Solution Properties and Composition of Dextrins - ACS Publications

Chapter 17

Solution Properties and Composition of Dextrins 1

Downloaded by NORTH CAROLINA STATE UNIV on August 2, 2012 | http://pubs.acs.org Publication Date: April 30, 1991 | doi: 10.1021/bk-1991-0458.ch017

Gordon G. Birch, M. Nasir Azudin , and John M. Grigor Department of Food Science and Technology, University of Reading, Whiteknights, P.O. Box 226, Reading, Berkshire RG6 2AP, United Kingdom

Solution properties of dextrins, such as NMR, apparent specific volume and intrinsic viscosity, are similar to those of their components, glucose maltose and higher saccharides. However, fine differences between the individual components of glucose syrups can be precisely monitored by modern solution chemistry techniques and usefully employed to elucidate their mode of interaction with water structure and to predict their behaviour in food systems. Examples are the determination of DE by high resolution NMR and "equivalent DE" (in hydrogenated glucose syrups) by combined measurement of refractometric solids and osmotic pressure, without, recourse to volumetric chemical methods. Solution measurements of glucose syrups or dextrins derived from glucose syrups are based on average molecular weight. In a DE17 glucose syrup, for example, the average apparent specific volume of the dextrin increases from 0.620.63 cm /g as the concentration increases from 5-50% w/w. These figures are high compared to glucose (0.615cm /g) and maltose (0.612cm /g) but low compared to β-cyclodextrin (0.668cm /g). H pmr pulse relaxation analysis of the 17 DE dextrin i n concentrated solution (65% w/w) allows ring protons, hydroxyl protons and water to be distinguished, and i n this regard the dextrin behaves similarly to sucrose. Thus solution properties provide a useful insight of solute-water interaction. 3

3

3

3

1

1

Current address: Faculty of Food Science and Biotechnology, University Pertanian Malaysia, Serdang 43400 UPM, Selangor, Malaysia

0097-6156/91/0458-0261$06.00/0 © 1991 American Chemical Society

In Biotechnology of Amylodextrin Oligosaccharides; Friedman, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

262

BIOTECHNOLOGY OF AMYLODEXTRIN OUGOSACCHARIDES


Some solution properties of carbohydrates in homologous series (eg. densities) appear to be similar among the members of that series, whereas others (eg. specific rotations) vary markedly and systematically with degree of polymerisation. It i s recognised (1,2) that water stabilises the pyranose ring which, along with the helical order of the amylodextin, contributes to the value of the observed specific rotation [α] D. Thus, a plot of [α] D against DP, for the lowest members of the linear maltodextrin series (Table 1), gives a curve which approaches a limiting value of [α] D of about +200. Table 1 S p e c i f i c R o t a t i o n s and DP f o r l o w e s t members o f t h e l i n e a r m a l t o d e x t r i n s e r i e s (3) DP

Γβ{1

1 2 3 4 5 6 7

D

1

5

(

H2 0 )

+52.6 +136.0 +160.0 +177.0 +180.3 +184.7 +186.4

Computations from t y p i c a l g l u c o s e s y r u p c o m p o s i t i o n s would p r e d i c t s i m i l a r r e s u l t s f o r d e x t r o s e e q u i v a l e n t (DE) a g a i n s t le^lot a s a c t u a l l y observed. Such f i n d i n g s i l l u s t r a t e t h e i n s i g n i f i c a n t c o n t r i b u t i o n s t o f ο(] o f s u c c e s s i v e c o i l s i n t h e amylose h e l i x ; p o l a r i m e t r i c measurements a r e always made a t low c o n c e n t r a t i o n o f s o l u t e t o a v o i d d i s t o r t i o n s due t o s o l u t e - s o l u t e i n t e r a c t i o n . P o l a r i m e t r y has been t r a d i t i o n a l l y used by c a r b o h y d r a t e c h e m i s t s f o r i d e n t i f i c a t i o n and d e t e r m i n a t i o n o f sugar m o l e c u l e s and i s a s e n s i t i v e tool f o r f o l l o w i n g the k i n e t i c course o f h y d r o l y s i s (4). I t has t h e advantage o f p r o v i d i n g a p r o p e r t y o f a s m a l l amount o f s o l u t e i n a l a r g e amount o f s o l v e n t ( w a t e r ) , b u t t h e d i s a d v a n t a g e o f n o t i d e n t i f y i n g t h e r o l e o f water i t s e l f makes p o l a r i m e t r y l e s s a t t r a c t i v e t o t h e c h e m i s t than s p e c t r o m e t r y i n s t u d y i n g s o l u t i o n p r o p e r t i e s o f d e x t r i n s and r e l a t e d s u b s t a n c e s . η

Determination

o f DK by High Resolution Nuclear Magnetic Resonance

(NMK) High r e s o l u t i o n NMR a l l o w s i n d i v i d u a l p r o t o n s o f t h e g l u c o s e m o i e t y i n g l u c o s e s y r u p s t o be d i s t i n g u i s h e d . I f t h e NMR spectrum i s o b t a i n e d f i r s t i n D2O a n d second i n D2O/D2SO4 s o l u t i o n t h e o(and /3-anomeric p r o t o n d o u b l e t s (from t h e f r e e r e d u c i n g groups) can be e a s i l y d i s t i n g u i s h e d from the m u l t i p l e t s o f r e m a i n i n g p r o t o n s . The r a t i o o f the a r e a s o f t h e d o u b l e t s to t h e m u l t i p l e t s thus g i v e s a measure o f t h e degree o f h y d r o l y s i s and DE ( 5 ) .


17.

BIRCH ET AL.

Solution Properties and Composition of Dextrins

T a b l e 11 summarises some approach.

typical

successes

with

this

Table 11 - DE of Glucose Syrups by NMR


DE by Lane & Eynon Titration

21.0 31.0 40.0 50.0 65.0

ί ί

DE by NMR

I ! ! I ;

21.5 29.0 38.5 50.0 66.5

type o f

(5)

O b v i o u s l y t h e t i m e - s a v i n g o f a n i n s t r u m e n t a l t e c h n i q u e o v e r a wet c h e m i c a l method i s o f i n t e r e s t f o r i n d u s t r i a l c o n t r o l b u t D2O solution i s n e c e s s a r y t o a v o i d o v e r l a p p i n g problems from OH signals. Determination of DE by Refractive Index/Osmotic Pressure An o b v i o u s method f o r d e t e r m i n i n g DE r a p i d l y i s t o u t i l i z e a c o l l i g a t i v e p r o p e r t y such a s o s m o t i c p r e s s u r e . As DE o f a g l u c o s e s y r u p i n c r e a s e s s o does t h e t o t a l number o f m o l e c u l e s . C r y o s c o p i c d e t e r m i n a t i o n o f o s m o t i c p r e s s u r e , combined w i t h t o t a l solids d e t e r m i n a t i o n w i t h a r e f r a c t o m e t e r , s u f f i c e t o d e t e r m i n e DE (6) w i t h i n a t o t a l time o f about 3 minutes. Nowadays hydrogenated g l u c o s e s y r u p s c o n s t i t u t e i m p o r t a n t d e x t r i n d e r i v a t i v e s used f o r m a n u f a c t u r i n g p r o d u c t s w i t h s p e c i a l i s e d technological and b i o l o g i c a l properties. Since hydrogenated g l u c o s e s y r u p s b y d e f i n i t i o n p o s s e s s no DE, i t i s i m p o r t a n t t o be a b l e t o a s s e s s t h e i r " e q u i v a l e n t DE", o r i n o t h e r words t h e t y p e of p a r e n t s y r u p from which t h e y were d e r i v e d . The above method, u t i l i s i n g o n l y r e f r a c t o m e t r y and c r y o s c o p y p r o v i d e s a n e x c e l l e n t c o m b i n a t i o n o f s o l u t i o n p r o p e r t i e s t o a c h i e v e t h a t end. Precision Densitometry and Apparent S p e c i f i c Volume A l t h o u g h d e x t r i n s resemble a l l c a r b o h y d r a t e s i n t h e i r similar s o l u t i o n d e n s i t i e s , t h e r e i s good r e a s o n t o suppose that d i f f e r e n c e s i n s t r u c t u r e s h o u l d cause f i n e d i f f e r e n c e s i n s o l u t i o n p a c k i n g c h a r a c t e r i s t i c s o f s o l u t e s and hence d e n s i t y d i f f e r e n c e s . Modem p r e c i s i o n d e n s i t o m e t r y a l l o w s measurements o f d e n s i t y y i e l d i n g s i x s i g n i f i c a n t f i g u r e s and t h u s r e v e a l s f i n e d i f f e r e n c e s between s u g a r s p o s s e s s i n g d i f f e r e n t arrangements o f a x i a l a n d e q u a t o r i a l h y d r o x y l groups. E q u a t o r i a l h y d r o x y l groups a r e more e a s i l y h y d r a t e d t h a n a x i a l and t h e r e s u l t i n g h y d r a t e d s t r u c t u r e i s b e t t e r a b l e t o ' f i t * w i t h s u r r o u n d i n g b u l k water s t r u c t u r e .


263

264

BIOTECHNOLOGY OF AMYLODEXTRIN OUGOSACCHARIDES

The ' f i t ' o f a so Lute w i t h s u r r o u n d n i g water s t r u c t u r e i s o r o b a b l v a prime d e t e r m i n a n t oi* a p p a r e n t molar volume ( V ) which i s c a l c u l a t e d from so L u t i o n d e n s i t y u s i n g t h e e x p r e s s i o n :

_Vn\

I'l

a p p a r e n t molar volume l - mol. wt {s

} w


2

where s where where Wi where to

2

= = = =

d e n s i t y o f sample d e n s i t y o f water a t 20°C mass f r a c t i o n o f water mass f r a c t i o n o f s o l u t e

Apparent M o l a r volume (V) i n c r e a s e s a c c o r d i n g l y w i t h MVvt so a more u s e f u l measure o f degree o f ' f i t w i t h water s t r u c t u r e i s Apparent S p e c i f i c Volume (Y/M\vt) which a l l o w s d i r e c t comparison o f d i f f e r e n t m o l e c u l a r a r c h i t e c t u r e s on a weight b a s i s . The apparent s p e c i f i c volumes o f a l l s i m p l e s u g a r s l i e w i t h i n t h e range 0.680.62 cm g- and r e m a r k a b l y good agreement o c c u r s between analogues w i t h c o r r e s p o n d i n g a x i a l arid e q u a t o r i a l arrangements o f hydroxy 1 groups. Among t h e a l d o p v r a n o s e p a i r s D- g 1 ucose:D-xy.)ose, Dgalactose:!,- a r a b i n o s e and D - f r u o t o s e : D - a r a b i n o s e , f o r example, t h e r a t i o s o f a p p a r e n t s p e c i f i c volumes o f hexose t o pentose i s alwavs 1.2 i n accordance w i t h m o l e c u l a r w e i g h t (/). 1

3

1

Apparent molar volumes o f s o l u t e s r e s u l t from t h e p o s i t i v e d i s p l a c e m e n t o f water m o l e c u l e s (depending on m o l e c u l a r s i z e and shape) and the n e g a t i v e électrostriction e f f e c t caused by t h e h y d r a t i o n o f s u i t a b l y d i s p o s e d h y d r o x y ! groups ( 8 ) . F o r t h i s reason h e a v i l y h y d r a t e d structures, such as sugars and o l i g o s a c c h a r i d e s , have much s m a l l e r a p p a r e n t s p e c i f i c volumes than p o o r l y h y d r a t e d s t r u c t u r e s , such a s benzene o r t e t r a h y d r o p y r a n .

Moreover, t h e hydroxy1 s u b s t i t u e n t s a t d i f f e r e n t p o s i t i o n s around the s u g a r r i n g c o n t r i b u t e d i f f e r e n t l y t o t h e o v e r a l l apparent s p e c i f i c volume ( 7 ) . I n gluoopvranose t y p e s o f s t r u c t u r e , a s found i n t h e d e x t r i n s , i t i s t h e 3,4 e ( - g l v o o l system which f u l f i l l s t h i s r o l e , i n d i c a t i n g t h a t t h i s i s t h e mosty h e a v i l y h y d r a t e d r e g i o n o f the m o l e c u l e . I t i s a l s o s i g n i f i c a n t t h a t t h e 3 , 4 o ( - g l y c o l system appears t o be r e s p o n s i b l e f o r sweetness ( 9 ) . T h i s i s whv t h e sweetness o f m a l t o - o l i g o s a o c h a n d e s d e c r e a s e s w i t h i n c r e a s i n g DP (10). The 3,4

Solution Properties and Composition of Dextrins - ACS Publications

Recommend Documents