Industrial Potential of Fungal and Bacterial Polysaccharides - ACS

13

I n d u s t r i a l P o t e n t i a l of F u n g a l a n d B a c t e r i a l Polysaccharides

I. W. COTTRELL

Downloaded by MONASH UNIV on December 4, 2014 | http://pubs.acs.org Publication Date: June 10, 1980 | doi: 10.1021/bk-1980-0126.ch013

Kelco Division of Merck & Co., Inc., 8225 Aero Dr., San Diego, CA 92123

Polysaccharides, or gums as they are known i n industry, have utility because they thicken, suspend, or stabilize aqueous systems. Some gums produce gels, or act as emulsifiers, flocculants, binders, film-formers, lubricants, and f r i c t i o n reducers. Traditionally, these gums have been derived from algal and botanical sources, but more recently, some gums have been derived from microbial sources. These gums are shown i n Table I. Table I. Gums Derived From Algal, Botanical, and Microbial Sources Algal

Botanical

Microbial

agar

guar gum

dextran

algin

gum

arabic

xanthan gum

carrageenan

gum

ghatti

furcellaran

gum

tragacanth

karaya gum l o c u s t bean gum pectin The major o b j e c t i v e o f t h i s article is t o d e s c r i b e the d i v e r s i t y o f p r o p e r t i e s a s s o c i a t e d with p o l y s a c c h a r i d e s d e r i v e d from m i c r o b i a l , i.e., fungal and b a c t e r i a l sources. A l s o I will provide d e t a i l s o f some o f the new b a c t e r i a l p o l y s a c c h a r i d e s o r i g i n a t i n g from our l a b o r a t o r i e s . I will p l a c e emphasis on the key p r o p e r t y or p r o p e r t i e s o f each p o l y s a c c h a r i d e t h a t I d i s c u s s . I will not d i s c u s s p r o p e r t i e s which are not r e l a t e d t o the potential utility of the p o l y s a c c h a r i d e s . I have a l s o d e l i b e r a t e l y omitted d i s c u s s i o n o f the economic aspects o f these polysaccharides. For the p a s t t h i r t y t o f o r t y years, c o n s i d e r a b l e research has been devoted t o the study o f p o l y s a c c h a r i d e s produced by

0-8412-0555-8/80/47-126-251$05.00/0 © 1980 American Chemical Society

In Fungal Polysaccharides; Sandford, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

252

FUNGAL

POLYSACCHARIDES

Table I I . Polysaccharides Produced by Fungi

Polysaccharide Pu1lulan

Organism Aureobasidium

(Pullularia)


Sclerotium

1, ^ - D - g l u c o s e 0C

l 6 -D-glucose

- pullulans Scleroglucan

Structure/ Composition

f

glucanicum

1,3β-D-glucose l,6|3-D-g lucose

Table I I I . Polysaccharides Produced by B a c t e r i a Polysaccharide

Organism

Xanthan gum

Xanthomonas

Curdlan

Alcaligenes faecalis var. myxogenes

Dextran

campestris

Leuconostoc species

Structure/ Composition D-glucose, D-mannose, D-glucuronic a c i d 1,3 β-D-glucose l ^ ^ - D - g l u c o s e 1,2; 1,3; 1,4 -D-glucose Œ

PS-7 Gum

Beijerinckia indica var. myxogenes

glucose (73%), rhamnose (16%), g l u c u r o n i c a c i d (11%)

PS-10 Gum

Soil

bacterium

glucose (39%), g a l a c t o s e (29%), fucose (13%), g l u c u r o n i c a c i d (19%)

PS-21 Gum

Soil

bacterium

mannose (33%), glucose (29%) , galactose (21%), g l u c u r o n i c a c i d (17%)

PS-53 Gum

Soil

bacterium

glucose (41%), fucose (40%), g l u c u r o n i c a c i d (19%)

PS-60 Gum

Pseudomonas species

glucose (41%), rhamnose (30%), u r o n i c a c i d (29%)


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microorganisms i n order to determine t h e i r i n d u s t r i a l potent i a l . (1) During t h i s p e r i o d , s e v e r a l microorganisms have been shown to produce p o l y s a c c h a r i d e s which have i n t e r e s t i n g propersties. These p o l y s a c c h a r i d e s are l i s t e d i n Tables I I and I I I . These tables provide a summary of the major p o l y s a c c h a r i d e s produced by microorganisms which e i t h e r have the p o t e n t i a l , based on t h e i r p r o p e r t i e s , to become commercial products or which have already become products of commerce.


Pullulan

(2)

P u l l u l a n i s the e x t r a c e l l u l a r p o l y s a c c h a r i d e produced by Aureobasidium p u l l u l a n s . The p o l y s a c c h a r i d e i s composed of maltot e t r a o s e u n i t s l i n k e d together through the 1 and 6 p o s i t i o n s on adjacent t r i o s e or t e t r a o s e u n i t s . P u r i f i e d p u l l u l a n i s a white, non-hygroscopic powder which d i s s o l v e s i n hot or c o l d water. P u l l u l a n does not provide high v i s c o s i t y s o l u t i o n s a t low c o n c e n t r a t i o n . The most important property of p u l l u l a n i s the a b i l i t y to form f i l m s . The f i l m s are prepared by d i s s o l v i n g p u l l u l a n i n water at 5-10% c o n c e n t r a t i o n and c o n t i n u a l l y drying the s o l u t i o n a p p l i e d to a smooth s u r f a c e . The major advantage of p u l l u l a n f i l m s i s the very low oxygen permeability. The oxygen p e r m e a b i l i t y of p u l l u l a n f i l m s and three f i l m s of commerce are shown i n Table IV. (3) Table IV. Oxygen Permeability

of P u l l u l a n Films Oxygen Permeability (cc/m , 24 h, atm., 25°C) 2

Sample Pullulan films Cellophane

0.60

-

2.50

4.70

Cellophane (moisture proof)

8.58

Polypropylene

1100

P u l l u l a n f i l m s have s e v e r a l other advantages. The f i l m s are c o l o r l e s s , t a s t e l e s s , odorless, transparent, r e s i s t a n t to o i l and grease, and heat s e a l a b l e . The p r o p e r t i e s of the f i l m s can be modified by chemical m o d i f i c a t i o n of p u l l u l a n , blending with p o l y v i n y l a l c o h o l , g e l a t i n , or amylose, and by a d d i t i o n of p l a s t i c i z e r s . These p r o p e r t i e s i n d i c a t e that p u l l u l a n can be used as a coating or packaging f o r foods to prevent t h e i r o x i d a t i o n . This i s the only apparent outstanding a p p l i c a t i o n f o r p u l l u l a n . Scleroglucan

(4)

S c l e r o g l u c a n i s a capsular p o l y s a c c h a r i d e produced by species of the genus Sclerotium. The p o l y s a c c h a r i d e produced by Sclerotium glucanicum c o n s i s t s of a l i n e a r chain of glucopyranosyl u n i t s


254

FUNGAL POLYSACCHARIDES

l i n k e d (3-g-(l-*3) with s i n g l e glucopyranosyl u n i t s l i n k e d 3-g-(l->6) t o every t h i r d glucose u n i t of the main chain. P u r i f i e d s c l e r o g l u c a n d i s s o l v e s i n hot or c o l d water t o produce high v i s c o s i t y s o l u t i o n s , whereas the crude i s o l a t e from the fermentation broth produces low v i s c o s i t y s o l u t i o n s . These data are shown i n Table V. Table V. V i s c o s i t y of Crude and P u r i f i e d Scleroglucan


Crude Scleroglucan Viscosity*

(1% cone.)

Viscosity*

(0.5% cone.)

Gum

Content

20 - 80 cP

Purified Scleroglucan 1600

cP

500

cP

— 46 - 50%

* B r o o k f i e l d LVT Viscometer, 60

90%

rpm.

Scleroglucan s o l u t i o n s are pseudoplastic or shear t h i n n i n g . The r e l a t i o n s h i p between the v i s c o s i t y of s o l u t i o n s of crude and p u r i f i e d s c l e r o g l u c a n and shear r a t e i s shown i n Figure 1. Based on these curves, s c l e r o g l u c a n does not have a y i e l d value, although the very high v i s c o s i t y at low shear r a t e i n d i c a t e s that s c l e r o g l u c a n may have suspending p r o p e r t i e s . The v i s c o s i t y of s c l e r o g l u c a n at 0.5% concentration and 2% concentration i s e s s e n t i a l l y constant over the range 10° to 9 0 ° C This r e l a t i o n s h i p i s shown i n Table VI. Table VI. E f f e c t of Temperature on the V i s c o s i t y of Crude Scleroglucan S o l u t i o n s Temp. (°C)

V i s c o s i t y a t 2% Cone.

15

1500

25

1400

40

1400

V i s c o s i t y at 0.5% 160

60

1400

80

1400

— — — —

90

1400

140

B r o o k f i e l d LVT Viscometer, 30

Cone.

rpm

The v i s c o s i t y of s o l u t i o n s of s c l e r o g l u c a n i s not changed by changes i n pH over the range 1 to 11. Prehydrated s c l e r o g l u c a n i s compatible with e l e c t r o l y t e s such as 5% sodium c h l o r i d e , 20% calcium c h l o r i d e , 5% sodium s u l f a t e , and 10% disodium hydrogen


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phosphate. Based on these p r o p e r t i e s , i t has been suggested t h a t s c l e r o g l u c a n has u t i l i t y i n p o r c e l a i n and ceramic g l a z e s , extruded r e f r a c t o r y products, p a i n t s , i n k s , p e s t i c i d e sprays, secondary o i l recovery, d r i l l i n g muds, and as a binder f o r ceramics. Xanthan Gum {S_


r

Xanthan gum i s the e x t r a c e l l u l a r p o l y s a c c h a r i d e produced by 5C. campestris. The r e p e a t i n g - u n i t s t r u c t u r e o f xanthan gum i s shown i n F i g u r e 2. (9) As shown i n the f i g u r e , each r e p e a t i n g u n i t contains two glucose u n i t s , two mannose u n i t s , and one glucuronic acid u n i t . The main chain i s b u i l t up of β-D-glucose u n i t s l i n k e d through the 1- and 4- p o s i t i o n s ; i . e . , the chemical s t r u c t u r e o f the main chain i s i d e n t i c a l t o that o f c e l l u l o s e . The s i d e c h a i n c o n s i s t s o f a t e r m i n a l (3-D-mannose u n i t g l y c o s i d i c a l l y l i n k e d t o the 4 - p o s i t i o n o f the β-D-glucuronic a c i d u n i t , which i n turn i s g l y c o s i d i c a l l y l i n k e d t o the 2 - p o s i t i o n o f ^-D-mannose. This three-sugar s i d e - c h a i n i s l i n k e d t o the 3 - p o s i t i o n o f every other glucose residue i n the main chain. Also, approximately h a l f o f the terminal D-mannose residues c a r r y a p y r u v i c a c i d k e t a l i c a l l y l i n k e d t o the 4- and 6- p o s i t i o n s . The nonterminal D-mannose u n i t contains an a c e t y l group a t the 6 position. Xanthan gum d i s s o l v e s i n e i t h e r hot o r c o l d water t o produce high v i s c o s i t y s o l u t i o n s a t low c o n c e n t r a t i o n . The r e l a t i o n s h i p between v i s c o s i t y and c o n c e n t r a t i o n i s shown i n F i g u r e 3. Xanthan gum has a v i s c o s i t y o f approximately 300 cP a t a c o n c e n t r a t i o n o f 0.5% and 1400 cP a t a c o n c e n t r a t i o n o f 1.0% when measured a t 60 rpm with a B r o o k f i e l d Model LVF viscometer a t -25C. Xanthan gum s o l u t i o n s have unique r h e o l o g i c a l p r o p e r t i e s . Aqueous s o l u t i o n s o f xanthan gum are h i g h l y p s e u d o p l a s t i c ; that i s , the v i s c o s i t y decreases r a p i d l y as the shear r a t e i s increased. This decrease i s instantaneous and r e v e r s i b l e . This aspect o f the r h e o l o g i c a l p r o p e r t i e s of xanthan gum s o l u t i o n s i s shown i n F i g . 4. The property o f p s e u d o p l a s t i c i t y i s a l s o r e f e r r e d t o as shearthinning. Xanthan gum s o l u t i o n s a l s o have a r h e o l o g i c a l y i e l d p o i n t t h a t i s apparent a t concentrations g r e a t e r than 0.75%. The shear s t r e s s , shear r a t e curve i s shown i n F i g u r e 5. These data were obtained by use o f the Wells-Micro B r o o k f i e l d viscometer and the r e l a x a t i o n technique o f Patton (1966). The working y i e l d p o i n t i s d e f i n e d as the shear s t r e s s a t a shear rate o f 0.01 s e c " . As can be seen from the f i g u r e , a 1.0% xanthan gum s o l u t i o n has a working y i e l d p o i n t o f 50 dynes cm~^, whereas guar has e s s e n t i a l l y no working y i e l d p o i n t . Xanthan gum s o l u t i o n s a r e remarkably r e s i s t a n t t o thermal degradation. Exposure t o temperatures as high as 80°C f o r extended p e r i o d s has l i t t l e e f f e c t on the v i s c o s i t y o f xanthan gum s o l u t i o n s . This r e s i s t a n c e t o thermal degradation i s enhanced by the presence o f 1


256



Figure 2.

Xanthan gum structure


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10K

0.5

1.0 1.5 2.0 2.5 Concentration (%)

0.1

Figure 3. Relationship between viscosity and concentration for xanthan gum with 0.1% NaCl

3.0

1

10 100 1K 10K 100K Shear Rate (sec ) -1

Paint

Paint Brushing

Pouring Mixing

Sagging Suspension Brookfield Haake

•

""

Spraying •

1

Paper Coating

Hercules Zahn cup

Figure 4.

Rehtionship between shear rate and viscosity for xanthan gum



258

10

m


GUAR / GUM/

0.1

. 100

Figure 7. Viscosity of xanthan gum, locust bean gum solutions (

Industrial Potential of Fungal and Bacterial Polysaccharides - ACS

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