Scleroglucan - Food Technology and Biotechnology

S.A. SURVASE et al.: Fermentative Production of Scleroglucan, Food Technol. Biotechnol. 45 (2) 107–118 (2007) 

107 

ISSN 1330-9862 

(FTB-1693) 

review 

Scleroglucan: Fermentative Production, Downstream 

Processing and Applications 

Shrikant A. Survase, Parag S. Saudagar, Ishwar B. Bajaj and Rekha S. Singhal* 

Food Engineering and Technology Department, Institute of Chemical Technology, 

University of Mumbai, Matunga, Mumbai 400 019, India 

Received: April 11, 2006 

Accepted: November 6, 2006 

Summary 

Exopolysaccharides produced by a variety of microorganisms find multifarious industrial 

applications in foods, pharmaceutical and other industries as emulsifiers, stabilizers, 

binders, gelling agents, lubricants, and thickening agents. One such exopolysaccharide is 

scleroglucan, produced by pure culture fermentation from filamentous fungi of genus Sclerotium. 

The review discusses the properties, fermentative production, downstream processing 

and applications of scleroglucan. 

Key words: scleroglucan, exopolysaccharide, Sclerotium glucanicum, Sclerotium rolfsii, fermentation 

Introduction 

Exopolysaccharides produced by a variety of microorganisms 

are chemically well defined and have attracted 

worldwide attention due to their novel and unique 

physical properties. These exopolysaccharides find multifarious 

industrial applications in foods, pharmaceutical 

and other industries as emulsifiers, stabilizers, binders, 

gelling agents, lubricants, and thickening agents. These 

are rapidly emerging as new and industrially important 

source of polymeric materials, which are gradually becoming 

economically competitive. 

Microbial polysaccharides serve different functions 

in the microbial cells and are distinguished into three 

main types: 

1. Intracellular polysaccharides, which provide mechanisms 

for storing carbon or energy for the cell; 

2. Structural polysaccharides, which are components of 

the cell structure or are integral parts of the cell wall; 

3. Extracellular polysaccharides or exopolysaccharides, 

which, depending on the microbial system, (i) form 

capsules outside the cell, thereby becoming a part of 

the cell wall, or (ii) form slimes that accumulate outside 

the cell wall and which subsequently diffuse in 

the liquid phase during the fermentation. 

Microorganisms that produce a large amount of 

slime have the greatest potential for commercialization, 

since these exopolysaccharides can be recovered from 

the fermentation broth. A list of such biopolymers is 

shown in Table 1 (1). One such exopolysaccharide is 

scleroglucan. 

Scleroglucan – producers and world market 

The production of scleroglucan was first reported 

by Halleck (2) who observed Sclerotium glucanicum to 

secrete this extracellular polysaccharide. Pillsbury Co. 

introduced scleroglucan in the market under the trade 

name Polytran ® , and in 1976 it was commercialized by 

CECA S.E. (France) under the name Biopolymer CS ® . 

Subsequently, Satia, a division of Mero-Rousselot (France), 

produced scleroglucan under the trade name of Actigum 

CS6 ® . Sanofi Bio-Industries (Carentan, France), which 

obtained the rights from Satia and CECA, were the main 

scleroglucan producers, trading scleroglucan under the 

commercial names Polytran ® and Actigum ® , respectively 

(3,4). Sanofi Bio-Industries were acquired by Degussa 

*Corresponding author; Phone: ++91 22 24 145 616; Fax: ++91 22 24 145 614; E-mail: rekha@udct.org

108 S.A. SURVASE et al.: Fermentative Production of Scleroglucan, Food Technol. Biotechnol. 45 (2) 107–118 (2007) 

Table 1. Various exopolysaccharides of industrial importance 

Product Substrate Microorganism Yield*/% 

Alginate Sucrose Azotobacter vinelandii NCIB 9068 5 

Curdlan type Glucose 5 % Alcaligenes faecalis var. myxogenes 10C3 IFO 13140 50 

Levan Sucrose 2 % Zymomonas mobilis NCIB 8938


109 

and stable molecular mass under different fermentation 

conditions. When dissolved in water, scleroglucan forms 

linear triple helices (9), where the side glucose groups 

protrude and prevent helices from aggregating. This stabilizes 

the polysaccharide, but reduces its gelling ability. 

The triple helix structure is quite thermostable, but dissolves 

into single random coils when dispersed in dimethyl 

sulphoxide (DMSO) or at pH over 12.5. Scleroglucan 

has a structure that is identical to schizophyllan, which 

is produced by Schizophyllum commune. Schizophyllan has 

slightly higher molecular mass than scleroglucan (10). 

Properties of Scleroglucan 

The properties of scleroglucan may be influenced by 

the molecular mass and by recovery methods. In addition, 

the solution properties of scleroglucan may also be 

different, depending on the grade used. Biopolymer CS-6 

contains 60–70 % of scleroglucan, whereas biopolymer 

CS-11 is a refined product containing 85–90 % polysaccharide. 

Dissolution 

Scleroglucan disperses rather easily in water at room 

temperature due to the presence of b-D-(1–6)-glucopyranosyl 

groups that increase the solubility of the polysaccharide 

and decrease the ability to form the gels (3,11). 

Refined grades of scleroglucan dissolve readily in hot and 

cold water to form pseudoplastic solutions with shear 

thinning characteristics that tolerate high temperature, 

broad range of pH, and a variety of electrolytes, whereas 

the crude isolate from the fermentation broth produces 

low viscosity solutions. Mixing, temperature, pH, and 

concentration influence the rate at which viscosity develops. 

The viscosity of scleroglucan solutions is affected 

only slightly by temperature variations. At 0.5 

and 2.0 %, it remains practically constant between 10 

and 90 °C. At low temperatures, close to 7 °C, solutions 

of scleroglucan form thermoreversible gels that may be 

caused by weakly interacting triple helix cross linking 

mechanism (10). The viscosity of scleroglucan is unaffected 

over a pH range of 1 to 11. In dimethyl sulphoxide, 

in aqueous solutions of pH=12.5 or higher, or at 

temperatures above 90 °C, the reduced viscosity, specific 

rotation, and sedimentation coefficient indicate disruption 

of the triple helical structure to a single random coil 

(12). Among 140 polymers tested for use in polymer 

flooding in the North Sea oil reservoirs, scleroglucan 

was the most stable, retaining more than 90 % of its viscosity 

after 500 days at 90 °C in seawater (5). 

Scleroglucan forms stable gels in the presence of 

chromium salts and borax at pH=10–11, and can be precipitated 

by the addition of quaternary ammonium salts 

under alkaline conditions. 

Compatibility 

Prehydrated scleroglucan is compatible with electrolytes 

such as 5 % sodium chloride, 5 % sodium sulphate, 

20 % calcium chloride, and 10 % disodium hydrogen 

phosphate (11). However, when the electrolyte concentrations 

are very high, solutions may gel and flocculate. 

Scleroglucan is compatible, without synergism, with most 

other thickeners such as locust bean gum, alginates, xanthan, 

and carrageenan and cellulose derivatives. While 

scleroglucan remains soluble in the mixtures containing 

50 % of glycols or polyols, solutions have high viscosity 

only when the polyol concentration is above 20 % (5). 

Rheology 

Pseudoplasticity, or shear thinning, is the salient characteristic 

of scleroglucan solutions. Pseudoplasticity is 

evident in the gum solutions of 0.2 % or lower, but the 

flow becomes progressively more Newtonian as the concentration 

decreases below 0.2 %. Solutions containing 

less than 0.8 % of scleroglucan are not significantly thixotropic, 

except at temperatures dropping to 10 °C and 

below. Above 20 °C, as determined by the Brookfield- 

-type viscometer, the hysteresis loops traced by the response 

of shear stress to increasing and decreasing shear 

rate are of negligible proportions (7). 

Due to high degree of pseudoplasticity, gel states are 

not always clearly defined. Thus, 1.2–1.5 % solutions of 

purified gum form self-supporting sliceable gels at approximately 

25 °C, but at temperatures below 10 °C, 

even very diluted solutions form diffusely structured 

gels that tend to shrink and undergo syneresis when left 

undisturbed for long periods of time. Such diffused gels 

disperse quickly with mild agitation. 

Suspending properties 

A pseudoplastic flow system inherently combines a 

capacity for suspending fine particles with good pourability 

of suspension. Purified scleroglucan at 0.1–0.2 % effectively 

stabilizes 5–10 % aqueous suspensions of fine 

powders such as zinc oxide, reprecipitated calcium carbonate, 

and sulphamerazine. The viscosity of combinations 

of scleroglucan with bentonite suspensions is markedly 

synergistic. Thus, while the apparent viscosities of 

0.15 % purified gum and 5 % bentonite are around 200 

and 300 cps, respectively, a combination of the two yields 

the viscosity of >4000 cps. Although not a primary emulsifier 

in the sense of a surfactant, scleroglucan enables 

very low energy dispersion during the formation of stable 

oil-in-water emulsions. In addition to the suspending 

action of the pseudoplastic system, prevention of coalescence 

seems to underlie this kind of stabilization (3,5). 

Physiology 

Short and long term feeding studies with rats and 

dogs have not shown any toxicity, blood abnormalities, 

or significant tissue pathology. Eye and skin tests involving 

guinea pigs, rabbits and humans have not demonstrated 

significant adverse reactions or sensitization. With 

chicks and dogs, scleroglucan in the diet lowered the 

cholesterol levels and increased the excretion of lipids 

(13). Like other b-glucans, scleroglucan displays antitumor 

activity, but it is more effective than other polysaccharides 

such as curdlan and b-glucan. 

Microbial Strains Producing Scleroglucan 

Scleroglucan is synthesized extracellularly by species 

of the genus Sclerotium, i.e. Sclerotium glucanicum, Sclerotium 

rolfsii and Sclerotium delphinii. Corticium rolfsii and


Schizophyllum commune produce other polysaccharides that 

are structurally very similar to scleroglucan (2,14). The 

two main species for its production are Sclerotium glucanicum 

(15–18) and Sclerotium rolfsii (6,19–23). 

Sclerotium glucanicum and Sclerotium rolfsii are heterotrophic 

filamentous fungi, which are characterized as 

plant pathogens and parasites. They possess enzymes including 

cellulases, phosphatidase, arabinase, exogalactanase, 

polygalacturanase, galactosidase and exomannase. 

These organisms also produce oxalic acid, which facilitates 

plant cell lysis. Sclerotium species have brown or 

black sclerotia (aggregated bodies of hyphae) or light- 

-coloured mycelia, and do not sporulate (24). Sclerotia 

are more resistant to biological or chemical degradation 

than mycelia. In liquid media the organism forms pellets 

with central capsules from which hyphal residues extend. 

On solid media, aerial hyphae are formed and organized 

in mycelia. The role of scleroglucan in the life of 

the organism is mainly to assist in attachment to plant 

surfaces and the protection of sclerotia against unfavourable 

environmental conditions such as desiccation (25). 

In addition, scleroglucan may have a role as energy 

source. The hydrolytic enzymes synthesized by Sclerotium 

species degrade scleroglucan into glucose molecules, 

indicating that the microorganisms may utilize the 

biopolymer when other carbon sources are depleted 

(26). 

Farina et al. (27) measured the colony radial growth 

rate (Kr) on solid medium of colonies of Sclerotium rolfsii 

Proimi F-6656 for the evaluation of scleroglucan production 

medium and other different media, incubation temperature 

and tolerance to diverse concentrations of sucrose 

and NaCl. The optimum growth temperature observed 

was 30 °C. The fungus tolerated concentrations 

of sucrose from 0.15 to 1.17 M on both Czapek and production 

medium. Growth was limited by the highest 

concentrations of sucrose tested (0.88 and 1.17 M), as indicated 

by a slower increase in colony size. Addition of 

0.86 M NaCl to the production medium and yeast extract-malt 

extract agar (YMA) did not inhibit the growth 

completely, but decreased the radial growth rate considerably 

(80 and 70 %, respectively). 

Biosynthetic Pathway 

Sutherland (28,29) suggested a general pathway for 

the biosynthesis of extracellular polysaccharides in three 

major steps: (i) substrate uptake, (ii) intracellular formation 

of polysaccharide, and (iii) extrusion from the cell. 

There is very little information available on the biosynthesis 

for scleroglucan formation in Sclerotium glucanicum 

and Sclerotium rolfsii, but generally this should 

resemble the biosynthetic steps encountered in the production 

of other glucans. First, glucose is transferred 

into the cells via a hexokinase and is then phosphorylated 

by the action of phosphoglucomutase (PGM) and 

phosphoglucoisomerase (PGI). Pyrophosphorylase (UGP) 

catalyses the formation of uridine diphosphate glucose 

(UDP-glucose), which reacts with lipid carrier and initiates 

polymerisation. This proposed pathway for the production 

of scleroglucan is depicted schematically in Fig. 

2(7). 

Fermentative Production of Scleroglucan 

In general, factors affecting scleroglucan production 

include inoculum preparation, growth medium, environmental 

conditions, and the formation of byproducts. 

Increasing the rate and extent of polysaccharide synthesis, 

eliminating undesirable enzyme activities or trans- 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 2. Biosynthetic pathway for scleroglucan synthesis


111 

ferring the genetic determinants of polysaccharide synthesis 

to more amenable host organisms can improve 

the polysaccharide production. 

Effect of composition of culture medium 

The amount of carbon substrate converted by the cell 

to polymer depends upon the composition of growth medium 

and under certain conditions the product may not 

be produced at all. Generally, media containing high 

carbon to limiting nutrient ratio (often nitrogen) is favoured 

for polysaccharide production. Conversion of 

60–80 % of the utilized carbon source into crude polymer 

is commonly found in high yielding polysaccharide 

fermentations. Care must be taken in the interpretation 

of such yields because crude products often contain 

cells, other organic materials and salts which are co-precipitated 

with the polymer when it is recovered from 

fermentation broth (1). 

The optimal design of the medium is very important 

in the growth of microorganisms, stimulating the 

formation of products and providing the necessary energy 

for metabolic purposes. The nutrients required by a 

fungus include macronutrients such as carbon, oxygen, 

nitrogen, phosphorus, sulphur, potassium and magnesium, 

which comprise an average 98 % of dry cell mass 

of fungi. 

Carbon source 

Usually, glucose and sucrose are used as carbon 

sources for biopolymer production, although other carbohydrates 

can also be utilized. Most studies on scleroglucan 

report a glucose or sucrose concentration of either 

30 g/L (18) or35g/L(21). Under these conditions, 

a maximum yield of 8.5–10 g/L was obtained for scleroglucan, 

which is much lower than the highest reported 

concentration of 27 g/L of xanthan, the main rival of 

scleroglucan. Sucrose concentrations above 45 g/L have 

been found to inhibit growth of Sclerotium glucanicum, 

and further limit the scleroglucan production (30). In 

contrast to this, Farina et al. (19) studied the effect of 

high sucrose concentrations on the scleroglucan production 

by S. rolfsii and concluded that an increase in sucrose 

led to a clear improvement in glucan yield. While 

only 7 g/L of scleroglucan were produced with 30 g/L 

of initial sucrose, a threefold increase (21 g/L) of product 

occurred when 150 g/L sucrose were supplied to the 

culture medium. Despite this improvement, residual sucrose 

at the end of fermentation was as high as 100 g/L, 

thus questioning the economic benefits of this strategy. 

Survase et al. (22) reported the maximum production of 

16.5 g/L at a sucrose concentration of 80 g/L. 

Nitrogen source 

Nitrogen comprises 8–14 % of the dry cell mass of 

bacteria and fungi. It is a component of proteins and enzymes, 

and it is necessary in cell metabolism. A wide 

range of inorganic and organic compounds such as inorganic 

salts of NH 4+ and NO 3– , or more complex, natural 

products such as yeast extract, casein hydrolyzate, soya 

hydrolyzate and corn steep liquor can be utilized to satisfy 

the requirement of this element (31). Generally, the 

addition of extra nitrogen favours the biomass concentration, 

but diminishes glucan formation. In the case of 

a glucan such as pullulan, the production of polysaccharide 

is stimulated by depletion of nitrogen source. Similarly, 

high concentrations of nitrogen in the form of 

ammonium sulphate have been reported to reduce the 

scleroglucan production (19). Also, nitrate rather than 

ammonium sulphate give better glucan levels (19,22). 

Ammonium was reported to inhibit the glucan-synthesizing 

enzymes. 

Miscellaneous 

Phosphorus is an important element for secondary 

metabolism, and it also regulates lipid and carbohydrate 

uptake by the cells. Phosphate salts, such as K 2 HPO 4 or 

KH 2 PO 4 , also serve as a pH buffer in the fermentation 

medium (32,33). Farina et al. (19) indicatedanincrease 

of total phosphorus from 0.12 to 0.28 g/L to improve 

scleroglucan production (from 4 to 5 g/L). Although a 

clear explanation for this was not given, it is possible 

that phosphorus might increase glucose uptake and metabolism. 

Potassium is the principal inorganic cation in the 

cell; it is usually added as an inorganic salt (e.g. K 2 SO 4 , 

K 2 HPO 4, or KH 2 PO 4 ). Potassium is a cofactor for some 

enzymes, required in the carbohydrate metabolism and 

in many transport processes. Magnesium is also required 

by fungi, it functions as an enzyme cofactor, and is present 

in cell walls and membranes. It is usually supplied 

as MgSO 4·7H 2 O. 

Pilz et al. (34) noticed that thiamine and zinc addition 

in a defined mineral medium could replace yeast 

extract. Their results indicate the importance of meeting 

the zinc requirement of the microorganisms. S. rolfsii 

needs Zn 2+ for its primary metabolism and for the production 

of scleroglucan in a mineral medium. 

Effect of precursors 

Addition of precursor molecules is of considerable 

importance in the polysaccharide synthesis in terms of 

metabolic driving force. In case of polysaccharides, higher 

intracellular levels of nucleotide phosphate sugars under 

nitrogen-limited conditions enhance metabolite flux 

of exopolysaccharide synthesis. Higher intracellular levels 

of UMP under nitrogen-limited conditions enhance 

metabolite flux of curdlan synthesis in Agrobacterium species 

(35). Gellan precursors were detected by enzyme assays, 

and they were found to be nucleotide phosphate 

sugars (36). Amino acids have been used by some researchers 

as nitrogen source or as stimulator for improving 

biopolymer yields such as gellan gum production (37). 

Although there is inadequate information available on 

the use of amino acids as precursors for scleroglucan production, 

L-threonine was used in the optimized medium, 

but it did not show an increased yield (19). Survase et al. 

(23) used sugar nucleotides and amino acids and concluded 

that sugar nucleotides such as UMP, UDPG and 

amino acid such as L-lysine could serve as metabolic precursors 

for the scleroglucan production. Addition of precursors 

significantly improved the yield, but not the molecular 

mass of scleroglucan.


Effect of environmental factors 

Microorganisms respond rapidly to environmental 

changes in many different ways, such as induction and 

repression of protein synthesis, change in cell morphology, 

and enzyme inhibition or stimulation. In a bioreactor, 

the main environmental parameters of interest are 

pH, temperature, dissolved oxygen, and stirrer speed. 

The physiology of Sclerotium glucanicum has been 

studied by many people in order to understand how the 

microorganism functions and responds to the controlled 

environment, and to optimize process conditions for 

scleroglucan production. 

Temperature 

The internal temperature of the microorganism must 

be equal to that of its environment. Like many chemical 

reactions, the microbial activity is sensitive to environmental 

temperature. Temperature is crucial parameter 

that affects both culture growth and polysaccharide production. 

However, optimal temperature for exopolysaccharide 

production (20–37 °C) (2) isdifferentfromthat 

for culture growth (28 o C) (15). Below 28 °C, oxalic acid 

formation is enhanced, which has an adverse effect on 

scleroglucan production. 

pH 

pH influences the physiology of a microorganism 

significantly by affecting nutrient solubility and uptake, 

enzyme activity, cell membrane morphology, byproduct 

formation and oxidative reductive reactions. Culture pH 

can have profound effects on both the rate of production 

and the synthesis of polysaccharides. As with temperature, 

the appropriate pH for maximum production of the 

polysaccharide can differ from that for optimum growth. 

In case of xanthan production, Moraine and Rogovin (38) 

observed that culture pH influenced polysachharide production 

more than cell growth. Kang and Cottrell (39) 

reported fungal biopolymer synthesis to be optimal in 

the range of pH=4.0–5.5. Based on these observations, 

researchers have developed two-stage processes, with 

the first stage designed for optimal culture growth and 

the second stage for maximum polysaccharide production. 

Lacroix et al. (40) conducted fermentations for pullulan, 

another fungal glucan, wherein at the first stage, 

the pH of 2.0 was maintained for the best biomass and 

growth rate. Once high levels of biomass were achieved, 

the pH was adjusted to 5.5 for maximum pullulan production. 

In a similar mode, Wang and McNeil (16) reported 

an improved scleroglucan production via atwo- 

-stage process. In the first phase, pH was controlled at 

3.5 for optimal growth, after which pH=4.5 was used to 

promote polysaccharide synthesis. The increased production 

of scleroglucan achieved under these conditions 

was combined with a 10 % reduction of byproduct formation. 

This probably indicates that at pH levels higher 

than those for optimal growth (4.5), carbon flux to biopolymer 

synthesis is increased. In some studies, in order 

to simplify the process and reduce the cost, pH was not 

controlled after an initial adjustment, but scleroglucan 

production was comparatively low. To keep an optimum 

pH for the high production of the polysaccharide, it is 

necessary to control the pH during fermentation, especially 

in a view of the fact that S. rolfsii responds 

differently to the changes in a single process variable 

depending on whether cultivation is carried in shake 

flasks or in stirred tank reactors. 

Dissolved oxygen 

Oxygen occupies a key role in the life cycle of aerobic 

microorganisms by inducing or repressing several 

enzyme systems of primary or secondary metabolism 

and enables oxidative reactions for nutrient utilization 

and energy generation. It can also have negative functions 

in cell metabolism such as production of peroxide 

and superoxide radicals. The effect of dissolved oxygen 

on biopolymer production by S. glucanicum and S. rolfsii 

was studied, and it was observed that while a high oxygen 

supply increased the cell growth, it decreased the 

glucan formation. However, in the production of some 

polysaccharides such as pullulan (41) and gellan (42), 

oxygen is both stimulatory and vital to polymer synthesis. 

In contrast, the Sclerotium culture responds to limited 

oxygen supply with limited growth and specific stimulation 

of glucan formation (20,43). This is unexpected 

of an aerobic microorganism, but it is possible that a reduction 

in dissolved oxygen affects the fungal morphology 

and broth rheology, which in turn affects cell 

growth and metabolism. Another reason could be enhanced 

respiration at high dissolved oxygen, thereby 

converting more carbon to carbon dioxide and reducing 

it for scleroglucan production (44). Wang and McNeil (17) 

suggested that the stimulation of glucan synthesis at low 

dissolved oxygen could be due to limited cell growth. 

Under these conditions, more carbon of the substrate 

was utilized for scleroglucan formation. In addition, low 

dissolved oxygen causes a decrease in byproduct production 

repressing the synthetic enzyme glycolate oxidase 

(21), thus favouring the flow of carbon towards glucan 

production. 

Aeration and agitation 

Aeration and agitation determine the availability of 

nutrients and dissolved oxygen to the cultures, and control 

the rate of metabolite release from the cells, including 

biopolymers, byproducts and carbon dioxide. In polysaccharide 

production the fermentation medium becomes 

very viscous and exhibits non-Newtonian (pseudoplastic) 

behaviour. With filamentous fungi, apart from the 

concentration of the biopolymer, biomass may also contribute 

significantly to broth rheology. These phenomena 

restrict mixing in the bioreactor, and change the culture 

morphology. At high rates fungal hyphae may become 

fragmented, reducing the viscosity of the broth. On the 

other hand, the formation of mycelial pellets may occur 

at low agitation rates. 

Vigorous agitation and aeration are usually beneficial 

for polysaccharide production, although contradictory 

reports are also available. McNeil and Kristiansen 

(45) indicated that increased agitation improves glucan 

synthesis by A. pullulans as well as polymer quality 

(high molecular mass), and influences culture morphology 

by promoting the formation of yeast type (instead 

of filamentous) cells, which seems to produce more glucan. 

For S. glucanicum, a higher growth rate was achieved


113 

with increased aeration rate at an agitation level of 600 

rpm, but more glucan was produced as aeration was reduced 

(42). The same authors reported that at high stirring 

rates, mechanical degradation of glucan and cell 

damage may occur; but if the shear rate applied in the 

bioreactor is not adequate, only low molecular mass 

scleroglucan is released from the cells, while larger remain 

attached to the cell surface. Schilling et al. (20) confirmed 

that high stirring rates yield scleroglucan of low 

molecular mass as compared to that obtained after moderate 

agitation. 

oxaloacetate to oxalate and acetate, or the oxidation of 

glyoxalate to oxalate. This pathway of oxalate formation 

is shown in Fig. 3 (51). 

 

 

 

Other factors 

Some operational strategies can influence the production 

of polysaccharides. Rau et al. (43) reported fed- 

-batch cultivation to result in higher rates of glucan formation 

than batch process. Fed-batch cultivation had 

previously been reported by Shin et al. (46) for pullulan 

production, where the addition of part of the carbon 

source at a later stage could improve pullulan formation. 

Taurhesia and McNeil (47) found that in the production 

of scleroglucan by S. glucanicum the addition of 

sugar in the non-growth phase might enhance the polysaccharide 

formation. But, sometimes the single shot addition 

of the supplementary carbon source may risk the 

sudden increase of the broth sugar concentration, causing 

some degree of inhibition. 

The growth of microorganism and the release of the 

metabolites may also be affected by other factors such as 

light, radiation, and hydrostatic pressure. Miller and Lierta 

(48) observed blue or white light to stimulate b-1,3- 

-glucan accumulation in S. rolfsii. 

Byproduct formation 

Oxalic acid is the main byproduct in the scleroglucan 

production. Its production is undesirable. Oxalic acid 

is a common metabolic product of fungi, and its production 

is linked to the culture conditions and nutrient 

source. The amount of oxalic acid varies with the fungal 

isolate, the carbon and nitrogen source, the initial pH, 

and is also influenced by the presence of buffers or 

other chemicals in the growth medium. The most favourable 

conditions for the oxalate formation include 

high carbohydrate concentration and adequate aeration, 

limited supply of inorganic nutrients, and relatively high 

pH (49,50). Maxwell and Bateman (49) proposed the enzyme 

glyoxalate dehydrogenase to be involved in the 

biosynthesis of oxalate by S. rolfsii, and suggested pH of 

external medium to be a major factor determining oxalate 

accumulation. Production of oxalate is also strongly 

affected by culture medium constituents. The addition 

of L-threonine to the medium reduced the level of oxalic 

acid secreted. Oxalate formation also depends on the nature 

of the carbon source that is used in the medium. 

Maxwell and Bateman (49) also found no growth or oxalate 

accumulation to occur when D-gluconate, pyruvate, 

citrate, fumarate, glycolate, glyoxylate, L-aspartate, glycine 

or glycerol was used as sole source of carbon. 

Many researchers reviewed mechanisms of oxalate 

biosynthesis by microorganisms. They concluded that 

oxalate biosynthesis probably occurs by a number of diverse 

pathways such as the hydrolytic cleavage of 

 

 

 

 

Oxalate formation during fermentation presents a 

two-fold difficulty. First, it presents a diversion of carbon 

source away from exopolysaccharide formation; and 

second, there is a need to separate an oxalate from the 

product. Herve (52) investigated methods to decrease 

the oxalate formation, and found that adjusting the initial 

pH and controlling the addition of NH 4 Cl during 

fermentation could reduce oxalic acid formation without 

reducing the yield. Low pH reportedly activates oxalate 

decarboxylase, which breaks down oxalate to formate 

and carbon dioxide. Schilling et al. (21) proposed low pH 

to reduce the synthetic enzymes, and hence recommended 

a pH of 2.0 to minimize carbon losses to byproducts. 

These authors also found oxygen limitation to decrease 

oxalate production, as the synthetic enzyme glycolate 

oxidase is repressed under anaerobic conditions 

and suggested that early low oxygen supply could be 

beneficial for glucan production. 

Downstream Processing of Scleroglucan 

 

 

 

 

Fig. 3. Proposed route of glucose catabolism and oxalate synthesis 

in S. rolfsii (51) 

Optimization of fermentation parameters alone is 

not enough to ensure a high yield of scleroglucan. The 

next crucial step after the completion of successful fermentation 

is the recovery of scleroglucan. The method 

used for recovery of the exopolysaccharide depends on 

characteristics of the producing organisms, the type of 

polysaccharide and desired grade of purity. Crude products 

may be obtained by drying entire fermentation 

broth. Unattached exopolysaccharide may be separated 

from the cells either by differential centrifugation or by 

filtration. Spray or drum drying or addition of water- 

-miscible non-polar solvents such as acetone, ethanol, or 

isopropyl alcohol can precipitate a polymer and accomplish 

the removal of water. Often the addition of electro-


lytes helps in precipitation by neutralizing the charges 

on the polysaccharides. Recovery of solvents is essential 

for the economic reasons. If desired, the precipitate can 

be further purified by dissolving it in water and then 

dewatering, drying and milling (31,53). 

There are three different methods of recovery reported 

in the literature, which are schematically shown 

in Fig 4. Pretreatment of fermentation broth in all the 

three is common. After obtaining the cell-free broth, the 

procedures for recovery differ. The common pretreatment 

scheme is as follows: fermentation broths are neutralized 

with NaOH or HCl, as required, diluted 3- to 

4-fold with distilled water, heated at 80 °C for 30 min, 

homogenized and then centrifuged (10 000 × g, 30min). 

The pellet so obtained is washed with distilled water 

and dried at 105 °C. The supernatant is then used for recovery 

of scleroglucan. 

In the first method, the clear supernatant is cooled 

at 5 °C and precipitated by adding an equivalent volume 

of ethanol (96 %) or isopropanol. This mixture is allowedtostandat5°Cfor8htocomplete 

exopolysaccharide 

precipitation, after which it is recovered with a 

fine sieve and then redissolved in distilled water. This 

crude exopolysaccharide can be purified twice by ethanol 

(96 %) reprecipitation. Finally, the precipitated polymer 

is either dried at 55 °C for 8 h or freeze-dried and 

milled to whitish glucan powder (6). 

In the second method, divalent cations such as calcium, 

magnesium, manganese, iron, copper, cobalt and 

nickel with the water-miscible organic solvent are used. 

Calcium chloride at 0.5–2.0 % is the preferred divalent 

cation. Addition of calcium chloride results in insoluble 

precipitate of calcium oxalate, which is removed by centrifugation 

or filtration. A water miscible organic solvent, 

such as isopropyl alcohol or ethanol is then added 

to the solution at 20–40 %. The precipitate is separated 

by centrifugation or filtration. The polysaccharide can be 

further purified by rehydration and reprecipitation (54). 

In the third method, recovery of glucan is done by 

employing 0.5–2.0 % calcium chloride, and then adjusting 

the solution to an alkaline pH by addition of metal 

hydroxides. Addition of calcium chloride precipitates the 

calcium oxalate, which is subsequently removed by centrifugation 

or filtration. Then the solution is made alkaline 

to about pH of 10–12 by addition of metal hydroxides 

such as sodium hydroxide or potassium hydroxide. 

The precipitated water-soluble polysaccharide is collected 

by centrifugation or filtration. The purity can be 

increased by repeated precipitation and varying the pH 

(54). 

Applications of Scleroglucan 

Oil industry 

The initial application of scleroglucan was in the oil 

recovery, where it showed better stability than xanthan 

over a wide range of temperature and pH (5,55). In oil 

recovery, scleroglucan increases the viscosity, and hence 

the hydraulic pressure of sea water or brine used to 

extract oil. In watered-out reservoirs where sea water 

 

 

 

 

g 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 4. Different recovery methods of scleroglucan from the fermentation broth


115 

pressure is no longer sufficient to recover the oil, the addition 

of scleroglucan can improve the process significantly. 

In addition, scleroglucan (either in the crude 

form of dehydrated fermentation broth, or as clean, precipitated 

polymer) lubricates the drill and controls the 

backpressures created during drilling (56). Scleroglucan 

is very useful as an oil mud thickener and stabilizer; it 

increases the viscosity of very thin oil muds, which cannot 

otherwise be drilled. In comparison with xanthan, 

scleroglucan has several advantages, for example low 

sensitivity to shear stress and temperatures, which 

makes it suitable for drilling fluid applications. The rheology 

of scleroglucan-oil muds remains unchanged between 

20 and 80 °C, and the scleroglucan-based system 

has higher tolerance to field contaminants (57). 

Improved formulations of scleroglucan for the above 

uses have been developed. Zirconium citrate has been 

used as a deflocculant and dispersing agent in scleroglucan–oil 

muds, and was found to improve field performance 

by its thinning properties. It reduced mud dilution 

requirements, and improved the total fluid costs 

by up to 44 %. In addition, scleroglucan exhibited high 

thermostability in drilling fluids when it was associated 

with polyglycols through intermolecular interactions. 

Food industry 

The food industry worldwide uses 70 000 tonnes of 

polysaccharides per year as thickening agents, stabilizers 

and texturizers. As the emerging food products become 

more complex and diverse, the requirement for 

new and versatile additives is stronger. Presently, different 

polysaccharides are used to modify food viscosity 

and texture. Additionally, polysaccharide gums constitute 

non-fat alternatives that may serve as a source of 

soluble dietary fibre with beneficial health effects at quite 

low levels. They are currently obtained from plants 

(starch, cellulose, pectin, guar gum), seaweed and crustaceans 

(alginate, carrageenans, chitosan) or microbial 

sources (xanthan gum) but the exploration for novel 

candidates still continues (58). 

Scleroglucan in food may be used as a thickener, 

gelling or stabilizing agent. However, xanthan has similar 

properties and applications, and at present it dominates 

the market. If the problem of high cost and low 

productivity of scleroglucan could be overcome, then it 

could replace xanthan in many foods such as jams and 

marmalades, soups, confectionery products and water- 

-based gels, frozen foods, dairy products such as yogurt 

or ice-cream, low calorie or non-fat products, or in fabricated/structural 

foods (2,7,59–64). Scleroglucan could be 

especially useful in food manufacturing where a heating 

process is involved, because of thermal stability that it 

exhibits. 

Vinarta et al. (65) investigated the ability of exopolysaccharides 

EPS I (after 48-hour cultivation) and EPS II 

(after 72-hour cultivation), produced by Sclerotium rolfsii 

ATCC 201126, to minimize the liquid separation (syneresis) 

that occurred during refrigeration of cooked starch 

pastes. After comparing different techniques, the extent 

of syneresis was finally estimated by daily measurements 

of the liquid phase length (Dh) separated above the sedimented 

phase throughout the storage at 5 C. The degree 

of syneresis was represented by Dh/h 0 ,whereh 0 stands 

for the initial height of the sample dispersion. Proportions 

varying between 9.90/0.10 and 9.00/1.00 mass ratio 

for2%masspervolumeofcornstarch/EPS aqueous 

blends were evaluated against 2 % mass per volume of 

corn starch (CS) as control. Up to 20 days of refrigeration 

and for the highest tested proportion (9.00/1.00), 

syneresis could be completely inhibited or reduced 91 % 

by EPS II and EPS I. EPS II was thereby selected as the 

optimal syneresis preventive and subsequent analysis of 

its rheological behaviour in distilled water, skimmed 

and whole milk confirmed the ability to increase viscosity 

with a non-Newtonian, pseudoplastic, behaviour. 

Rheology of CS/EPS II blends, when compared to the 

separated CS and EPS II, also evidenced a desirable synergistic 

effect in the aforementioned solvents, as witnessed 

by the increase in viscosity, higher consistency coefficients 

and lower flow behaviour indices. Additionally, 

EPS II was able to prevent syneresis without affecting 

pH, gelling properties, hardness or colour. These results 

revealed that scleroglucan might become a hydrocolloid 

approved in food with prospective use as food stabilizer 

and for prevention of water loss. 

Immunostimulator and antiviral 

Some complex polysaccharides stimulate immunity 

and increase resistance to neoplastic and/or microbial 

disease. These immunotherapeutics are classified as biological 

response modifiers (BRMs), and b-glucans are the 

most significant BRMs among the carbohydrate BRMs (8). 

Scleroglucan is more effective than other exopolysaccharides 

that also have antitumor activity. The antitumor 

activity of the scleroglucan may be via macrophage participation. 

Water-soluble b-glucans enhance both the number 

and function of macrophages. Scleroglucan has the 

effect of increasing macrophage function in vivo. Scleroglucan 

has higher immune stimulatory, antineoplastic, and 

antimicrobial activity than any other b-D-glucans (66). 

High molecular mass and the presence of (1,6)-b-D-glucosyl 

residue appear to be important for the immunostimulatory 

activity. 

Scleroglucan also has antiviral effect. The mode of 

action against the herpes virus (67) and rubella virus 

(68) has been investigated. The binding of the polysaccharide 

on the host cell membrane may prevent or reduce 

the attachment and entry of the virus into the cell. 

This inhibitory effect occurs only at the early stages of 

infection. The key reaction seems to be the binding of 

scleroglucan with glycoproteins of the cell membrane, 

which impedes the interaction between the virus and 

the host cell plasma. Another possible explanation for 

antiviral activity can be that after the virus enters the 

cell, scleroglucan is also internalized in the cell and encapsulates 

the virus, thus inhibiting its activity. However, 

host cell penetration is unlikely for the case of high 

molecular mass polysaccharides such as scleroglucan. 

Pharmaceutical industry 

Pharmaceutical applications include the use in tablet 

coatings, ophthalmic solutions, injectable antibiotic 

suspensions and calamine lotion. Another important use 

of scleroglucan is in the form of carboxylated derivative


for use as a matrix for drug delivery in the form of tablets 

or films. For this purpose, hydrogels obtained by 

the crosslinking reaction between the polycarboxylated 

derivative of scleroglucan and alkane dihalides were 

evaluated for the diffusion experiments and water uptake 

(69). Here scleroglucan offers advantages of controlled 

release as well as compatibility, biodegradability, 

and bioadhesiveness and thermal and chemical stability 

(70). The peculiar physicochemical properties of scleroglucan 

suggested its suitability as a slow release matrix. 

Tablets prepared with the polymer show a remarkable 

swelling process that can slow down the diffusion of molecules 

previously loaded in the system. Furthermore, during 

the hydration process, the formation of a swelled 

layer slows down the penetration of the dissolution medium. 

This layer therefore represents the rate-limiting 

step of water penetration, which is very important for 

the release of model drugs. Coviello et al. (71) reviewed 

the use of scleroglucan and some derivatives in the field 

of pharmaceutics and in particular for the formulation 

of modified release dosage forms. The native scleroglucan 

can be used for the preparation of sustained release 

tablets (72) and ocular formulations; oxidized and crosslinked 

scleroglucan can be used as a matrix for dosage 

forms sensitive to environmental conditions (73); co- 

-crosslinked scleroglucan/gellan can also be used for the 

drug delivery (74). Furthermore, a novel hydrogel obtained 

with this polysaccharide and borate ions is described 

for the controlled drug delivery (75). 

Other applications 

In cosmetic industry, scleroglucan applications may 

be used in the formulations for hair sprays and in various 

skin care preparations such as creams, protective lotions, 

emollients, demulcents and antisoilants (2,76). 

In agriculture, scleroglucan is a useful antisettling 

agent for phytosanitary products; it facilitates the preparation 

of spraying mixtures and particularly improves 

the contact of the droplets sprayed onto leaves. It may 

also be used in pesticides, defoliant sprays and seed 

coatings (5,7). 

Other suggested uses include porcelain and ceramic 

glazes, extruded refractory products, integrated circuit 

chips, water-based paints, printing inks, liquid animal 

feed concentrates, source of gentiobiose, and as a ceramic 

binder (5,7,77). 

Conclusions 

It is now clear that this polymer has received great 

attention from both oil and pharmaceutical industries. 

Continued research has also led to the formulation of 

many variations of the original product, thereby altering 

its properties and extending its applications. From the 

biotechnological and engineering perspective, the production 

process can be further improved by optimizing 

the fermentation conditions and by producing genetically 

engineered, highly productive mutants of S. glucanicum 

and S. rolfsii in order to achieve better yields and 

reduce the cost. 

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FTB 45 (2) 107-118. 

Skleroglukan: proizvodnja fermentacijom, izdvajanje, 

pročišćavanje i primjena 

Sažetak 

Razni mikroorganizmi proizvode egzopolisaharide koji imaju višestruku 

primjenu u proizvodnji hrane, farmaceutskoj industriji i drugim industrijama, kao 

emulgatori, stabilizatori, učvršćivači, te sredstva za geliranje, podmazivanje i 

zgušnjavanje. Jedan takav polisaharid je skleroglukan proizveden fermentacijom s 

pomoću filamentoznih gljiva iz roda Sclerotium. U ovom se revijalnom prikazu 

raspravlja o svojstvima skleroglukana, njegovoj proizvodnji fermentacijom te 

izdvajanju i primjeni.

Scleroglucan - Food Technology and Biotechnology

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