-pH meter).
Experimental Design
The effect of pH of media on
activity and EPS production of L. bulgaricus was studied using RSM
10%. Initial pH values were 4.5, 5.5,
6.5, 7.5, and 8.5. pH value of 4.5 and
5.5 represented as acid conditions, 6.5 represented as pH of milk and 7.5 and
8.5 represented as base condition. After
incubation for 16 h, the amount of nutrient consumed as well as the colony
counts, lactic acid produced and the EPS formed increased when increasing the
initial pH from 4.5 to 6.5 and constant at pH 7.5 (Fig. 1 – 3).
Fig. 1. Exopolysaccharide
production by L. bulgaricus in
different initial pH medium.
The EPS production in skim milk
reconstitution 10% after 16 of incubation time was increased from 128.6 mg/l to
326.2 mg/l (with pH 4.5 to 6.5). When
comparing the behaviour of L. bulgaricus
in SMR 10% on pH change (0 h and 16 h of incubation time), was valuable
change. In 4.5 of initial pH cause of
increased the pH medium to 4.8. This
effect maybe cause of L. bulgaricus
would exist in it subcritis environment.
However, with increase the initial pH, L. bulgaricus more activated to produce of lactic acid so the pH of
medium decrease (Fig 2).
Fig. 2. The pH change in
intial pH (0 h of incubation time) and
final pH (16 of incubation time) by L.
bulgaricus in SMR 10%.
The growth of L. bulgaricus in SMR 10% medium was related
to the metabolism of glucose to lactate in the pH range assayed, while in the
latter one a partial uncoupling between growth and lactate formation was
observed. This could be attributed to
the effect of the initial pH and certain nutrient limitation on the cell
growth, which would reduce the viability of the cells with low effect on the
rate of carbohydrate metabolism.
Fig. 3. Production of lactic acid in SMR 10% by L. bulgaricus in different of initial
pH.
CONCLUSION
A pH range of 6.5 – 7.5 was the
optimal one for EPS production by L. bulgaricus ropy strain when growing in
SMR 10% at 30oC at 16 h of incubation.
ACKNOWLEDGEMENTS
This
study was partially supported by Hibah Bersaing, DIKTI. Jakarta.
REFERENCES
Chervaux, C., S.D. Ehrlich, and E. Maguin. 2000.
Physiological study of
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(12) : 5306 – 5311.
Grobben, G.J., I.Chin-Joe, V.A. Kizen, I.C. Boels, F.
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and J.A.M. de Bont. 1998.
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Malaka, R. 1997. The effect of Curdlan, a bacteria
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Oliver, G. F. Fe Valdez. 1994.
Effect of pH on the growth
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Dipublikasi di Buletin Penelitian (Seri Hayati) 10 (1): 36 - 40.
Dikirim pada :
Jurnal
Penelitian dan Pengembangan Pertanian
