Extracellular Microbial Polysaccharides

3 Xanthan G u m from A c i d W h e y

Downloaded by CORNELL UNIV on August 29, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0045.ch003

MARVIN CHARLES and MOHAMMED K. RADJAI Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015

Xanthan gum (from Xanthomonas campestris NRRL 1459A) has been produced from media containing deproteinized acid-set or culture-set cottage cheese wheys, the lactose contents of which were hydrolyzed to glucose and galactose by means of immobilized lactase. Both glucose and galactose were used almost completely to give gum yields, productivities and final concentrations which were generally as good as, and in some cases better than, those obtained with comparable conventional media.With the exception of an anomalous pH history (the pH increased rather than decreased) when culture-set whey permeate was used, the fermentations followed courses typical of those previously reported. Details of media preparation, fermentation conditions, and experimental results w i l l follow a brief discussion of cottage cheese whey and whey permeate. C o t t a g e Cheese Whey and Whey Permeate A c i d whey i s t h e h i g h BOD waste r e s u l t i n g from t h e manufacture o f c o t t a g e cheese. I t s composition {!) (see T a b l e I) v a r i e s somewhat w i t h t h e c u r d - s e t t i n g p r o c e s s employed (and w i t h m i l k c o m p o s i t i o n , e t c . ) b u t i n g e n e r a l i t c o n t a i n s around 4% t o 5% l a c t o s e , 0.8% t o 1.0% p r o t e i n ( l a c t a l b u m i n ) , and l e s s e r quant i t i e s o f a c i d s , m i n e r a l s , v i t a m i n s , e t c . Most o f t h e a c i d whey produced each y e a r i s r u n t o waste r e s u l t i n g i n c o n s i d e r a b l e c o s t s t o d a i r i e s and communities. Furthermore, such d i s p o s a l r e s u l t s i n y e a r l y l o s s e s o f o v e r 100 m i l l i o n l b s . o f v a l u a b l e and m a r k e t a b l e whey p r o t e i n ( l a c t a l b u m i n ) , which has e x c e l l e n t n u t r i t i o n a l and f u n c t i o n a l p r o p e r t i e s , and o v e r 500 m i l l i o n l b s . of lactose along with l e s s e r but s i g n i f i c a n t 27

Sandford and Laskin; Extracellular Microbial Polysaccharides ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

EXTRACELLULAR

28

MICROBIAL

POLYSACCHARIDES

q u a n t i t i e s o f o r g a n i c a c i d s and v i t a m i n s . Therefore t h e r e i s c o n s i d e r a b l e economic i n c e n t i v e f o r t h e development o f p r o c e s s e s f o r d i r e c t u t i l i z a t i o n o f a c i d whey o r f o r r e c o v e r y and subsequent use o f i n d i v i d u a l a c i d whey components b u t t h e l a t t e r approach appears t o have g r e a t e r p o t e n t i a l i n t h e f o r s e e a b l e f u t u r e .


Table

I.

A c i d Whey C o m p o s i t i o n

L a c t o s e (wt %) P r o t e i n (wt %) Ash (wt %) L a c t i c A c i d (wt %) Glucono-6-Lactone(wt%) C a l c i u m (G/L) Phosphorous (G/L) T o t a l S o l i d s (wt %) PH

Culture Set 4.3-4.4 0.8-1.0 0.7-0.8 0.6-0.8

—

1.2-1.3 0.7-0.8 6.9-7.0 4.3-4.7

(Typical) Acid Set 4.6-4.9 0.9 0.8-0.9

—

0.04 1.3-1.4 1.9-2.1 7.0-7.2 4.1-4.5

Recovery o f l a c t a l b u m i n by t h e proven t e c h n o l o g y o f u l t r a f i l t r a t i o n o f f e r s c o n s i d e r a b l e economic promi s e t h r o u g h o u t most o f t h e c o u n t r y and a l r e a d y has been operated commercially. However, an i m p o r t a n t f a c t o r i n f l u e n c i n g t h e economics o f t h e r e c o v e r y i s t h e u l t i mate use o f whey permeate which i s t h e b y - p r o d u c t o f u l t r a f i l t r a t i o n and which c o n t a i n s a l a r g e q u a n t i t y o f l a c t o s e , some low m o l e c u l a r weight p r o t e i n , o r g a n i c a c i d s , m i n e r a l s , v i t a m i n s , and some o t h e r minor comp o n e n t s . We r e q u i r e , t h e n , e c o n o m i c a l uses f o r whey permeate (2) . Many s u g g e s t i o n s have been made f o r d i r e c t u t i l i z a t i o n o f permeate i n c l u d i n g c o n v e r s i o n t o y e a s t a n d / o r a l c o h o l (_3) · F e r m e n t a t i o n t e c h n o l o g i e s f o r b o t h a r e w e l l known and i t seems r e a s o n a b l e t o e x p e c t t h a t t h e r e may be some c a s e s i n which such p r o c e s s e s w i l l be e c o n o m i c a l l y f e a s i b l e a l t h o u g h i t must be r e c o g n i z e d t h a t t h e r e l a t i v e l y low economic v a l u e s o f t h e p r o d u c t s might be a d e t e r r e n t t o i n v e s t m e n t . However, i n t h e absence o f r e c e n t well-documented economic s t u d i e s i t i s d i f f i c u l t t o make a s a t i s f a c t o r y a n a l y s i s p a r t i c u l a r l y i n l i g h t o f t h e p o t e n t i a l , b u t somewhat u n c e r t a i n , l a r g e - s c a l e use o f e t h y l a l c o h o l as a f u e l . A n o t h e r approach i n v o l v e s t h e h y d r o l y s i s o f whey permeate l a c t o s e t o g l u c o s e and g a l a c t o s e by means o f i m m o b i l i z e d l a c t a s e (£,!5,£, 1) . W i d e l y d i s c u s s e d food r e l a t e d a p p l i c a t i o n s o f t h e "sweet permeate" so p r o duced a r e based on t h e d e s i r e t o r e c y c l e whey permeate so as t o e l i m i n a t e d i s p o s a l c o s t s , t o d e c r e a s e sweetener c o s t s , and t o c i r c u m v e n t n u t r i t i o n a l and



3.

CHARLES

A N D

RADjAi

Xanthan Gum from Acid Whey

29

f u n c t i o n a l problems a s s o c i a t e d w i t h l a c t o s e . However, d e s p i t e t h e f a c t t h a t t h e h y d r o l y s i s c a n be performed f o r w e l l under ΙΟΦ/lb o f l a c t o s e (5) , t h e "sweet p e r meate" may s t i l l meet w i t h s t i f f c o m p e t i t i o n from a v a i l a b l e c o r n and h i g h f r u c t o s e s y r u p s s i n c e g a l a c t o s e i s n o t as sweet as g l u c o s e and hence on a pound f o r pound ( s o l i d s ) b a s i s t h e h y d r o l y z a t e i s n o t a s sweet as t h e a l r e a d y a v a i l a b l e s y r u p s . Furthermore, i t appears t h a t d e m i n e r a l i z a t i o n w i l l be r e q u i r e d t o make t h e h y d r o l y z a t e a c c e p t a b l e as a food i n g r e d i e n t and t h i s w i l l add c o n s i d e r a b l y t o i t s c o s t (15) . These f a c t s , c o u p l e d w i t h t h e d e c l i n e i n sugar p r i c e s have c a s t some doubt on t h e v e r y p r o m i s i n g economic progno s i s which e x i s t e d f o r t h e use o f "sweet permeate" as a f o o d i n g r e d i e n t j u s t a s h o r t time ago (6) . An a l t e r n a t i v e use o f t h e h y d r o l y z a t e i s as a f e r m e n t a t i o n medium. There a r e many organisms which w i l l m e t a b o l i z e b o t h g l u c o s e and g a l a c t o s e (but n o t l a c t o s e ) t o p r o d u c t s c o n s i d e r a b l y more v a l u a b l e than y e a s t o r a l c o h o l and whose n i t r o g e n r e q u i r e m e n t s a r e s a t i s f i e d p a r t i a l l y o r c o m p l e t e l y by t h e low m o l e c u l a r weight permeate p r o t e i n s . T h i s i s p a r t i c u l a r l y t r u e i n c a s e s where p r o d u c t i o n o f l a r g e q u a n t i t i e s o f c e l l mass i s n o t r e q u i r e d o r even p a r t i c u l a r l y d e s i r a b l e (e.g., i n p r o d u c t i o n o f x a n t h a n ) . F u r t h e r m o r e , demin e r a l i z a t i o n o f the hydrolyzate i s g e n e r a l l y not r e quired f o r this application. Thus, i n s o f a r as use as a f e r m e n t a t i o n medium i s c o n c e r n e d , h y d r o l y z e d p e r meate has t h e f o l l o w i n g advantages: • carbohydrate cost competitive with glucose • adequate n i t r o g e n and o t h e r growth f a c t o r s f o r many a p p l i c a t i o n s » u t i l i z e s a h i g h BOD waste stream •enhances economics o f whey p r o t e i n r e c o v e r y . I t s h o u l d a l s o be n o t e d t h a t even i f c o n d e n s a t i o n i s required to f a c i l i t a t e t r a n s p o r t a t i o n , the cost o f h y d r o l y z a t e would s t i l l be c o m p e t i t i v e w i t h commercial dextrose. The m i c r o b i a l p r o d u c t i o n o f xanthan gum i s a p a r t i c u l a r example o f an a l r e a d y s u c c e s s f u l commercial f e r m e n t a t i o n which uses a c o n v e n t i o n a l g l u c o s e - c o n t a i n i n g medium b u t which c a n be conducted as w e l l o r b e t t e r w i t h a h y d r o l y z e d whey permeate medium. The

Fermentation

Process

Medium F o r m u l a t i o n . The medium c a n be produced from e i t h e r c u l t u r e - s e t o r a c i d - s e t c o t t a g e cheese whey by means o f t h e p r o c e s s i l l u s t r a t e d i n F i g u r e 1: (a) Whey i s f i l t e r e d t h r o u g h a h o l l o w - f i b e r


30

EXTRACELLULAR

(b)


(c)

(d)

MICROBIAL POLYSACCHARIDES

u l t r a f i l t e r h a v i n g a m o l e c u l a r weight c u t o f f o f 50,000 (HF 26.5-45 - XM50 c a r t r i d g e , Romicon, I n c . , Woburn, Ma s s . ) . The permeate, which has a pH o f 4.1-4.6, i s hydrolyzed i n a p i l o t - p l a n t f l u i d i z e d - b e d r e a c t o r c o n t a i n i n g A.niger l a c t a s e (Lactase, L.P., W a l l e r s t e i n , C h i c a g o , IL) i m m o b i l i z e d on alumina p a r t i c l e s (£,7). The h y d r o l y z e d permeate Ts then s t e r i l i z e d and supplemented w i t h s t e r i l e K 2 H P O 4 and MgS04«7H20 t o y i e l d a medium whose composit i o n i s given i n Table I I . The pH o f t h e medium i s a d j u s t e d t o 7.0.

Table I I .

H y d r o l y z e d Permeate M e d i u m ^ ( F u l l S t r e n g t h - C u l t u r e Set)

G l u c o s e (wt %) Galactose Lactose K Mg 2

HPO4 S 0 . 7 H 4

2

0

P r o t e i n (Lowry) Whey A c i d pH

2.05 2.05 0.30 0.50 0.01

0.20 0.70 7.0

(a) Medium a l s o c o n t a i n s whey a s h , a c i d s , vitamins, e t c . W h i l e e i t h e r a c i d - s e t o r c u l t u r e - s e t whey may be used, i t i s i m p o r t a n t t o note t h a t t h e two a r e n o t e q u i v a l e n t as w i l l be i l l u s t r a t e d below. In some c a s e s we have used t h e media d e s c r i b e d as i s w h i l e i n o t h e r s t h e y have been d i l u t e d t o a p p r o x i m a t e l y h a l f - s t r e n g t h , F u r t h e r m o r e , we o c c a s i o n a l l y have added s m a l l q u a n t i t i e s o f supplemental n i t r o g e n i n t h e form o f e n z y m i c a l l y - h y d r o l y z e d l a c t a l b u m i n (Edamin, S h e f f i e l d C h e m i c a l , Union, N J ) . T h i s was p r o v e n t o be p a r t i c u l a r l y v a l u a b l e when a c i d - s e t whey was u s e d . Sterilization. H y d r o l y z e d whey permeate i s a complex medium c o n t a i n i n g sugars and low m o l e c u l a r weight p r o t e i n a l o n g w i t h a c i d s and v a r i o u s m i n e r a l s and hence some c a u t i o n i s n e c e s s a r y d u r i n g steam s t e r i l i z a t i o n , p a r t i c u l a r l y when an a u t o c l a v e i s used as i t was i n o u r c a s e . We found t h a t i f t h e permeate was s t e r i l i z e d a t i t s n a t u r a l pH (4.1-4.6) t h e r e was obs e r v a b l e browning b u t t h e r e was almost no l o s s o f n u t r i e n t s and i n h i b i t o r y p r o d u c t s were n o t formed t o any a p p r e c i a b l e e x t e n t . Indeed, medium steam


3.

C H A R L E S A N D RADJAI

Xanthan

Gum

from Acid

Whey

31


s t e r i l i z e d a t t h e n a t u r a l permeate pH behaved a s w e l l as f i l t e r - s t e r i l i z e d medium. On t h e o t h e r hand, steam s t e r i l i z a t i o n a t pH 6.0 o r g r e a t e r r e s u l t e d i n s e v e r e browning, c o n s i d e r a b l e p r e c i p i t a t i o n , l o s s o f n u t r i e n t s , apparent formation o f r e l a t i v e l y high l e v e l s o f i n h i b i t o r y compounds and a g e n e r a l l y i n f e r i o r medium. Fermentation C o n d i t i o n s . Bench-scale fermentat i o n s were conducted i n 7 l i t e r a e r a t e d , n o n - b a f f l e d f e r m e n t o r s equipped w i t h t h r e e p i t c h e d - b l a d e t u r b i n e i m p e l l e r s h a v i n g tank diameter t o i m p e l l e r d i a m e t e r r a t i o s o f 1.8 t o 1.0. We found t h a t t h e use o f m u l t i p l e l a r g e i m p e l l e r s and t h e i n t e n t i o n a l removal o f b a f f l e s r e s u l t e d i n b e t t e r m i x i n g , oxygen t r a n s f e r , and p r o d u c t i v i t y when t h e f e r m e n t a t i o n b r o t h became v i s c o u s , p a r t i c u l a r l y a t xanthan c o n c e n t r a t i o n s g r e a t e r t h a n 1% (8_) . The f e r m e n t o r s were a l s o equipped w i t h a u t o m a t i c foam c o n t r o l l e r s , d i s s o l v e d oxygen m o n i t o r s , and pH c o n t r o l systems which added e i t h e r 4 N KOH o r gaseous N H 3 . The seed c u l t u r e was d e v e l o p e d as suggested by Moraine and h i s coworkers (9,10,11) and a 5% (V/V) seed was used t o i n o c u l a t e t h e main f e r m e n t o r s i n a l l c a s e s . Temperature was always m a i n t a i n e d a t 28°C and pH a t 7.0 e x c e p t when t h e pH remained above 7 as was t y p i c a l l y t h e c a s e when c u l t u r e - s e t whey was used. Analytical G l u c o s e , g a l a c t o s e , and xanthaa c o n c e n t r a t i o n s were measured a t r e g u l a r i n t e r v a l s . G l u c o s e was d e t e r m i n e d by means o f a g l u c o s e - o x i d a s e impregnated membrane and g a l a c t o s e by means o f a g a l a c t o s e - o x i d a s e impregnated membrane. Both were used i n c o n j u n c t i o n w i t h a YSI Model 23A g l u c o s e a n a l y z e r (YSI I n s t r u m e n t s , Y e l l o w S p r i n g s , O h i o ) . The l a c t o s e c o n t e n t o f unhydrol y z e d whey was u s u a l l y d e t e r m i n e d by f i r s t c o m p l e t e l y h y d r o l y z i n g i t w i t h e x c e s s A . n i g e r l a c t a s e ( L a c t a s e LP, W a l l e r s t e i n , C h i c a g o , IL) and t h e n measuring t h e r e s u l t i n g g l u c o s e o r g a l a c t o s e . In some c a s e s t h e g a l a c t o s e o x i d a s e membrane, which responds t o l a c t o s e t o an e x t e n t o f 10-15% o f i t s r e s p o n s e t o g a l a c t o s e , was used t o determine whey permeate l a c t o s e d i r e c t l y . The l a c t o s e c o n c e n t r a t i o n i n whey permeate used f o r f e r m e n t a t i o n s was c a l c u l a t e d from t h e h y d r o l y z a t e g l u c o s e c o n c e n t r a t i o n (which i s e q u a l t o t h e g a l a c t o s e c o n c e n t r a t i o n p r i o r t o i n o c u l a t i o n ) and t h e known i n i t i a l permeate l a c t o s e c o n c e n t r a t i o n . The l a c t o s e c o n c e n t r a t i o n remained e s s e n t i a l l y c o n s t a n t t h r o u g h o u t a l l t h e f e r m e n t a t i o n s performed as i t was n o t


EXTRACELLULAR

32

MICROBIAL

POLYSACCHARIDES

m e t a b o l i z e d by X . c a m p e s t r i s under t h e c o n d i t i o n s employed. Xanthan was d e t e r m i n e d by f i r s t f i l t e r i n g f e r m e n t a t i o n samples t o remove a l l suspended s o l i d s , p r e c i p i t a t i n g the xanthan i n t h e f i l t r a t e by a d d i t i o n o f KC1(2%) and methanol (50-60%) and f i n a l l y d e t e r m i n i n g t h e d r y weight o f t h e p r e c i p i t a t e d gum.


F e r m e n t a t i o n Modes Both b a t c h and r e p e a t e d - b a t c h f e r m e n t a t i o n s were performed. In r e p e a t e d - b a t c h o p e r a t i o n a g i v e n f e r m e n t a t i o n c y c l e was t e r m i n a t e d when t h e g a l a c t o s e conc e n t r a t i o n dropped t o a p p r o x i m a t e l y 0.1% o r when t h e xanthan p r o d u c t i o n r a t e became i m p r a c t i c a l l y low. At t h a t t i m e , a p p r o x i m a t e l y 85-90% o f the fermentor cont e n t s were r e p l a c e d w i t h f r e s h medium and a new c y c l e was i n i t i a t e d . R e s u l t s and D i s c u s s i o n G l u c o s e / G a l a c t o s e Medium. F e r m e n t a t i o n s were c o n d u c t e d u s i n g media based on 50/50 m i x t u r e s o f pure g l u c o s e and g a l a c t o s e t o p r o v i d e b a s e - l i n e d a t a f r e e o f a m b i g u i t i e s t h a t might a r i s e as a r e s u l t o f t h e complex n a t u r e o f whey-based media. The h i s t o r y o f a t y p i c a l f e r m e n t a t i o n i s g i v e n i n F i g u r e 2 and t h e comp o s i t i o n o f t h e medium used i n T a b l e I I I . Table I I I .

G l u c o s e - G a l a c t o s e Medium

G l u c o s e (wt %) Galactose Edamin K2 HP04 Mg S 0 . 7 H 0 pH 4

2

1.3 1.3 0.06 0.50 0.01 7.0

The most i n t e r e s t i n g p o i n t i l l u s t r a t e d by t h e s e r e s u l t s i s t h e s i m u l t a n e o u s use o f b o t h s u g a r s . A l though g a l a c t o s e was used l e s s r a p i d l y t h a n g l u c o s e t h e r e was c l e a r l y no d i a u x i e . Furthermore, both sugars were u t i l i z e d f o r gum p r o d u c t i o n . Otherwise t h e c o u r s e o f the f e r m e n t a t i o n was t y p i c a l o f t h o s e r e p o r t e d by Moraine and h i s coworkers (£, 10/11.) · The f i n a l gum c o n c e n t r a t i o n o f a p p r o x i m a t e l y 2% which r e p r e s e n t e d a 77% y i e l d was a c h i e v e d i n about 50 h o u r s . C u l t u r e Set Whey; B a t c h F e r m e n t a t i o n . The h i s t o r y o f a t y p i c a l b a t c h f e r m e n t a t i o n based on c u l t u r e - s e t


CHARLES

AND

Xanthan

RADJAI

Gum from Acid

Whey

Mgso

4

IME

K HPO 2

4

Reactor

UltraFilter


Raw Whey "

KOH

Permeate

Concentrate S?Sterilize

Fermentor Figure 1.

Medium preparation 8.0 Ck

4J

U

20

30

Time (Hrs) Figure 2. Batch fermentation; glucose-galactose medium


EXTRACELLULAR

34

MICROBIAL

POLYSACCHARIDES


whey permeate medium i s i l l u s t r a t e d i n F i g u r e 3 and t h e c o m p o s i t i o n o f t h e medium used i s g i v e n i n T a b l e I . The most s i g n i f i c a n t p o i n t t o be noted here i s t h a t the pH b e h a v i o r was v e r y d i f f e r e n t from t h a t observed by o t h e r s u s i n g c o n v e n t i o n a l g l u c o s e media o r by o u r s e l v e s when we used t h e g l u c o s e / g a l a c t o s e medium. We w i l l return to this later. The o t h e r p o i n t worth n o t i n g i s t h a t t h e f i n a l gum c o n c e n t r a t i o n o f 3.5% ( i n a p p r o x i m a t e l y 90 hours) r e p r e s e n t s an 85* y i e l d from t h e a s s i m i l a b l e sugars which was c o n s i d e r a b l y g r e a t e r t h a n would have been expected on t h e b a s i s o f p r e v i o u s r e p o r t s . A g a i n , we w i l l r e t u r n t o t h i s l a t e r . A c i d - S e t Whey: B a t c h F e r m e n t a t i o n . Results of a b a t c h f e r m e n t a t i o n u s i n g h a l f s t r e n g t h a c i d - s e t whey medium supplemented w i t h Edamin and h a v i n g t h e compos i t i o n g i v e n i n T a b l e IV a r e p r e s e n t e d i n F i g u r e 4. T a b l e IV.

Hydrolyzed-Permeate/Edamin M e d i u m ^ (Half Strength-Acid Set)

G l u c o s e (wt %) 1.3 Galactose 1.3 Lactose 0.2 Whey P r o t e i n (Lowry) 0.1 Edamin 0.06 K HP0 0.25 Mg S 0 . 7 H 0 0.005 pH 7.0 (a) Medium a l s o c o n t a i n s whey a s h , a c i d s , vitamins, e t c . 2

4

4

2

I n g e n e r a l , t h i s h i s t o r y i s t h e same a s t h a t f o r t h e f e r m e n t a t i o n i n which t h e g l u c o s e / g a l a c t o s e medium was used a l t h o u g h i t d i d p r o c e e d somewhat more r a p i d l y . In p a r t i c u l a r , t h e pH b e h a v i o r was t y p i c a l and t h e y i e l d was w i t h i n t h e range e x p e c t e d . I t should a l s o be noted t h a t media c o n t a i n i n g a c i d s e t whey b u t no Edamin gave somewhat lower y i e l d s and l o n g e r fermentations. The r e a s o n s f o r t h e enhanced gum p r o d u c t i o n and anomalous pH b e h a v i o r o b s e r v e d when c u l t u r e - s e t whey permeate was used a r e n o t c l e a r . A t t h i s time we c a n o n l y s p e c u l a t e t h a t d i f f e r e n c e s i n whey permeate comp o s i t i o n s must be r e s p o n s i b l e the primary d i f f e r e n c e s b e i n g i n t h e c o n c e n t r a t i o n s o f low m o l e c u l a r weight whey p r o t e i n , and i n t h e c o n c e n t r a t i o n s and composit i o n s o f t h e whey a c i d f r a c t i o n s . However, we c a n n o t r u l e o u t o t h e r f a c t o r s such as d i f f e r e n c e s i n v i t a m i n content. f



CHARLES

AND

0

Xanthan

RADJAI

10

Gum from Acid

©

Glucose

• Δ 0

Galactose Xanthan Viscosity

20

30

40

50

60

70

80

Whey

90 100

Time (Hrs) Figure S.

Batch fermentation; full-strength culture-set whey medium


36

EXTRACELLULAR

0

Glucose

•

Galactose

Δ

Xanthan

POLYSACCHARIDES

Viscosity


Ο

MICROBIAL

0

10

20

30

40

50

Time (Hrs) Figure 4.

Batch fermentation; half-strength acid-set whey medium



3.

CHARLES

AND

RADJAI

Xanthan

Gum from Acid

Whey

Time (Hrs)

Figure 5.

Repeated batch fermentation; full-strength culture-set whey medium


37


38

EXTRACELLULAR

MICROBIAL

POLYSACCHARIDES

Repeated-Batch F e r m e n t a t i o n . Results of a threec y c l e repeated batch fermentation with f u l l - s t r e n g t h c u l t u r e - s e t whey medium (no Edamin) a r e i l l u s t r a t e d i n F i g u r e 5. Other t h a n t h e anomalous pH b e h a v i o r and g r e a t e r - t h a n - e x p e c t e d y i e l d s t h e most n o t a b l e f e a t u r e o f t h e s e r e s u l t s i s t h a t t h e r e was l i t t l e change i n f e r m e n t a t i o n h i s t o r y from c y c l e t o c y c l e . However, i t s h o u l d be o b s e r v e d t h a t t h e r e i s a p e r c e p t i b l e i n c r e a s e i n l a g time from one c y c l e t o t h e n e x t . A t t h i s time we c a n n o t say w i t h c e r t a i n t y t h a t t h i s was a c t u a l l y a t r e n d n o r , i f i t was, c a n we p r e d i c t t h e number o f c y c l e s which c o u l d be performed b e f o r e t h e l a g would become p r o h i b i t i v e l y l o n g . However, we s h o u l d note t h a t because o f t h e c o n s t r u c t i o n o f t h e fermentor t h e c u l t u r e r e t a i n e d as t h e seed f o r t h e next c y c l e always came from t h e v e r y bottom o f t h e v e s s e l where m i x i n g and a e r a t i o n were p a r t i c u l a r l y poor d u r i n g t h e l a s t hours o f each c y c l e . T h i s may have been t h e cause o f t h e i n c r e a s e d l a g t i m e s . Conclusion H y d r o l y z e d whey permeate has been shown t o be a s u i t a b l e and c o m p e t i t i v e medium f o r t h e p r o d u c t i o n o f xanthan gum by X . c a m p e s t r i s . I t supports e x c e l l e n t y i e l d s and h i g h f i n a l c o n c e n t r a t i o n s i n b o t h b a t c h and r e p e a t e d b a t c h o p e r a t i o n p a r t i c u l a r l y when modif i e d n o n - b a f f l e d a g i t a t i o n systems employing m u l t i p l e l a r g e p i t c h e d - b l a d e t u r b i n e i m p e l l e r s a r e used.

The a u t h o r s w i s h t o e x p r e s s t h e i r g r a t i t u d e t o t h e P e n n s y l v a n i a S c i e n c e and E n g i n e e r i n g F o u n d a t i o n f o r s u p p o r t i n g t h i s work under PSEF Agreement #273 and t o Romicon, I n c . f o r t h e i r generous g i f t o f u l t r a f i l t r a t i o n c a r t r i d g e s used i n t h i s work.

Literature Cited 1. 2. 3.

Personal communication, Lehigh Valley Dairy, Allentown, PA. Melicouris, N . , paper presented at Enzyme Technology Transfer and Utilization Conference, Lehigh University, Bethlehem, PA, May 27, 1976. Goulet, J., paper presented at the First International Congress on Food and Engineering, Boston, Mass., August 10, 1976.


3.

CHARLES

A N D RADjAI

Xanthan

Gum from Acid Whey


4.

Si

Coughlin, R. W., Charles, Μ., in "Enzyme Engin eering" ed. Oye, Ε. Κ., and Wingard, L . Β., Plenum Press, N.Y., 1974. 5. Pitcher, W. H., in "Immobilized Enzymes for Indus trial Reactors" ed. R. A. Messing, Academic Press, New York (1975). 6. Charles, Μ., Coughlin, R. W., paper presented at NSF/RANN Grantees Conference, University of V i r ginia, Charlottesville, VA, May 19-21, 1976. 7. Charles, Μ., Coughlin, R. W., Allen, B. R., Paruchuri, Ε. Κ., Hasselberger, F. X . , in "Immobilized Biochemicals and Affinity Chromatography", ed. Dunlay, R. Β., Plenum Press, N . Y . , 1974. 8. Charles, Μ., Zmuda, J., paper presented at AIChE Meeting, Nov. 28-Dec. 4, 1976, Chicago, IL. 9. Moraine, R. Α . , Rogovin, P . , Biotech. Bioeng., 8, 511 (1966). 10. Moraine, R. Α . , Rogovin, P . , Biotech. Bioeng., 13, 381 (1971). 11. Moraine, R. Α . , Rogovin, P . , Biotech. Bioeng., 15, 225 (1973).


Extracellular Microbial Polysaccharides

Recommend Documents