Impact of crystallinity indexon the stability and physical properties of inulin du ring moisture uptake

Sébastien N. Ronkartl•2, Michel Paquot',Christian Fougnies', Claude Deroanne? and Christophe Blecker?

1 Gembloux Agncultural University. Dcpartmcnt of Food Technology (Head: Prof. C. Dcroanne). URL: hnp://www.fsag; x. ac.be/ta2 Gcmblou x Agricultural University. Dcpartmcnt of Industrial Biological Chcmtstry (Head: Prof. M. Paquet).

Passage des Déportés. 2. 8-5030 Gembloux. Bclgium.3 Cosucra Groupe Warcoing SA. Rue de la sucrerie. 1.8-7740 Warcoing. Belgium

mcosucraGroupe Warcoing

IntroductionInulin ill a natural storage carbohvdrate ccmpesed of a chain of fructose units with gencrally a terminal glucose unit, industrially extracted (rom chieor)' root and commercially available in the pcwdered Iorm. ln thefood tcchnolo~' domain, the study of the amerpheus fraction by the mean of the glass transition temperature (TI) i crucial for prcdicting powder tability during storage. Unlike crystalfine structure. an amorphousis in a non-cquitibrium state and "ill tend to Crf!taIli7..c depcnding on storage condition! (temperature, humidtty). ln thi! study, the impact of the cr)'!tallinity of spray-drjed inulin on the pewder stability WaJ

invesrigatcd during water uptake at 94-/. relative humldity (RH) sterage at 20"C. Various spray-dried inulin powders with different cr)'!tallinit), indexe! but with identical chemical composition were used for thispurpose. The resutting physical prcpcrties and pewdcr stability of inutins were studied in detail at varieus water content. The plasticizing effect of water on glass transition temperature (Til) and cr)' tallinity wascharacterlzed by Modulated Differentiai Scanning Calortmetry (MDSC) and Wide Angle X-ray Diffraction (WAXS). rcspcctivcly. Tcmperarure-resolved WAXS "'85 used to cerrelate the MDSC thermograms and theWAXS diffractograms when crystallizarien oeeurred in both amerpheus and semi-crystalfine inulins. ln addition, the inter-particular nrcoenlcs whieh were related to the powder stability were vlsuafized byEnvircnmcntat Scanning Electron Microscop)' (ESEM).

Amorphous inulin

MDSC in open pans

:;~Tg13.6 -

14.8

15"7~:~~I:::-r120 140 160 180

Temperature (0C)

Crystallinity development

9 14 19 24 19Diffraction angle (2 theta)

The samples wcre considered complctclyamorphous up 10 a watcr content of 15.7 gwatcr 1100 g dry inulin (crystallinity index-oe/.): while crystallization occurred bctwecn15.7 and 16.3 g watcr 1100 g dry inulin. The

crystaltinity indexes increased up to 92·93%at l â.â g water é lêê g dryinulin.

Up 10 13.6 g water 1 100 g dry Înulin.amorphous inulin only prescnrcd a gtasstransition al around 150°C. Althoughlhe samprcs at 14,8 and 15.7 g warer 1100 g dl)' inulin were still arnorphous.their thermal properties were differentfrom thosc contairung up to 13,6 gwater 1 100 g dl)' inulin. Above 16,3 gwatcr /100 g dry inulin. an endothermicpeak was present around the gtasstransition temperature.

ESEM micrograph ofamerphous inulin in Zone 1

amcrphous inulin in Zone III

\ "};~ ~.',~. .--

-f -'\,Amorphous inulin in zone 1wes in a powdcr form: whilcamorphous inulin in zone IIIcakcd. Thc drop of thematerial's viscosity led 10imcr-particles fusion andrhus the caking of thepowdcr.

Temperature Resolved W AXS

25 50 75 100 125 150 175200Température eC)

Tcmpcrarure-Resolved WAXS ofamorphous inulin storcd one weck al94% RH (wetcr content •• 18,9 g watcr1 100 g dry inulin). Vertical linescorrespond 10 the onscr, midpoint andcndset temperature of the MDSCcndothcrmic peak.

Experimentation and results

Tg - water content state diagrams ofamorphous and semi-crystalline inulins

Scrni-crystaüinc inulinAmorphous inulin __ ~ 6160 25

20

Semi-crystalline inulin

::~~Kmi·cr.n.t:tllincinulin inZoM 111 16.1 ~~

15.1

14"0--'-1\-~_ -0"6;::~=....;::_\../__ -_ "_" ~__ ~

Up 10 7.9 g waret 1 100 g dry inulin,scmi-crystaüine inulin wascbaractenzcd by a dual endothennicpeak. which correspondcd 10 themetting of a dual crystal population,Between 7,9 and 10.1 g water /100 gdrv inutin. and additional endothcrmicpeak eppearcd al 157°C. whichcorrcspondcd 10 the metting of crysralsformcd (sec W AXS resutts) .

ESEM mtcrograph ofsemi-crystalllne inulin in Zone 1

Semi-crystallinc inulin inzone 1 was in a powdcr form;while scmi-crystallinc inulinin zone 111 was slightlyagglorneratcd but the entireproduel was casily friablc.

20

ISO

M OSC in open pans

120 140 160 180Temperature (0C)

Crystallinity development

9 14 19 24 29Diffraction angle (2 theta)

The scmi-crystelline inulin rccrystalhzed al alower water content than the amorphouscounrcrpart.

Temperature Resolved WAXS

120

Temperarurc-Rcsolvcd WAXS ofscmi-crystalline inulin stored oneweek at 94% RH (watcr content ".20.8 g water 1 100 g dry inulin).Vertical lines correspond 10 the onser,and endset temperature of the MDSCendothcrmic peak eentered al 170°C.

120 140 160Température (oq

ln companson ro the MDSC rcsults. the beginning and the end of the endothennic peak corrcsponded to the transition ooscrved in theTempcraturc-Resotvcd Wîde Angle X-ray Scattertng expcrimenr (145 and 165°C for onset and cndser tempcrarure. respectivcty). Indecd. upto 145°C. crystattizcd amorphous inulin showed diffraction peaks; while above this value. the crystallinity dccreased drastically. as showedby the drap of the crystallinity index, A completely amorphous samplc was observed at 166°C. Semi-œystaüine inulin exhibitcd a totallostof crystalliniry 12°C higher than its amorphoos counterpan.

III

13,5

50 75 100 125 ISO 17.5 200Température COq

The effect of wetcr content on amorphous and scmi-crvstalline inulin properncs was lnvestigated, Water content, crystalfinhy indexes. thermal propcrtles and glass transition temperature evelutien perrnitted theunderstandlng of the physical and behavtor changes of both powders. During watcr uptake, amorphous powdcrs cakcd: white the scmi-crystathne counterparts were agglomerated but friable. Both caking andagglomeration were cbscrved ",hen the TI was belon' the 200C stonlgc temllcrature. This led to a higher mobilit), of the amOrlJhous fraction of the powder and an increase of the crystallinit)' for both semi·cr)'stalline andamorphous inulin. The eXllCrimentations ha,'c shown that the semi·cr)'stallinc inulins were stabler in thc high humidit), environment than the amorphous oncs; which i~ of erueinl imlJortance for the Stllbility of inulinduring proeess. storal,'C or incMlloration in high moisture formulations. The TI- water content state diagram of amoqlhous inulin ullowed us to point out thrce zones. Zone 1 WllS the plasticization dfeet of water on TIwith inulin in a Ilowdercd amorphous state. The defined zone Il WllS an intermediate state betwcen ghlSS)' amorphous llnd erystallizcd inulin. with some macroscopic und thermal prollCrt)' changcs. ln zone III, theproduci cr)'stnIli7.cd. caked and no glass transition was observed. An endothcrmic IlCak allilcared at the initial glass transition, whieh was attributed to the melting of inulin erystals, as confirmed b)' Temperature-Resoh·cd Wide Angle X·ra)' Seattering.

100

~" 80...

60

40

1\ ::~ __ ~~"~'~'-ll~~ --~Oo 5 10 15 20 25

water content (g water/1OO g inulin)

The retationship bcrwccn water content. crysteützaticn andthermal propertics. pcrmiued the determination of thrèc zonesin the state diagram.

Zone 1 was the ptasricizaricn effcct of warer by deprcssing Trwitbout physical property changes like heat capecity jump.crystaltinity index or caking as the product was still in apowder form.

Zone )) cbaractcrizcd the product with a TI down 10 thestorage temperature with some macroscopic and thermalproperty changes, bUI with a crystallinity index cqual 10 zeroas in zone 1 (for amorphous inulin). Moreovcr. in the fullyamorphous samples. sorne parts of the amorphous phase wererubbcry and ethers wcrc in the powdercd forrn. ln zone II.some pans of Ihe scnu-crystaütnc of the samplc wcreagglomcrarcd but casily friable and ethers were in thepowdered forrn.

Zone III cbaractcrtzcd a Irœ Ilowing 1055 for borh amorphousand semi-crystaüinc mutin. Amorphous Înulin caked (hard andbrittle): while scmi-crystalline inulin agglcmcrated (but easilyfriable).

100 •

:;; 80

.-.•..6.olo~ ••••

.•. '.Amorphous inulin 60

61_---.-..

Scmi--cryslalline~_

AcknowledgmentsFinancial suppon was pfO\idcd for this stndy by the Walloon Region of Belgium (DGTRE) and Cosucra Groupe Warcoing SA. The authors are graleful to Mrs Lynn Doran for lechnical assistance. Mrs. Bernadette NoJberg and Prof. JohanWoutcrs from Ihe . Dcpanment of Structural Biological Chcmistry' of the 'Facultés uni\"ersitaircs NOire Dame de la Paix' (Namur. Belgium) for lhe use of the WAXS and the Temperalure·Rcsol\'ed WAXS. and Jcan-Christophc Lambrechtsfrom the CERTECH (Seneffe. Belgium) for his help on ESEM,

-l:.s 60z-~ 40

Ë·u 20

o100

Conclusions

Impact of crystallinity index on the state diagram of inulin during

moisture uptakeSébastien N. Ronkart1,2, Michel Paquot/,

Christian Fouqnies'', Claude Deroanne 1,Christophe Blecker",

1,2Gembloux Agricultural University, 1Department of Food Technology; 2Department

of Industrial Biological Chemistry, Passage des Déportés, 2, B-5030 Gembloux,

Belgium.

3 Cosucra Groupe Warcoing SA, Rue de la sucrerie, 1, B-7740 Warcoing, Belgium.

ln the food technology domain, the study of the amorphous fraction by the mean of

the glass transition temperature (Tg) is crucial for predicting powder stability during

storage. Unlike crystalline structure, an amorphous is in a non-equilibrium state and

will tend to crystallize depending on storage conditions (temperature, humidity). ln

this study, the impact of the crystallinity of spray-dried inulin on the powder stability

was investigated during moisture uptake at 94% relative humidity (RH) storage at

20°C. Various spray-dried inulin powders with different crystallinity indexes but with

identical chemical composition were used for this purpose. The resulting physical

properties and powder stability of inulins were studied in detail after various storage

times at 94% RH. The plasticizing effect of water on glass transition temperature (Tg)

and crystallinity was characterized by Modulated Differentiai Scanning Calorimetry

(MDSC) and Wide Angle X-ray Diffraction (WAXS).

During moisture uptake, amorphous powders caked; while their partially crystalline

counterparts were agglomerated but friable. Both caking and agglomeration were

observed when the Tg was below the 20°C storage temperature. This led to a higher

mobility of the amorphous fraction of the powder and an increase of the crystallinity

for both partially crystalline and amorphous inulin. The experimentations have shown

that the partially crystalline inulins were stabler in the high humidity environment than

the amorphous ones; which is of crucial importance for the stability of inulin during

process, storage or incorporation in high moisture formulations.

Keywords: inulin, caking, x-ray diffraction, glass transition