STUDY OF NATIVE STARCH HYDRATION : INFLUENCE OF SORPTION HYSTERESIS

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STUDY OF NATIVE STARCH HYDRATION : INFLUENCE OF SORPTION HYSTERESIS

H. Bizot, A. Buleon, N. Riou

To cite this version:

H. Bizot, A. Buleon, N. Riou. STUDY OF NATIVE STARCH HYDRATION : INFLUENCE OF SORPTION HYSTERESIS. Journal de Physique Colloques, 1984, 45 (C7), pp.C7-259-C7-264.

�10.1051/jphyscol:1984730�. �jpa-00224295�

STUDY OF NATIVE STARCH HYDRATION : INFLUENCE OF SORPTION HYSTERESIS

H. B i z o t , A . Buleon and N. Riou

INRA

-

LSCDA, Rue de Za Ge'raudie're, 44072 Narrtes Cedex, France

Resum@ : L 1 @ t u d e de l a s o r p t i o n de l ' a m i d o n de pomme de t e r r e ii l ' e t a t n a t i f g r a n u l a ~ ~ s e n t e des p a r t i c u l a r i t @ s s t r u c t u r a l e s ( e v a l u a t i o n de l a c r i s t a l l i n i t e apparente decel@e par d i f f r a c t i o n X) e t thermodynamique ( i m p o r t a n t phenomene d'hys- t e r e s i s en l'absence de p o r o s i t e ) . Les r e s u l t a t s presentes ne permettent pas en- core une synthsse e x p l i c a t i v e mais l e s e t a t s obtenus en d e s o r p t i o n r e s u l t e n t pro- bablement de faux e q u i l i b r e ii d e r i v e t r e s l e n t e .

A b s t r a c t : Results concerning water s o r p t i o n i n n a t i v e p o t a t o s t a r c h gra- nules a r e presented f o r s t r u c t u r a l p r o p e r t i e s ( e v o l u t i o n o f apparent X-ray crys-.

t a l l i n i t y w i t h water uptake) and f o r thermodynamical data ( l a r g e h y s t e r e s i s phe- nomenon i n the absence o f d e f i n i t e p o r o s i t y ) . A s y n t h e t i c e x p l a n a t i o n i s n o t y e t p o s s i b l e b u t t h e d e s o r p t i o n pseudo e q u i l i b r i a observed a r e probably t r a n s i t o r y s t a t e s d r i f t i n g v e r y s l o w l y .

S t a r c h i s t h e most i m p o r t a n t photosynthetized polysaccharide a f t e r c e l l u - l o s e i n nature. I t i s t h e main reserve substance f o r a l o t o f h i g h e r p l a n t s and anenergysource f o r many organisms, from b a c t e r i a and molds t o the h i g h e r animals and man. S t a r c h i s mainly e x t r a c t e d from maTze and potatoes and used e s s e n t i a l l y f o r food purposes (50 %) o r o t h e r numerous i n d u s t r i a l processings such as

adhesives, coating, f l o c u l a t i n g , chemicals and b u i l d i n g m a t e r i a l s .

S t a r c h granules (20 t o 80

,,

i n diameter) are complex a r c h i t e c t u r e s o f c o n c e n t r i c s h e l l s w i t h r a d i a l o r i e n t a t i o n s and can have very d i f f e r e n t shapes from t h e n e a r l y p e r f e c t sphere (wheat) t o t h e polyhedral granules i n r i c e . They are c o n s t i t u t e d o f two macromolecules, i n t h e case o f potato, t h e l i n e a r p o l y

[1+4] D anhydroglucose (PD

-

400) c a l l e d "amylose" represents about 20 % o f the a r m a t t e r ; the r e s t i s made o f l a r g e branched "amylopectin" molecules (PD 105 t o ₁₀

6

₎ i n which s i d e chains a r e g r a f t e d about every 20 residues by a [1+6] bounds t o form a t r e e l i k e arrangement. L i n e a r segments have a n a t u r a l tendency t o take a he1 i c a l conformation.

With regard t o i t s h y d r a t i o n p r o p e r t i e s , s t a r c h can be considered as a t h e r - mo-hydro p l a s t i c m a t e r i a l (me1 t i n g a t 60°C when s a t u r a t e d by water : g e l a t i n i z a - t i o n ) . Although 30 % appear t o be c r y s t a l l i n e , g i v i n g c l e a r X-ray d i f f r a c t i o n diagrams e s s e n t i a l l y when hydrated, a l l hydroxyls are f u l l y exchangeable as ob- served w i t h NMR. The s a t u r a t i o n (54 % Hz0 d.b.) would correspond t o o n l y 5 water molecules p e r anhydroglucose c y c l e ( 3 f r e e OH group5,if these were a l l f u l l y avai- l a b l e ) w h i l e n i t r o g e n surface area i s o n l y 0,2 m2/g a f t e r d r y i n g . The s o r p t i o n . o f water molecules m o d i f i e s i n t e r h e l i c a l bonds and t h e s t r u c t u r a l f l u c t u a t i o n s are l i k e l y t o be accompanied by s t r a i n accumulation and r e l a x a t i o n . llany reviews have been made on the p h y s i c a l , biochemical and chemical p r o p e r t i e s o f starches, the most r e c e n t are those o f FRENCH,1984, GUILBOT and MERCIER, 1984 and VAN DEN BERG, 1981. This s h o r t paper reviews o u r c o n t r i b u t i o n t o t h e h y d r a t i o n behaviour o f n a t i v e p o t a t o s t a r c h and p a r t i c u l a r l y h y s t e r e s i s (BIZOT and C o l l

. ,

1984).

I

-

CHARACTERISTICS OF SORPTION EQUILIBRIA and i t s i n f l u e n c e on s t r u c t u r a l and v o l umi c p r o p e r t i e s

A f t e r complete d r y i n g a t 130°C f o r 1 H 30 o r by vacuum d r y i n g a t 50°C (MULTON and C o l l . , 1980) the e q u i l i b r a t i o n r e q u i r e s one day t o a week, t h e i n i t i a l

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984730

C7-260 JOURNAL DE PHYSIQUE

Fickian phase i s followed by a r e l a x a t i o n a l lagging p e r i o d . The s o r p t i o n isotherms obtained by p l o t t i n g t h e w a t e r c o n t e n t versus t h e w a t e r a c t i v i t y (aw =

k)

^of

equi 1 ib r a t i o n a r e we1 1 described by t h e Guggenheim-Anderson-De Boer model which is a g e n e r a l i z a t i o n of BET :

with :

Aw Water a c t i v i t y

W Water c o n t e n t on dry b a s i s

Wm Water c o n t e n t corresponding t o s a t u r a t i o n o f a l l primary adsorption s i t e s by one water molecule(formerly c a l l e d Monolayer i n B.E.T. theory)

C Guggenheim's c o n s t a n t : C = c ' exp

(h

^-Hq)/RT

Hq Total h e a t o f s o r p t i o n o f t h e m u l t i l a y e r which d i f f e r s from t h e h e a t of con- densation o f pure water H 1

Hm Total h e a t o f s o r p t i o n o f t h e f i r s t l a y e r on primary s i t e s

k Factor c o r r e c t i n g p r o p e r t i e s of t h e m u l t i l a y e r molecules with r e s p e c t t o t h e bulk l i q u i d ( K = k ' exp (HI

-

^Hq)/RT)

s e e VAN DEN BERG (1981) and BIZOT H. (1983) f o r d e t a i l s .

Adsorption and desorption isotherms f o r p o t a t o s t a r c h a r e presented on t h e f i g u r e 1 with t h e values obtained by a q u a d r a t i c r e g r e s s i o n f o r Wm, K and C and t h e RMS %. This l a t t e r q u a n t i f i e s t h e f i t t i n g q u a l i t y between experimental p o i n t s and

"GAB" model.

J

X H P 0 d . b P O T A M STARCH RESORPTION

'I DESORPTION SCANN1NG:REVERSRL POI^ A W O . I ~ ~

" Aw=0.226 , r.. ^I

.

Guggenheim r e g r e s s i o n c o e f f i c i e n t s

- s m

" Aw=0.438

-

FIGURE 1. DESORPTION-RESORPTION SCAN- NING CURVES AT 25OC

( f : Reversal p o i n t ; AW = T) Pw DES 13.637

0,687 15.972

5.0 RES

'm K C R M S %

9.979 0,729 26.371

3.9

t u r e i s n o t compulsary f o r h y s t e r e s i s t o develop s i n c e i t i s p a r t i a l l y r e t a i n e d even a f t e r g e l a t i n i z a t i o n (BIZOT e t a1

. ^,

1984). The s o r p t i o n c a p a c i t y and h y s t e r e s i s decrease w i t h i n c r e a s i n g temperatures (about 2 % H20 between 15 and 25°C) due t o an e x o t h e r m ~ c excess heat o f s o r p t i o n and a progressive p l a s t i f i c a t i o n .

The desorption i s n o t uniquely d e f i n e d and depends on (i) t h e number o f successive c y c l i n g s ( f i r s t desorption from f r e s h p o t a t o s t a r c h has 1 % h i g h e r water content) ; ( i i ) t h e e q u i l i b r a t i o n mode ( i n t e r v a l i n m u l t i p l e steps o r i n t e - g r a l i n one step which gives lower values) ; ( i i i ) t h e l o c a l f l u c t u a t i o n s which f a v o u r r e l a x a t i o n and l e a d t o a d r i f t toward r e s o r p t i o n . The r e s o r p t i o n appears t o be much more r e p r o d u c i b l e b u t i n t e r m e d i a t e scanning curves depend on t h e r e - v e r s a l water a c t i v i t i e s which i n f l u e n c e s o r p t i o n up t o s a t u r a t i o n .

I 1

-

THERMODYNAMICAL EVALUATIONS

I n order t o compare w i t h d i f f e r e n t i a l i s o s t e r i c heats c a l c u l a t e d by Clausius- Clapeyron f o r m u l a t i o n (LE MAGUER, 1984) ; the i n t e g r a l heats o f s o r p t i o n have been evaluated from c a l o r i m e t r i c w e t t i n g experiments (Figure 2)

FIGURE CO EVOLUTION OF INTEGRAL HEAT OF WETTING WITH WATER CONTENT AND HYSTERESIS

This shows a s l i g h t h y s t e r e s i s on t h e whole range as observed a l s o by VAN DEN BERG (1976). The desorption heats o f w e t t i n g are h i g h e r than i n r e s o r p t i o n , t h i s d i f f e r e n c e may be a t t r i b u t e d t o an endothermic term corresponding t o t h e energy o f s w e l l i n g . An attempt t o q u a n t i f y h y s t e r e s i s i s presented on f i g u r e 3. F o l l o - wing EVERETT'S proposal (1955) t h e work o f compression done by t h e surrounding d u r i n g a closed c y c l e i s i d e n t i f i e d w i t h the i r r e v e r s i b l e entropy production.

I n t e g r a t i n g t h i s expression u s i n g GAB formula on t h e main h y s t e r e s i s loop and graphical i n t e g r a t i o n f o r p a r t i a l scanning cycles, i t was p o s s i b l e t o compare

C7-262 JOURNAL DE PHYSIQUE

t h e i r r e v e r s i b l e e n t r o p y p r o d u c t i o n f o r each scanning loops. Considering o n l y t h e orders of magnitude, t h e more r e g u l a r s w e l l i n g i s associated w i t h a r a t h e r l i n e a r e v o l u t i o n o f i r r e v e r s i b l e entropy w h i l e d e s o r p t i o n - r e s o r p t i on scannings present an i n f l e x i o n p o i n t around 9 % Hz0 d.b. This may be r e l a t e d t o a change i n c o l l a p - s i n g behaviour (BIZOT e t a1

. ,

1984), o r g l a s s y t o rubbery t r a n s i t i o n (VAN DEN BERG,

1981).

4 5

4 0

* b

³⁵

il

^3,

,.

(11

^{, ,}

'7 E

1 5 .rl

m l n 5

F I G U R E

3 .

I R R E V E R S I B L E ENTROPY PRODUCTION CALCULATED FROM SCANNING CURVES DATA U S I N G FORMULA

2

The n o t i o n o f s w e l l i n g i s n o t e a s i l y c l a r i f i e d by s p e c i f i c volume measurements u s i n g toluene immersion picnometry a t d i f f e r e n t s t a t e s o f hydrations ( F i g u r e 4). H y s t e r e s i s i s o n l y apparent under 10 % d.b. i n t h e l e a s t i d e a l range, w h i l e water and s t a r c h volumes become a d d i t i v e o n l y above 33 % H20 d.b. ( V . HATNE, 1984).

1.10..

1.0s..

1.00 9 5 . .

.9 0 8 5

80 75 70 .65'

spe.vol.

' c r n h g d 4 w g ~ , 0 )

sorption idesorption

..

..

/

.. ^/

/

.. ^/

, / /

60

- /

^{.OS .to is .10 .as .so w .sr Hmg .40 d.b. .4s}

FIGURE 4 EVOLUTION OF lg DRY STARCH SPECIFIC VOLUME WITH HYDRATION AND HYSTERESIS.

X-ray d i f f r a c t i o n diagrams : the A type c h a r a c t e r i s t i c o f cereal starches and the B type o f t u b e r starches. Due t o t h e complexity o f t h e c r i s t a l l o g r a p h i c arran- gements o f t h e chains i n t h e s t a r c h granule and t h e poor q u a l i t y o f X-ray powder diagrams t h e c r y s t a l l i n e o r g a n i z a t i o n o f s t a r c h i s n o t w e l l known. Several models have been used t o approach t h e s t r u c t u r e o f c r y s t a l l i n e p a r t s o f granule, amylose f i b e r s (WU and SARKO, 1978) hydrolyzed starches (CLEVEN, 1978) o r s i n g l e c r y s t a l o f amylose (BULEON e t a l . , 1984), b u t important i n c o n s i s t a n c i e s are s t i l l unre- solved. Water i s necessary t o t h e c r y s t a l l i n e o r g a n i z a t i o n o f t h e granules, t h i s e f f e c t being e s p e c i a l l y remarkable f o r t h e B type as shown o n F i g . 5 , where t h e sharpest diagram (33 % H20) i s indexed f o l l o w i n g t h e u n i t c e l l system o f WU and SARKO (1978). The i n t e n s i t y o f t h e 100 r e f l e x i o n ( 2 @ = 5,6") which corresponds t o t h e i n t e r h e l i c a l d i s t a n c e increases very s t r o n g l y w i t h water uptake. The o t h e r peaks o f t h e d i f f r a c t i o n diagram become a l s o sharper w i t h h y d r a t i o n , along t h e whole adsorption range (BULEON e t a1

.,

1982). A " s t r u c t u r a l h y s t e r e s i s " i s n o t i - ceable s i n c e starch, f o r a same water content, seems t o be more c r y s t a l l i n e i n de- s o r p t i o n than i n adsorption. The non i d e n t i t y w i t h t h e volumic h y s t e r e s i s remains puzzling. This behaviour i s i l l u s t r a t e d by t h e r e s p e c t i v e e v o l u t i o n o f 100 and 121 r e f l e x i o n s i n t e n s i t i e s w i t h water content i n adsorption and desorption on f i g u r e s 6 and 7.

Figure 6 .Evolution of (100) reflexion intensity with water content In adsorption and desorption; I,,, = f (HZOoh); 0 - 0 = desorption. 0 - - - 0 = sorption.

Figure 7. Evolution of (121) reflexion intensity with water content Figure

.

Development ofX-ray diffraction pattern with hydration. in adsorption and desorption: I,z, = f (HzO%): A = desorption.

A = sorption.

JOURNAL DE PHYSIQUE

CONCLUSION

Research advances about water i n t e r a c t i o n o f s t a r c h have n o t been progressing as f a s t as f o r wool k e r a t i n o r c e l l u l o s e probably because fewer t e c h n o l o g i c a l a p p l i c a t i o n s a r e i n v o l v e d on an i n d u s t r i a l s c a l e b u t a l s o because t h e product i t - s e l f i s complex. Up t o now, microscopic examinations, enzymic degradation, s o r p t i o n and c a l o r i m e t r i c measurements and X-ray d i f f r a c t i o n a n a l y s i s have n o t been s u f f i - c i e n t t o g i v e a s a t i s f a c t o r y r e p r e s e n t a t i o n o f t h e g r a n u l a r s t r u c t u r e w i t h t h e r e p a r t i t i o n o f c r i s t a l l in e and amorphous regions.

I n connection w i t h the a n a l y s i s o f s o r p t i o n h y s t e r e s i s on non porous media t h e s w e l l i n g , r e l a x a t i o n and p l a s t i f i c a t i o n o f s t a r c h m a t r i x needs t o be b e t t e r q u a n t i f i e d on an e n e r g e t i c and time scale. A t t h e moment p r a c t i c a l a p p l i c a t i o n s of theses s t u d i e s a r e d i r e c t e d toward g r a n u l a r s t a r c h a c c e s s i b i l i t y i n t h e l i q u i d phase f o l l o w i n g d i f f e r e n t s o l vent sequences. P o t e n t i a1 a p p l i c a t i o n s concern n u t r i - t i o n a l aspects, as w e l l as aroma r e t e n t i o n and m o d i f i e d s t a r c h technology.

REFERENCES

BIZOT H. (1983)

-

I n "Physical p r o p e r t i e s o f Foods" JOWITT R. and C o l l Ed.

Applied Science Publishers. pp 43-54.

BIZOT H., BULEON A., MOUHOUS-RIOU N. and MULTON J.L. (1984)

-

I n " I n f l u e n c e o f water on Food Q u a l i t y and S t a b i l i t y " .

SIMATOS D. Ed., NIJHOFF M. Pub. The Hague, Netherlands. ( t o be p u b l i s h e d ) . BULEON A., BIZOT H., DELAGE M.M. and MULTON J.L. (1982)

-

D i e Starke, 34, 11, -

pp 361-366.

BULEON A., DUPRAT F., BOOY F.P. and CHANZY H. (1984)

-

Carbohydrate Polymers, 4, pp 161-173.

CLEVEN R., VAN DEN BERG C. and VAN DER PLAS (1978)

-

Starke, 30, 223.

EVERETT D.A. and WHITTON 1.1. (1955)

-

Proc. Royal Soc. (London) A 230, pp 91-110.

FRENCH D. (1984)

-

Physical and chemical o r g a n i z a t i o n o f s t a r c h granules. I n

"Starch : chemistry and Technology" 2 nd Ed. chap. 8.

WHISTLER R.L. PASCHALL E.F. and BEMILLER J.N. Eds., Academic Press.

GUILBOT A. and MERCIER C. (1984)

-

"Starch" i n "The polysaccharides". ASPINAL G.O. Ed. Vol. 3. Academic Press. ( t o be p u b l i s h e d ) .

LE MAGUER M. (1984)

-

I n " I n f l u e n c e o f water on Food Q u a l i t y and s t a b i l i t y " . SIMATOS D. Ed., NIJHOFF M. Pub. The Hague, Netherlands.(to be published).

VAN DEN BERG C. (1981)

-

"Vapour S o r p t i o n e q u i l i b r i a and o t h e r water s t a r c h i n t e r a c t i o n s ; a physicochemical approach", Diss. Wageningen.

WU H.H. and SARKO A. (1978 )

-

Carbohydr. Research, 61-7.