Food-Microbiology Emerging fermentation technologies Development of novels our doughs Biotechnology Engineering (BT) Notes | EduRev

Biotechnology Engineering (BT) : Food-Microbiology Emerging fermentation technologies Development of novels our doughs Biotechnology Engineering (BT) Notes | EduRev

 Page 1


FOOD
MICROBIOLOGY
Food Microbiology 24 (2007) 155–160
Emergingfermentationtechnologies:Developmentofnovelsourdoughs
G. Lacaze, M. Wick, S. Cappelle

Puratos Group, BU Bio?avors, Industrialaan, 25, 1702 Groot-bijgaarden, Belgium
Abstract
The increasing knowledge of sourdough fermentation generates new opportunities for its use in the bakery ?eld. New fermentation
technologies emerged through in depth sourdough research. Dextrans are extracellular bacterial polysaccharides produced mainly by
lacticacidbacteria(LAB).Thesebacteriaconvertsucrosethankstoaninducibleenzymecalleddextransucraseintodextranandfructose.
The structure of dextran depends on the producing micro-organism and on culture conditions. Depending on its structure, dextran has
speci?cpropertieswhichleadtoseveralindustrialapplicationsindifferentdomains.Theuseofdextranisnotwidelyspreadinthebakery
?eldevenifitsimpactonbreadvolumeandtexturewasshown.Anewprocesshasbeendevelopedtoobtainasourdoughrichindextran
using a speci?c LAB strain able to produce a suf?cient amount of HMW dextran assuring a signi?cant impact on bread volume. The
sourdough obtained permits to improve freshness, crumb structure, mouthfeel and softness of all kinds of baked good from wheat rich
dough products to rye sourdough breads. From fundamental research on dextran technology, a new fermentation process has been
developed to produce an innovative functional ingredient for bakery industry.
r 2006 Published by Elsevier Ltd.
Keywords: Sourdough fermentation; Microbial exopolysaccharides; Dextran; Bread texture
1. Introduction
Sourdough in bakery was traditionally used for its
leavening effect (CO
2
production) and its aromatic impact
on bread (organic acids and volatile compounds). Several
studies on sourdough fermentation and its microbiology
have shown that, besides organic acids and CO
2
, other
kinds of compounds are produced. Indeed, bacteriocins
(Corsetti et al., 2004), antifungal compounds (Lavermi-
cocca et al., 2003) or exo-polysaccharides (Tieking et al.,
2003) are released during the fermentation. Furthermore,
several degradation processes can occur. For example,
Gliadin-like fractions of gluten (Rollan et al., 2005) are
damaged thanks to the microbiological activity. These
researches open new perspectives for the use of sourdough
fermentation in baked products, extending its applications
todomainssuchashealthandpleasure.Thesenew?ndings
lead also to emerging fermentation technologies.
Dextran technology is a good example of such an
emerging fermentation technology. Indeed, from the
isolation of one speci?c strain producing dextran to the
production of sourdoughs based on dextran, a great work
of fermentation development and optimization has been
done.
2. Dextran structure, microbial synthesis and dextran
properties
The term ‘‘dextran’’ is a collective term given to a group
ofbacterialpolysaccharides.Thebasicstructureofdextran
molecules are (1–6) linked a-D-glucopyranosyl residues.
Sometimes, the linear backbone contains branchings at C-
2, C-3, or C-4. Isolated (1–3) linked a-D-glucopyranosyl
residues or sequences of these residues can interrupt the
(1–6) regions. All of the dextrans are more or less rami?ed
(Fig. 1), and the branching very much depends on the
subspecies (Jeans et al., 1954). Most of the branchings are
composed of single a-D-glucopyranosyl residues, although
branchings have been found with 2–50 monomers. Some
branchings are formed by (1–3) linked a-D-glucopyranosyl
residues.Thestructure—suchaslengthofthechain,degree
of branching, type of links—of the dextrans mainly
depends on the producing micro-organism. For example,
ARTICLE IN PRESS
www.elsevier.com/locate/fm
0740-0020/$-see front matterr 2006 Published by Elsevier Ltd.
doi:10.1016/j.fm.2006.07.015

Corresponding author.
E-mail address: scappelle@puratos.com (S. Cappelle).
Page 2


FOOD
MICROBIOLOGY
Food Microbiology 24 (2007) 155–160
Emergingfermentationtechnologies:Developmentofnovelsourdoughs
G. Lacaze, M. Wick, S. Cappelle

Puratos Group, BU Bio?avors, Industrialaan, 25, 1702 Groot-bijgaarden, Belgium
Abstract
The increasing knowledge of sourdough fermentation generates new opportunities for its use in the bakery ?eld. New fermentation
technologies emerged through in depth sourdough research. Dextrans are extracellular bacterial polysaccharides produced mainly by
lacticacidbacteria(LAB).Thesebacteriaconvertsucrosethankstoaninducibleenzymecalleddextransucraseintodextranandfructose.
The structure of dextran depends on the producing micro-organism and on culture conditions. Depending on its structure, dextran has
speci?cpropertieswhichleadtoseveralindustrialapplicationsindifferentdomains.Theuseofdextranisnotwidelyspreadinthebakery
?eldevenifitsimpactonbreadvolumeandtexturewasshown.Anewprocesshasbeendevelopedtoobtainasourdoughrichindextran
using a speci?c LAB strain able to produce a suf?cient amount of HMW dextran assuring a signi?cant impact on bread volume. The
sourdough obtained permits to improve freshness, crumb structure, mouthfeel and softness of all kinds of baked good from wheat rich
dough products to rye sourdough breads. From fundamental research on dextran technology, a new fermentation process has been
developed to produce an innovative functional ingredient for bakery industry.
r 2006 Published by Elsevier Ltd.
Keywords: Sourdough fermentation; Microbial exopolysaccharides; Dextran; Bread texture
1. Introduction
Sourdough in bakery was traditionally used for its
leavening effect (CO
2
production) and its aromatic impact
on bread (organic acids and volatile compounds). Several
studies on sourdough fermentation and its microbiology
have shown that, besides organic acids and CO
2
, other
kinds of compounds are produced. Indeed, bacteriocins
(Corsetti et al., 2004), antifungal compounds (Lavermi-
cocca et al., 2003) or exo-polysaccharides (Tieking et al.,
2003) are released during the fermentation. Furthermore,
several degradation processes can occur. For example,
Gliadin-like fractions of gluten (Rollan et al., 2005) are
damaged thanks to the microbiological activity. These
researches open new perspectives for the use of sourdough
fermentation in baked products, extending its applications
todomainssuchashealthandpleasure.Thesenew?ndings
lead also to emerging fermentation technologies.
Dextran technology is a good example of such an
emerging fermentation technology. Indeed, from the
isolation of one speci?c strain producing dextran to the
production of sourdoughs based on dextran, a great work
of fermentation development and optimization has been
done.
2. Dextran structure, microbial synthesis and dextran
properties
The term ‘‘dextran’’ is a collective term given to a group
ofbacterialpolysaccharides.Thebasicstructureofdextran
molecules are (1–6) linked a-D-glucopyranosyl residues.
Sometimes, the linear backbone contains branchings at C-
2, C-3, or C-4. Isolated (1–3) linked a-D-glucopyranosyl
residues or sequences of these residues can interrupt the
(1–6) regions. All of the dextrans are more or less rami?ed
(Fig. 1), and the branching very much depends on the
subspecies (Jeans et al., 1954). Most of the branchings are
composed of single a-D-glucopyranosyl residues, although
branchings have been found with 2–50 monomers. Some
branchings are formed by (1–3) linked a-D-glucopyranosyl
residues.Thestructure—suchaslengthofthechain,degree
of branching, type of links—of the dextrans mainly
depends on the producing micro-organism. For example,
ARTICLE IN PRESS
www.elsevier.com/locate/fm
0740-0020/$-see front matterr 2006 Published by Elsevier Ltd.
doi:10.1016/j.fm.2006.07.015

Corresponding author.
E-mail address: scappelle@puratos.com (S. Cappelle).
Leuconostoc mesenteroides NRRL B512(F) produces dex-
tran containing 95% of a-1,6 bonds and 5% of a-1,3
bonds. Dextrans are synthesized from sucrose through the
production of an inducible dextransucrase (1,6-a-D-glucan
6-a-D-glucosyltransferase, EC.2.4.1.5). This enzyme, usual-
ly extracellular, is produced from a variety of different
micro-organisms. These bacteria mainly belong to the
group of lactic acid bacteria, and more speci?cally to the
speciesofthe Lactobacillus, Leuconostocand Streptococcus
genus. Certain bacterial strains have been shown to
produce dextrans of various structures, and this was
attributed to the excretion by the micro-organism of
different dextransucrases (Coˆte´ and Robyt, 1982). Dex-
trans can also be synthesized by means of dextrine
dextranase of, for instance, Acetobacter capsulatus ATCC
11894 (Yamamoto et al., 1993). Most microbial polysac-
charides are the products of intracellular catabolic conver-
sion of substrate to intermediates and ?nally to polymer.
For dextrans, this is not the case. Indeed, the substrate,
sucrose, does not enter the micro-organism cell. In excess
of sucrose, the cell release dextransucrase which converts
sucrose to dextran and fructose as shown in Fig. 2. During
theenzymicreaction,dextranislinkedtotheenzymeatthe
reduction end and glucose units are added at the reducing
end by insertion between the dextransucrase and the
growing dextran chain (Robyt et al., 1974).When sucrose
is depleted, the bacteria consume the fructose which has
been accumulated during the polymerization process
(Neely and Nott, 1962). Dextransucrase catalyses the
transfer of the glucosyl unit of sucrose to different
‘‘acceptor molecules’’ which are normally the growing
dextran chain. When another substrate acceptor is also
present, oligosaccharides are produced and part of the
glucosyl moieties from glucose is consumed to form these
acceptor products (Robyt and Walseth, 1978), decreasing
the dextran yield. Thus, as the ratio of acceptor to sucrose
increases, the proportion of dextran decreases and that
of oligosaccharides increases. Over thirty different
carbohydrates are known to act as acceptors of varying
activities (Robyt and Eklund, 1982). The most ef?cient
acceptor molecule is maltose followed in order by
isomaltose, nigerose, a-methyl-D-glucopyranoside and D-
glucose.Inpresenceofmaltose,dextransucrasesynthesized
panose (6,2-a-D-glucopyranosyl maltose) and a homolo-
gous series of 6,2-isomaltodextrinosyl maltoses (Fu and
Robyt, 1990).
Dextrans molecular weights range from 1.510
4
to
210
7
and even higher. The molecular weight of the
dextran can be affected by the presence of acceptors (as
explained above). Temperature, sucrose concentration and
enzyme concentration have also been reported as affecting
the molecular weight of dextran (Tsuchiya et al., 1952).
Thus, at low sucrose concentrations (10%), dextrans of
high molecular weight are formed (410
8
daltons). Dex-
trans solubility depends on their branched structure.
Soluble dextrans are composed of sequences of (1–6)
linked a-D-glucopyranosyl residues, on which, at irregular
intervals, branchings of single a-D-glucopyranosyl residues
are substituted. Insoluble dextrans are more complex and
they often contain more (1–3) linked a-D-glucopyranosyl
sequences. Dextrans form viscous solutions. These solu-
tions show a Newtonian behaviour when concentrations
o30% w/w for low molecular weight dextrans. Dextrans
with a higher molecular weight show a slightly pseudo-
plastic behaviour when concentrations41.5% w/w. There
are no single correlations between the viscosity of dextrans
solution and its branchings. The viscosity enhancing effect
is due to a combination of structure (more or less
branched) and molecular weight (Jeans et al., 1954).
3. Industrial use of dextran
The main applications for dextran are in the pharma-
ceutical and medical sectors. The low molecular weight
dextran is used as a blood plasma substitute as solutions
containing 6% of these dextrans have viscosity value
similar to human blood plasma. Moreover, derivatives of
dextran, like dextran sulfate, are used as a substitute for
heparin. Sephadex, which is a commercial gel ?ltration
material, is made of epichlorohydrin cross-linked dextran.
Although dextran can be used in food products as a
conditioner,stabilizer,or‘‘bodyingagent’’,itisrareto?nd
itasacommercialproductinthefoodindustry.Theuseof
dextrans in the ?eld of bakery is not widely spread,
although a number of applications have been described.
For example, the US Patent 2983613 (Bohn, 1961)
describes the incorporation of a suf?cient amount of
dextrans in bakery products to soften the gluten content
and to increase the speci?c volume. This document
describes that the bread which contains dextran was about
20% bigger in volume than products which do not contain
dextrans. In this particular example, said dextrans are
prepared by growing the micro-organism Leuconostoc
mesenteroides B512, resulting in dextrans having a mole-
cular weight from about 210
6
to about 410
6
daltons.
ARTICLE IN PRESS
Fig. 1. Structure of fragment of dextran molecule.
nC
12
H
22
O
11
   (C
6
H
10
O
5
)n + nC
6
H
12
O
6
sucrose   dextran  fructose
Fig. 2. The conversion of sucrose to dextran by dextransucrase.
G. Lacaze et al. / Food Microbiology 24 (2007) 155–160 156
Page 3


FOOD
MICROBIOLOGY
Food Microbiology 24 (2007) 155–160
Emergingfermentationtechnologies:Developmentofnovelsourdoughs
G. Lacaze, M. Wick, S. Cappelle

Puratos Group, BU Bio?avors, Industrialaan, 25, 1702 Groot-bijgaarden, Belgium
Abstract
The increasing knowledge of sourdough fermentation generates new opportunities for its use in the bakery ?eld. New fermentation
technologies emerged through in depth sourdough research. Dextrans are extracellular bacterial polysaccharides produced mainly by
lacticacidbacteria(LAB).Thesebacteriaconvertsucrosethankstoaninducibleenzymecalleddextransucraseintodextranandfructose.
The structure of dextran depends on the producing micro-organism and on culture conditions. Depending on its structure, dextran has
speci?cpropertieswhichleadtoseveralindustrialapplicationsindifferentdomains.Theuseofdextranisnotwidelyspreadinthebakery
?eldevenifitsimpactonbreadvolumeandtexturewasshown.Anewprocesshasbeendevelopedtoobtainasourdoughrichindextran
using a speci?c LAB strain able to produce a suf?cient amount of HMW dextran assuring a signi?cant impact on bread volume. The
sourdough obtained permits to improve freshness, crumb structure, mouthfeel and softness of all kinds of baked good from wheat rich
dough products to rye sourdough breads. From fundamental research on dextran technology, a new fermentation process has been
developed to produce an innovative functional ingredient for bakery industry.
r 2006 Published by Elsevier Ltd.
Keywords: Sourdough fermentation; Microbial exopolysaccharides; Dextran; Bread texture
1. Introduction
Sourdough in bakery was traditionally used for its
leavening effect (CO
2
production) and its aromatic impact
on bread (organic acids and volatile compounds). Several
studies on sourdough fermentation and its microbiology
have shown that, besides organic acids and CO
2
, other
kinds of compounds are produced. Indeed, bacteriocins
(Corsetti et al., 2004), antifungal compounds (Lavermi-
cocca et al., 2003) or exo-polysaccharides (Tieking et al.,
2003) are released during the fermentation. Furthermore,
several degradation processes can occur. For example,
Gliadin-like fractions of gluten (Rollan et al., 2005) are
damaged thanks to the microbiological activity. These
researches open new perspectives for the use of sourdough
fermentation in baked products, extending its applications
todomainssuchashealthandpleasure.Thesenew?ndings
lead also to emerging fermentation technologies.
Dextran technology is a good example of such an
emerging fermentation technology. Indeed, from the
isolation of one speci?c strain producing dextran to the
production of sourdoughs based on dextran, a great work
of fermentation development and optimization has been
done.
2. Dextran structure, microbial synthesis and dextran
properties
The term ‘‘dextran’’ is a collective term given to a group
ofbacterialpolysaccharides.Thebasicstructureofdextran
molecules are (1–6) linked a-D-glucopyranosyl residues.
Sometimes, the linear backbone contains branchings at C-
2, C-3, or C-4. Isolated (1–3) linked a-D-glucopyranosyl
residues or sequences of these residues can interrupt the
(1–6) regions. All of the dextrans are more or less rami?ed
(Fig. 1), and the branching very much depends on the
subspecies (Jeans et al., 1954). Most of the branchings are
composed of single a-D-glucopyranosyl residues, although
branchings have been found with 2–50 monomers. Some
branchings are formed by (1–3) linked a-D-glucopyranosyl
residues.Thestructure—suchaslengthofthechain,degree
of branching, type of links—of the dextrans mainly
depends on the producing micro-organism. For example,
ARTICLE IN PRESS
www.elsevier.com/locate/fm
0740-0020/$-see front matterr 2006 Published by Elsevier Ltd.
doi:10.1016/j.fm.2006.07.015

Corresponding author.
E-mail address: scappelle@puratos.com (S. Cappelle).
Leuconostoc mesenteroides NRRL B512(F) produces dex-
tran containing 95% of a-1,6 bonds and 5% of a-1,3
bonds. Dextrans are synthesized from sucrose through the
production of an inducible dextransucrase (1,6-a-D-glucan
6-a-D-glucosyltransferase, EC.2.4.1.5). This enzyme, usual-
ly extracellular, is produced from a variety of different
micro-organisms. These bacteria mainly belong to the
group of lactic acid bacteria, and more speci?cally to the
speciesofthe Lactobacillus, Leuconostocand Streptococcus
genus. Certain bacterial strains have been shown to
produce dextrans of various structures, and this was
attributed to the excretion by the micro-organism of
different dextransucrases (Coˆte´ and Robyt, 1982). Dex-
trans can also be synthesized by means of dextrine
dextranase of, for instance, Acetobacter capsulatus ATCC
11894 (Yamamoto et al., 1993). Most microbial polysac-
charides are the products of intracellular catabolic conver-
sion of substrate to intermediates and ?nally to polymer.
For dextrans, this is not the case. Indeed, the substrate,
sucrose, does not enter the micro-organism cell. In excess
of sucrose, the cell release dextransucrase which converts
sucrose to dextran and fructose as shown in Fig. 2. During
theenzymicreaction,dextranislinkedtotheenzymeatthe
reduction end and glucose units are added at the reducing
end by insertion between the dextransucrase and the
growing dextran chain (Robyt et al., 1974).When sucrose
is depleted, the bacteria consume the fructose which has
been accumulated during the polymerization process
(Neely and Nott, 1962). Dextransucrase catalyses the
transfer of the glucosyl unit of sucrose to different
‘‘acceptor molecules’’ which are normally the growing
dextran chain. When another substrate acceptor is also
present, oligosaccharides are produced and part of the
glucosyl moieties from glucose is consumed to form these
acceptor products (Robyt and Walseth, 1978), decreasing
the dextran yield. Thus, as the ratio of acceptor to sucrose
increases, the proportion of dextran decreases and that
of oligosaccharides increases. Over thirty different
carbohydrates are known to act as acceptors of varying
activities (Robyt and Eklund, 1982). The most ef?cient
acceptor molecule is maltose followed in order by
isomaltose, nigerose, a-methyl-D-glucopyranoside and D-
glucose.Inpresenceofmaltose,dextransucrasesynthesized
panose (6,2-a-D-glucopyranosyl maltose) and a homolo-
gous series of 6,2-isomaltodextrinosyl maltoses (Fu and
Robyt, 1990).
Dextrans molecular weights range from 1.510
4
to
210
7
and even higher. The molecular weight of the
dextran can be affected by the presence of acceptors (as
explained above). Temperature, sucrose concentration and
enzyme concentration have also been reported as affecting
the molecular weight of dextran (Tsuchiya et al., 1952).
Thus, at low sucrose concentrations (10%), dextrans of
high molecular weight are formed (410
8
daltons). Dex-
trans solubility depends on their branched structure.
Soluble dextrans are composed of sequences of (1–6)
linked a-D-glucopyranosyl residues, on which, at irregular
intervals, branchings of single a-D-glucopyranosyl residues
are substituted. Insoluble dextrans are more complex and
they often contain more (1–3) linked a-D-glucopyranosyl
sequences. Dextrans form viscous solutions. These solu-
tions show a Newtonian behaviour when concentrations
o30% w/w for low molecular weight dextrans. Dextrans
with a higher molecular weight show a slightly pseudo-
plastic behaviour when concentrations41.5% w/w. There
are no single correlations between the viscosity of dextrans
solution and its branchings. The viscosity enhancing effect
is due to a combination of structure (more or less
branched) and molecular weight (Jeans et al., 1954).
3. Industrial use of dextran
The main applications for dextran are in the pharma-
ceutical and medical sectors. The low molecular weight
dextran is used as a blood plasma substitute as solutions
containing 6% of these dextrans have viscosity value
similar to human blood plasma. Moreover, derivatives of
dextran, like dextran sulfate, are used as a substitute for
heparin. Sephadex, which is a commercial gel ?ltration
material, is made of epichlorohydrin cross-linked dextran.
Although dextran can be used in food products as a
conditioner,stabilizer,or‘‘bodyingagent’’,itisrareto?nd
itasacommercialproductinthefoodindustry.Theuseof
dextrans in the ?eld of bakery is not widely spread,
although a number of applications have been described.
For example, the US Patent 2983613 (Bohn, 1961)
describes the incorporation of a suf?cient amount of
dextrans in bakery products to soften the gluten content
and to increase the speci?c volume. This document
describes that the bread which contains dextran was about
20% bigger in volume than products which do not contain
dextrans. In this particular example, said dextrans are
prepared by growing the micro-organism Leuconostoc
mesenteroides B512, resulting in dextrans having a mole-
cular weight from about 210
6
to about 410
6
daltons.
ARTICLE IN PRESS
Fig. 1. Structure of fragment of dextran molecule.
nC
12
H
22
O
11
   (C
6
H
10
O
5
)n + nC
6
H
12
O
6
sucrose   dextran  fructose
Fig. 2. The conversion of sucrose to dextran by dextransucrase.
G. Lacaze et al. / Food Microbiology 24 (2007) 155–160 156
According to these facts, it has been decided to develop
sourdoughsbasedondextraninordertoproposetobakers
a solution to improve texture/volume of their baking
products.
4. Industrial technology for producing dextran based
sourdoughs
The ?rst step consisted in selecting a strain able to
produce suf?cient amounts of dextran to get a positive
impact on bread quality. Strains were ?rst isolated from
sourdoughs and cultured milk products and then selected
on solid modi?ed MRS medium supplemented with
sucrose (4%). Ropy colonies were retained for dextran
productionwhichwasdoneintwostepsapproach:enzyme
production then bioconversion. This 2 steps process
consisted in applying different sucrose concentrations and
pH. A strain, isolated from a natural sourdough system
(Panettone) and identi?ed as a L. mesenteroides spp. was
selected. This strain (deposit number LMGP-16878)
produces a dextran which gave signi?cant volume im-
provement in wheat bread baking trials compared to guar
and dextran from L. mesenteroides B512F (Table 1). These
results clearly show that the type and the origin of the
polymer is critical. The dextran synthesized by the strain
LMGP-16878 is characterized by its structure—95.4% of
a-1,6 bonds and 4.6% of a-1,3 bonds—and its high
molecular weight. These data show that dextran with a
high molecular weight and a linear chain structure is more
ef?cient on bread volume than dextran with a high
molecular weight and more branching. The second step
wastodevelopaspeci?csourdoughfermentationusingthe
strain selected ?rst, in order to obtain effective amount of
dextraninthesourdough.Thesesourdoughs,onebasedon
wheat ?our and the other based on rye ?our, are obtained
by the fermentation of ?our and sucrose by L. mesenter-
oidesLMGP-16878.Thefermentation,carriedoutat251C,
is produced in two stages. The ?rst stage consists in the
production of the starter culture L. mesenteroides LMGP-
16878 on an adapted growth medium. In a second stage,
doughcomposedof?our,waterandsucroseisstartedwith
the strain LMGP-16878 and fermented at 251C. The
optimum sucrose concentration and fermentation process
parameters were determined. During fermentation, the pH
drops naturallythroughthe organicacid productionofthe
strain, passing all pH levels of enzyme induction, biocon-
version and fermentation of residual fructose (Lazic et al.,
1993; Tsuchiya et al., 1952). The increase of dough
viscosity during this step demonstrates the production of
dextran. The ?nal wheat sourdough is characterized by a
pHcomprisedbetween3.5and3.9,anacidityaround40ml
of NaOH
0,1N
/10g, and a viscosity between 4000 and
5500cp. The rye sourdough has a pH between 3.2 and
3.6 and an acidity around 49ml of NaOH
0.1N
/10g. These
sourdoughs are used at a level of 10% on ?our weight and
improve volume and texture of the baked products.
5. Applications of dextran in bakery
The advantages of this speci?c type of dextran and the
dextran containing sourdoughs in bakery applications are
multiple. More water can be bound in the dough: as
dextran is a hydrocolloid, it can bind high amounts of
water. Higher dough yield often leads to an improved
freshness of the end product. Dextran improves dough
stability and gas retention through a structure build up of
thedextransandinteractionwithglutennetwork.InFig.3,
itisclearlyshownthatdextransbuildupacertainstructure
when a shear force is applied on a1% solution. This is not
the case with the well-known gums like guar and xanthan.
This is probably explained by the fact that the long linear
dextran molecules line up very well and hydrogen interac-
tions occur. The oven jump is signi?cantly better after
addition of dextran. This can also be explained due to the
improved dough stability and gas retention. The crumb
structure is altered. Thegas bubbles are more long shaped,
typical for long fermentation processes. Mouthfeel is
improved: a moister mouthfeel is obtained by addition of
dextran.
The effect becomes even clearer the longer the bread is
conserved. In a lot of applications, a very short bite can
also be experienced after addition of a dextran containing
sourdough. The softness of the bread crumb is measured
ARTICLE IN PRESS
Table 1
Effectof additionof dextransproducedby different strainson ?nalbread
volume and comparison with guar gum (European patent EP 0 790 003
B1)
Volume increase compared
to reference (vol%)
Reference+0.5% guar 10
Reference+1% guar 5
Reference+0.5% dextrans B512F 8
Reference+1% dextrans B512F 12
Reference+0.5% dextrans LMGP-
16878
18
Reference+1% dextrans LMGP-16878 32
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
2 9 7 4 1114161921232628
time (minutes)
viscosity (Pa.s)
guar
xanthan
dextran
Fig. 3. Improved dough stability due to structure build up of dextran.
G. Lacaze et al. / Food Microbiology 24 (2007) 155–160 157
Page 4


FOOD
MICROBIOLOGY
Food Microbiology 24 (2007) 155–160
Emergingfermentationtechnologies:Developmentofnovelsourdoughs
G. Lacaze, M. Wick, S. Cappelle

Puratos Group, BU Bio?avors, Industrialaan, 25, 1702 Groot-bijgaarden, Belgium
Abstract
The increasing knowledge of sourdough fermentation generates new opportunities for its use in the bakery ?eld. New fermentation
technologies emerged through in depth sourdough research. Dextrans are extracellular bacterial polysaccharides produced mainly by
lacticacidbacteria(LAB).Thesebacteriaconvertsucrosethankstoaninducibleenzymecalleddextransucraseintodextranandfructose.
The structure of dextran depends on the producing micro-organism and on culture conditions. Depending on its structure, dextran has
speci?cpropertieswhichleadtoseveralindustrialapplicationsindifferentdomains.Theuseofdextranisnotwidelyspreadinthebakery
?eldevenifitsimpactonbreadvolumeandtexturewasshown.Anewprocesshasbeendevelopedtoobtainasourdoughrichindextran
using a speci?c LAB strain able to produce a suf?cient amount of HMW dextran assuring a signi?cant impact on bread volume. The
sourdough obtained permits to improve freshness, crumb structure, mouthfeel and softness of all kinds of baked good from wheat rich
dough products to rye sourdough breads. From fundamental research on dextran technology, a new fermentation process has been
developed to produce an innovative functional ingredient for bakery industry.
r 2006 Published by Elsevier Ltd.
Keywords: Sourdough fermentation; Microbial exopolysaccharides; Dextran; Bread texture
1. Introduction
Sourdough in bakery was traditionally used for its
leavening effect (CO
2
production) and its aromatic impact
on bread (organic acids and volatile compounds). Several
studies on sourdough fermentation and its microbiology
have shown that, besides organic acids and CO
2
, other
kinds of compounds are produced. Indeed, bacteriocins
(Corsetti et al., 2004), antifungal compounds (Lavermi-
cocca et al., 2003) or exo-polysaccharides (Tieking et al.,
2003) are released during the fermentation. Furthermore,
several degradation processes can occur. For example,
Gliadin-like fractions of gluten (Rollan et al., 2005) are
damaged thanks to the microbiological activity. These
researches open new perspectives for the use of sourdough
fermentation in baked products, extending its applications
todomainssuchashealthandpleasure.Thesenew?ndings
lead also to emerging fermentation technologies.
Dextran technology is a good example of such an
emerging fermentation technology. Indeed, from the
isolation of one speci?c strain producing dextran to the
production of sourdoughs based on dextran, a great work
of fermentation development and optimization has been
done.
2. Dextran structure, microbial synthesis and dextran
properties
The term ‘‘dextran’’ is a collective term given to a group
ofbacterialpolysaccharides.Thebasicstructureofdextran
molecules are (1–6) linked a-D-glucopyranosyl residues.
Sometimes, the linear backbone contains branchings at C-
2, C-3, or C-4. Isolated (1–3) linked a-D-glucopyranosyl
residues or sequences of these residues can interrupt the
(1–6) regions. All of the dextrans are more or less rami?ed
(Fig. 1), and the branching very much depends on the
subspecies (Jeans et al., 1954). Most of the branchings are
composed of single a-D-glucopyranosyl residues, although
branchings have been found with 2–50 monomers. Some
branchings are formed by (1–3) linked a-D-glucopyranosyl
residues.Thestructure—suchaslengthofthechain,degree
of branching, type of links—of the dextrans mainly
depends on the producing micro-organism. For example,
ARTICLE IN PRESS
www.elsevier.com/locate/fm
0740-0020/$-see front matterr 2006 Published by Elsevier Ltd.
doi:10.1016/j.fm.2006.07.015

Corresponding author.
E-mail address: scappelle@puratos.com (S. Cappelle).
Leuconostoc mesenteroides NRRL B512(F) produces dex-
tran containing 95% of a-1,6 bonds and 5% of a-1,3
bonds. Dextrans are synthesized from sucrose through the
production of an inducible dextransucrase (1,6-a-D-glucan
6-a-D-glucosyltransferase, EC.2.4.1.5). This enzyme, usual-
ly extracellular, is produced from a variety of different
micro-organisms. These bacteria mainly belong to the
group of lactic acid bacteria, and more speci?cally to the
speciesofthe Lactobacillus, Leuconostocand Streptococcus
genus. Certain bacterial strains have been shown to
produce dextrans of various structures, and this was
attributed to the excretion by the micro-organism of
different dextransucrases (Coˆte´ and Robyt, 1982). Dex-
trans can also be synthesized by means of dextrine
dextranase of, for instance, Acetobacter capsulatus ATCC
11894 (Yamamoto et al., 1993). Most microbial polysac-
charides are the products of intracellular catabolic conver-
sion of substrate to intermediates and ?nally to polymer.
For dextrans, this is not the case. Indeed, the substrate,
sucrose, does not enter the micro-organism cell. In excess
of sucrose, the cell release dextransucrase which converts
sucrose to dextran and fructose as shown in Fig. 2. During
theenzymicreaction,dextranislinkedtotheenzymeatthe
reduction end and glucose units are added at the reducing
end by insertion between the dextransucrase and the
growing dextran chain (Robyt et al., 1974).When sucrose
is depleted, the bacteria consume the fructose which has
been accumulated during the polymerization process
(Neely and Nott, 1962). Dextransucrase catalyses the
transfer of the glucosyl unit of sucrose to different
‘‘acceptor molecules’’ which are normally the growing
dextran chain. When another substrate acceptor is also
present, oligosaccharides are produced and part of the
glucosyl moieties from glucose is consumed to form these
acceptor products (Robyt and Walseth, 1978), decreasing
the dextran yield. Thus, as the ratio of acceptor to sucrose
increases, the proportion of dextran decreases and that
of oligosaccharides increases. Over thirty different
carbohydrates are known to act as acceptors of varying
activities (Robyt and Eklund, 1982). The most ef?cient
acceptor molecule is maltose followed in order by
isomaltose, nigerose, a-methyl-D-glucopyranoside and D-
glucose.Inpresenceofmaltose,dextransucrasesynthesized
panose (6,2-a-D-glucopyranosyl maltose) and a homolo-
gous series of 6,2-isomaltodextrinosyl maltoses (Fu and
Robyt, 1990).
Dextrans molecular weights range from 1.510
4
to
210
7
and even higher. The molecular weight of the
dextran can be affected by the presence of acceptors (as
explained above). Temperature, sucrose concentration and
enzyme concentration have also been reported as affecting
the molecular weight of dextran (Tsuchiya et al., 1952).
Thus, at low sucrose concentrations (10%), dextrans of
high molecular weight are formed (410
8
daltons). Dex-
trans solubility depends on their branched structure.
Soluble dextrans are composed of sequences of (1–6)
linked a-D-glucopyranosyl residues, on which, at irregular
intervals, branchings of single a-D-glucopyranosyl residues
are substituted. Insoluble dextrans are more complex and
they often contain more (1–3) linked a-D-glucopyranosyl
sequences. Dextrans form viscous solutions. These solu-
tions show a Newtonian behaviour when concentrations
o30% w/w for low molecular weight dextrans. Dextrans
with a higher molecular weight show a slightly pseudo-
plastic behaviour when concentrations41.5% w/w. There
are no single correlations between the viscosity of dextrans
solution and its branchings. The viscosity enhancing effect
is due to a combination of structure (more or less
branched) and molecular weight (Jeans et al., 1954).
3. Industrial use of dextran
The main applications for dextran are in the pharma-
ceutical and medical sectors. The low molecular weight
dextran is used as a blood plasma substitute as solutions
containing 6% of these dextrans have viscosity value
similar to human blood plasma. Moreover, derivatives of
dextran, like dextran sulfate, are used as a substitute for
heparin. Sephadex, which is a commercial gel ?ltration
material, is made of epichlorohydrin cross-linked dextran.
Although dextran can be used in food products as a
conditioner,stabilizer,or‘‘bodyingagent’’,itisrareto?nd
itasacommercialproductinthefoodindustry.Theuseof
dextrans in the ?eld of bakery is not widely spread,
although a number of applications have been described.
For example, the US Patent 2983613 (Bohn, 1961)
describes the incorporation of a suf?cient amount of
dextrans in bakery products to soften the gluten content
and to increase the speci?c volume. This document
describes that the bread which contains dextran was about
20% bigger in volume than products which do not contain
dextrans. In this particular example, said dextrans are
prepared by growing the micro-organism Leuconostoc
mesenteroides B512, resulting in dextrans having a mole-
cular weight from about 210
6
to about 410
6
daltons.
ARTICLE IN PRESS
Fig. 1. Structure of fragment of dextran molecule.
nC
12
H
22
O
11
   (C
6
H
10
O
5
)n + nC
6
H
12
O
6
sucrose   dextran  fructose
Fig. 2. The conversion of sucrose to dextran by dextransucrase.
G. Lacaze et al. / Food Microbiology 24 (2007) 155–160 156
According to these facts, it has been decided to develop
sourdoughsbasedondextraninordertoproposetobakers
a solution to improve texture/volume of their baking
products.
4. Industrial technology for producing dextran based
sourdoughs
The ?rst step consisted in selecting a strain able to
produce suf?cient amounts of dextran to get a positive
impact on bread quality. Strains were ?rst isolated from
sourdoughs and cultured milk products and then selected
on solid modi?ed MRS medium supplemented with
sucrose (4%). Ropy colonies were retained for dextran
productionwhichwasdoneintwostepsapproach:enzyme
production then bioconversion. This 2 steps process
consisted in applying different sucrose concentrations and
pH. A strain, isolated from a natural sourdough system
(Panettone) and identi?ed as a L. mesenteroides spp. was
selected. This strain (deposit number LMGP-16878)
produces a dextran which gave signi?cant volume im-
provement in wheat bread baking trials compared to guar
and dextran from L. mesenteroides B512F (Table 1). These
results clearly show that the type and the origin of the
polymer is critical. The dextran synthesized by the strain
LMGP-16878 is characterized by its structure—95.4% of
a-1,6 bonds and 4.6% of a-1,3 bonds—and its high
molecular weight. These data show that dextran with a
high molecular weight and a linear chain structure is more
ef?cient on bread volume than dextran with a high
molecular weight and more branching. The second step
wastodevelopaspeci?csourdoughfermentationusingthe
strain selected ?rst, in order to obtain effective amount of
dextraninthesourdough.Thesesourdoughs,onebasedon
wheat ?our and the other based on rye ?our, are obtained
by the fermentation of ?our and sucrose by L. mesenter-
oidesLMGP-16878.Thefermentation,carriedoutat251C,
is produced in two stages. The ?rst stage consists in the
production of the starter culture L. mesenteroides LMGP-
16878 on an adapted growth medium. In a second stage,
doughcomposedof?our,waterandsucroseisstartedwith
the strain LMGP-16878 and fermented at 251C. The
optimum sucrose concentration and fermentation process
parameters were determined. During fermentation, the pH
drops naturallythroughthe organicacid productionofthe
strain, passing all pH levels of enzyme induction, biocon-
version and fermentation of residual fructose (Lazic et al.,
1993; Tsuchiya et al., 1952). The increase of dough
viscosity during this step demonstrates the production of
dextran. The ?nal wheat sourdough is characterized by a
pHcomprisedbetween3.5and3.9,anacidityaround40ml
of NaOH
0,1N
/10g, and a viscosity between 4000 and
5500cp. The rye sourdough has a pH between 3.2 and
3.6 and an acidity around 49ml of NaOH
0.1N
/10g. These
sourdoughs are used at a level of 10% on ?our weight and
improve volume and texture of the baked products.
5. Applications of dextran in bakery
The advantages of this speci?c type of dextran and the
dextran containing sourdoughs in bakery applications are
multiple. More water can be bound in the dough: as
dextran is a hydrocolloid, it can bind high amounts of
water. Higher dough yield often leads to an improved
freshness of the end product. Dextran improves dough
stability and gas retention through a structure build up of
thedextransandinteractionwithglutennetwork.InFig.3,
itisclearlyshownthatdextransbuildupacertainstructure
when a shear force is applied on a1% solution. This is not
the case with the well-known gums like guar and xanthan.
This is probably explained by the fact that the long linear
dextran molecules line up very well and hydrogen interac-
tions occur. The oven jump is signi?cantly better after
addition of dextran. This can also be explained due to the
improved dough stability and gas retention. The crumb
structure is altered. Thegas bubbles are more long shaped,
typical for long fermentation processes. Mouthfeel is
improved: a moister mouthfeel is obtained by addition of
dextran.
The effect becomes even clearer the longer the bread is
conserved. In a lot of applications, a very short bite can
also be experienced after addition of a dextran containing
sourdough. The softness of the bread crumb is measured
ARTICLE IN PRESS
Table 1
Effectof additionof dextransproducedby different strainson ?nalbread
volume and comparison with guar gum (European patent EP 0 790 003
B1)
Volume increase compared
to reference (vol%)
Reference+0.5% guar 10
Reference+1% guar 5
Reference+0.5% dextrans B512F 8
Reference+1% dextrans B512F 12
Reference+0.5% dextrans LMGP-
16878
18
Reference+1% dextrans LMGP-16878 32
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
2 9 7 4 1114161921232628
time (minutes)
viscosity (Pa.s)
guar
xanthan
dextran
Fig. 3. Improved dough stability due to structure build up of dextran.
G. Lacaze et al. / Food Microbiology 24 (2007) 155–160 157
with a texture analyzer. All of these advantages are
described in the patent EP0790003B1 (Vandamme et al.,
1997). The application ?elds of dextran containing
sourdoughs are multiple: from rich wheat doughs (fat,
sugar) up to very heavy rye dough systems (rye breads).
In viennoiserie, the effect of addition of sourdough has
been evaluated in industrial trials (milk bread application).
Reference milk bread (without sourdough) has been
compared with a milk bread containing 5% of a liquid
active wheat sourdough based on dextran. After 2 weeks
conservation, hardness, pH and water activity have been
measured. It has been shown that hardness was signi?-
cantly reduced with liquid wheat dextran sourdough
(Fig. 4). pH of milk bread crumb was reduced by 0.3 units
with the addition of sourdough. Water activity was
identical. A panel test run on 40 people showed that the
milk bread that contained dextran sourdough was sig-
ni?cantlypreferredtothereference.Moreover,aconsumer
panel test hasbeen run on 205 persons in Nantes(France).
Those people were chosen at the exit of a supermarket but
no selection was done on people (age, profession, etc.).
Butter brioches containing wheat dextran sourdough were
compared with brioches without, in a preference tests.
People were asked to rank the product in terms of general
preference,bygivingascorefrom1to10.Thesumofrank
is calculated at the number of people multiplied by the
ARTICLE IN PRESS
0 
100 
200 
300 
400 
500 
600 
700 
800 
Hardness (g)
Essais 747 569
REFERENCE  WITHOUT  SOURDOUGH 5% LIQUID WHEAT SOURDOUGH BASED ON DEXTRAN
Fig. 4. Effect of liquid dextran wheat sourdough on hardness of milk bread after 2 weeks conservation.
460
470
480
490
500
510
520
530
540
550
Sum of ranking
Sum of ranking 492 546
Butter brioche Butter brioche with 5% dextran sourdough
Fig. 5. Effect of dextran sourdough addition in butter brioches on consumers’ preferences.
G. Lacaze et al. / Food Microbiology 24 (2007) 155–160 158
Page 5


FOOD
MICROBIOLOGY
Food Microbiology 24 (2007) 155–160
Emergingfermentationtechnologies:Developmentofnovelsourdoughs
G. Lacaze, M. Wick, S. Cappelle

Puratos Group, BU Bio?avors, Industrialaan, 25, 1702 Groot-bijgaarden, Belgium
Abstract
The increasing knowledge of sourdough fermentation generates new opportunities for its use in the bakery ?eld. New fermentation
technologies emerged through in depth sourdough research. Dextrans are extracellular bacterial polysaccharides produced mainly by
lacticacidbacteria(LAB).Thesebacteriaconvertsucrosethankstoaninducibleenzymecalleddextransucraseintodextranandfructose.
The structure of dextran depends on the producing micro-organism and on culture conditions. Depending on its structure, dextran has
speci?cpropertieswhichleadtoseveralindustrialapplicationsindifferentdomains.Theuseofdextranisnotwidelyspreadinthebakery
?eldevenifitsimpactonbreadvolumeandtexturewasshown.Anewprocesshasbeendevelopedtoobtainasourdoughrichindextran
using a speci?c LAB strain able to produce a suf?cient amount of HMW dextran assuring a signi?cant impact on bread volume. The
sourdough obtained permits to improve freshness, crumb structure, mouthfeel and softness of all kinds of baked good from wheat rich
dough products to rye sourdough breads. From fundamental research on dextran technology, a new fermentation process has been
developed to produce an innovative functional ingredient for bakery industry.
r 2006 Published by Elsevier Ltd.
Keywords: Sourdough fermentation; Microbial exopolysaccharides; Dextran; Bread texture
1. Introduction
Sourdough in bakery was traditionally used for its
leavening effect (CO
2
production) and its aromatic impact
on bread (organic acids and volatile compounds). Several
studies on sourdough fermentation and its microbiology
have shown that, besides organic acids and CO
2
, other
kinds of compounds are produced. Indeed, bacteriocins
(Corsetti et al., 2004), antifungal compounds (Lavermi-
cocca et al., 2003) or exo-polysaccharides (Tieking et al.,
2003) are released during the fermentation. Furthermore,
several degradation processes can occur. For example,
Gliadin-like fractions of gluten (Rollan et al., 2005) are
damaged thanks to the microbiological activity. These
researches open new perspectives for the use of sourdough
fermentation in baked products, extending its applications
todomainssuchashealthandpleasure.Thesenew?ndings
lead also to emerging fermentation technologies.
Dextran technology is a good example of such an
emerging fermentation technology. Indeed, from the
isolation of one speci?c strain producing dextran to the
production of sourdoughs based on dextran, a great work
of fermentation development and optimization has been
done.
2. Dextran structure, microbial synthesis and dextran
properties
The term ‘‘dextran’’ is a collective term given to a group
ofbacterialpolysaccharides.Thebasicstructureofdextran
molecules are (1–6) linked a-D-glucopyranosyl residues.
Sometimes, the linear backbone contains branchings at C-
2, C-3, or C-4. Isolated (1–3) linked a-D-glucopyranosyl
residues or sequences of these residues can interrupt the
(1–6) regions. All of the dextrans are more or less rami?ed
(Fig. 1), and the branching very much depends on the
subspecies (Jeans et al., 1954). Most of the branchings are
composed of single a-D-glucopyranosyl residues, although
branchings have been found with 2–50 monomers. Some
branchings are formed by (1–3) linked a-D-glucopyranosyl
residues.Thestructure—suchaslengthofthechain,degree
of branching, type of links—of the dextrans mainly
depends on the producing micro-organism. For example,
ARTICLE IN PRESS
www.elsevier.com/locate/fm
0740-0020/$-see front matterr 2006 Published by Elsevier Ltd.
doi:10.1016/j.fm.2006.07.015

Corresponding author.
E-mail address: scappelle@puratos.com (S. Cappelle).
Leuconostoc mesenteroides NRRL B512(F) produces dex-
tran containing 95% of a-1,6 bonds and 5% of a-1,3
bonds. Dextrans are synthesized from sucrose through the
production of an inducible dextransucrase (1,6-a-D-glucan
6-a-D-glucosyltransferase, EC.2.4.1.5). This enzyme, usual-
ly extracellular, is produced from a variety of different
micro-organisms. These bacteria mainly belong to the
group of lactic acid bacteria, and more speci?cally to the
speciesofthe Lactobacillus, Leuconostocand Streptococcus
genus. Certain bacterial strains have been shown to
produce dextrans of various structures, and this was
attributed to the excretion by the micro-organism of
different dextransucrases (Coˆte´ and Robyt, 1982). Dex-
trans can also be synthesized by means of dextrine
dextranase of, for instance, Acetobacter capsulatus ATCC
11894 (Yamamoto et al., 1993). Most microbial polysac-
charides are the products of intracellular catabolic conver-
sion of substrate to intermediates and ?nally to polymer.
For dextrans, this is not the case. Indeed, the substrate,
sucrose, does not enter the micro-organism cell. In excess
of sucrose, the cell release dextransucrase which converts
sucrose to dextran and fructose as shown in Fig. 2. During
theenzymicreaction,dextranislinkedtotheenzymeatthe
reduction end and glucose units are added at the reducing
end by insertion between the dextransucrase and the
growing dextran chain (Robyt et al., 1974).When sucrose
is depleted, the bacteria consume the fructose which has
been accumulated during the polymerization process
(Neely and Nott, 1962). Dextransucrase catalyses the
transfer of the glucosyl unit of sucrose to different
‘‘acceptor molecules’’ which are normally the growing
dextran chain. When another substrate acceptor is also
present, oligosaccharides are produced and part of the
glucosyl moieties from glucose is consumed to form these
acceptor products (Robyt and Walseth, 1978), decreasing
the dextran yield. Thus, as the ratio of acceptor to sucrose
increases, the proportion of dextran decreases and that
of oligosaccharides increases. Over thirty different
carbohydrates are known to act as acceptors of varying
activities (Robyt and Eklund, 1982). The most ef?cient
acceptor molecule is maltose followed in order by
isomaltose, nigerose, a-methyl-D-glucopyranoside and D-
glucose.Inpresenceofmaltose,dextransucrasesynthesized
panose (6,2-a-D-glucopyranosyl maltose) and a homolo-
gous series of 6,2-isomaltodextrinosyl maltoses (Fu and
Robyt, 1990).
Dextrans molecular weights range from 1.510
4
to
210
7
and even higher. The molecular weight of the
dextran can be affected by the presence of acceptors (as
explained above). Temperature, sucrose concentration and
enzyme concentration have also been reported as affecting
the molecular weight of dextran (Tsuchiya et al., 1952).
Thus, at low sucrose concentrations (10%), dextrans of
high molecular weight are formed (410
8
daltons). Dex-
trans solubility depends on their branched structure.
Soluble dextrans are composed of sequences of (1–6)
linked a-D-glucopyranosyl residues, on which, at irregular
intervals, branchings of single a-D-glucopyranosyl residues
are substituted. Insoluble dextrans are more complex and
they often contain more (1–3) linked a-D-glucopyranosyl
sequences. Dextrans form viscous solutions. These solu-
tions show a Newtonian behaviour when concentrations
o30% w/w for low molecular weight dextrans. Dextrans
with a higher molecular weight show a slightly pseudo-
plastic behaviour when concentrations41.5% w/w. There
are no single correlations between the viscosity of dextrans
solution and its branchings. The viscosity enhancing effect
is due to a combination of structure (more or less
branched) and molecular weight (Jeans et al., 1954).
3. Industrial use of dextran
The main applications for dextran are in the pharma-
ceutical and medical sectors. The low molecular weight
dextran is used as a blood plasma substitute as solutions
containing 6% of these dextrans have viscosity value
similar to human blood plasma. Moreover, derivatives of
dextran, like dextran sulfate, are used as a substitute for
heparin. Sephadex, which is a commercial gel ?ltration
material, is made of epichlorohydrin cross-linked dextran.
Although dextran can be used in food products as a
conditioner,stabilizer,or‘‘bodyingagent’’,itisrareto?nd
itasacommercialproductinthefoodindustry.Theuseof
dextrans in the ?eld of bakery is not widely spread,
although a number of applications have been described.
For example, the US Patent 2983613 (Bohn, 1961)
describes the incorporation of a suf?cient amount of
dextrans in bakery products to soften the gluten content
and to increase the speci?c volume. This document
describes that the bread which contains dextran was about
20% bigger in volume than products which do not contain
dextrans. In this particular example, said dextrans are
prepared by growing the micro-organism Leuconostoc
mesenteroides B512, resulting in dextrans having a mole-
cular weight from about 210
6
to about 410
6
daltons.
ARTICLE IN PRESS
Fig. 1. Structure of fragment of dextran molecule.
nC
12
H
22
O
11
   (C
6
H
10
O
5
)n + nC
6
H
12
O
6
sucrose   dextran  fructose
Fig. 2. The conversion of sucrose to dextran by dextransucrase.
G. Lacaze et al. / Food Microbiology 24 (2007) 155–160 156
According to these facts, it has been decided to develop
sourdoughsbasedondextraninordertoproposetobakers
a solution to improve texture/volume of their baking
products.
4. Industrial technology for producing dextran based
sourdoughs
The ?rst step consisted in selecting a strain able to
produce suf?cient amounts of dextran to get a positive
impact on bread quality. Strains were ?rst isolated from
sourdoughs and cultured milk products and then selected
on solid modi?ed MRS medium supplemented with
sucrose (4%). Ropy colonies were retained for dextran
productionwhichwasdoneintwostepsapproach:enzyme
production then bioconversion. This 2 steps process
consisted in applying different sucrose concentrations and
pH. A strain, isolated from a natural sourdough system
(Panettone) and identi?ed as a L. mesenteroides spp. was
selected. This strain (deposit number LMGP-16878)
produces a dextran which gave signi?cant volume im-
provement in wheat bread baking trials compared to guar
and dextran from L. mesenteroides B512F (Table 1). These
results clearly show that the type and the origin of the
polymer is critical. The dextran synthesized by the strain
LMGP-16878 is characterized by its structure—95.4% of
a-1,6 bonds and 4.6% of a-1,3 bonds—and its high
molecular weight. These data show that dextran with a
high molecular weight and a linear chain structure is more
ef?cient on bread volume than dextran with a high
molecular weight and more branching. The second step
wastodevelopaspeci?csourdoughfermentationusingthe
strain selected ?rst, in order to obtain effective amount of
dextraninthesourdough.Thesesourdoughs,onebasedon
wheat ?our and the other based on rye ?our, are obtained
by the fermentation of ?our and sucrose by L. mesenter-
oidesLMGP-16878.Thefermentation,carriedoutat251C,
is produced in two stages. The ?rst stage consists in the
production of the starter culture L. mesenteroides LMGP-
16878 on an adapted growth medium. In a second stage,
doughcomposedof?our,waterandsucroseisstartedwith
the strain LMGP-16878 and fermented at 251C. The
optimum sucrose concentration and fermentation process
parameters were determined. During fermentation, the pH
drops naturallythroughthe organicacid productionofthe
strain, passing all pH levels of enzyme induction, biocon-
version and fermentation of residual fructose (Lazic et al.,
1993; Tsuchiya et al., 1952). The increase of dough
viscosity during this step demonstrates the production of
dextran. The ?nal wheat sourdough is characterized by a
pHcomprisedbetween3.5and3.9,anacidityaround40ml
of NaOH
0,1N
/10g, and a viscosity between 4000 and
5500cp. The rye sourdough has a pH between 3.2 and
3.6 and an acidity around 49ml of NaOH
0.1N
/10g. These
sourdoughs are used at a level of 10% on ?our weight and
improve volume and texture of the baked products.
5. Applications of dextran in bakery
The advantages of this speci?c type of dextran and the
dextran containing sourdoughs in bakery applications are
multiple. More water can be bound in the dough: as
dextran is a hydrocolloid, it can bind high amounts of
water. Higher dough yield often leads to an improved
freshness of the end product. Dextran improves dough
stability and gas retention through a structure build up of
thedextransandinteractionwithglutennetwork.InFig.3,
itisclearlyshownthatdextransbuildupacertainstructure
when a shear force is applied on a1% solution. This is not
the case with the well-known gums like guar and xanthan.
This is probably explained by the fact that the long linear
dextran molecules line up very well and hydrogen interac-
tions occur. The oven jump is signi?cantly better after
addition of dextran. This can also be explained due to the
improved dough stability and gas retention. The crumb
structure is altered. Thegas bubbles are more long shaped,
typical for long fermentation processes. Mouthfeel is
improved: a moister mouthfeel is obtained by addition of
dextran.
The effect becomes even clearer the longer the bread is
conserved. In a lot of applications, a very short bite can
also be experienced after addition of a dextran containing
sourdough. The softness of the bread crumb is measured
ARTICLE IN PRESS
Table 1
Effectof additionof dextransproducedby different strainson ?nalbread
volume and comparison with guar gum (European patent EP 0 790 003
B1)
Volume increase compared
to reference (vol%)
Reference+0.5% guar 10
Reference+1% guar 5
Reference+0.5% dextrans B512F 8
Reference+1% dextrans B512F 12
Reference+0.5% dextrans LMGP-
16878
18
Reference+1% dextrans LMGP-16878 32
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
2 9 7 4 1114161921232628
time (minutes)
viscosity (Pa.s)
guar
xanthan
dextran
Fig. 3. Improved dough stability due to structure build up of dextran.
G. Lacaze et al. / Food Microbiology 24 (2007) 155–160 157
with a texture analyzer. All of these advantages are
described in the patent EP0790003B1 (Vandamme et al.,
1997). The application ?elds of dextran containing
sourdoughs are multiple: from rich wheat doughs (fat,
sugar) up to very heavy rye dough systems (rye breads).
In viennoiserie, the effect of addition of sourdough has
been evaluated in industrial trials (milk bread application).
Reference milk bread (without sourdough) has been
compared with a milk bread containing 5% of a liquid
active wheat sourdough based on dextran. After 2 weeks
conservation, hardness, pH and water activity have been
measured. It has been shown that hardness was signi?-
cantly reduced with liquid wheat dextran sourdough
(Fig. 4). pH of milk bread crumb was reduced by 0.3 units
with the addition of sourdough. Water activity was
identical. A panel test run on 40 people showed that the
milk bread that contained dextran sourdough was sig-
ni?cantlypreferredtothereference.Moreover,aconsumer
panel test hasbeen run on 205 persons in Nantes(France).
Those people were chosen at the exit of a supermarket but
no selection was done on people (age, profession, etc.).
Butter brioches containing wheat dextran sourdough were
compared with brioches without, in a preference tests.
People were asked to rank the product in terms of general
preference,bygivingascorefrom1to10.Thesumofrank
is calculated at the number of people multiplied by the
ARTICLE IN PRESS
0 
100 
200 
300 
400 
500 
600 
700 
800 
Hardness (g)
Essais 747 569
REFERENCE  WITHOUT  SOURDOUGH 5% LIQUID WHEAT SOURDOUGH BASED ON DEXTRAN
Fig. 4. Effect of liquid dextran wheat sourdough on hardness of milk bread after 2 weeks conservation.
460
470
480
490
500
510
520
530
540
550
Sum of ranking
Sum of ranking 492 546
Butter brioche Butter brioche with 5% dextran sourdough
Fig. 5. Effect of dextran sourdough addition in butter brioches on consumers’ preferences.
G. Lacaze et al. / Food Microbiology 24 (2007) 155–160 158
score they gave. It appeared that the brioches containing
dextran sourdough were signi?cantly preferred to the
reference as shown in Fig. 5.
In rye mixed bread, the in?uence of the addition of
dextranryesourdoughontheagingofryemixedbreadwas
evaluated.Softnessmeasurementsweredonewithatexture
analyzer. The softer the bread, the less force the machine
needs to put on the crumb to cause a determined
deformation of the crumb. In parallel, evaluation of
freshness was done by tasting the bread. The results in
the mixed rye bread are shown in Fig. 6 and are expressed
as decrease in hardness of the bread containing dextran.
Softnessandmoistnessofthecrumbofbakedproductshas
been improved both after 4 and 7 days. More remarkably,
the difference between 4 and 7 days is lower when using
dextran sourdough, which shows that also staling of the
crumb is delayed. In these breads, volume and speci?c
volume (volume divided by weight) were also measured.
Bread volume is measured in a typical bakery apparatus
?lled with sesame seeds. Bread volume is deduced from a
ARTICLE IN PRESS
0
500
1000
1500
2000
2500
Hardness (g)
Liquid sorudough 1933 2372
L iquid sourdough based on dextran 1291 1484
Hardness after 4 days Hardness after 7 days
Fig. 6. Hardness measurement in rye breads containing liquid sourdough or liquid sourdough based on dextran.
1.6
1.8
2
2.2
2.4
2.6
2.8
3
3.2
Specific volume
Series1 2.53 2.85 3.02
Liquid rye sourdough
Liquid rye sourdough based on dextran
Liquid rye sourdough based on dextran + Rye 
bread mixe
+ 12 %
+ 25 %
Fig. 7. Effect on dextran sourdough and bread mix on speci?c volume increase in rye breads.
G. Lacaze et al. / Food Microbiology 24 (2007) 155–160 159
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