On the Dispersion and Small-Amplitude Oscillation Measurements of High Amylopectin Potato Starch

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Starch/Stärke 55 (2003) 121–130 121

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1 Introduction

Although the amylose (Am): amylopectin (Ap) ratio ofmost starch varieties is 20-30:70-80, starches with com-pletely different composition exist. These are either isolat-ed from nature or genetically engineered. Thus, it is pos-sible to find starch varieties which contain more Am (amy-lomaize, high-amylose barley), more Ap (waxy barley), ormore or less only Ap (waxy maize, high amylopectin pota-to starch (HAPP)) [1]. The Am: Ap ratio influences thestarch properties, and several studies have shown that forexample the rheological properties of a starch gel are in-fluenced by the Am: Ap ratio [2, 3].

The rheological behaviour of a gelatinised starch suspen-sion is related to the phase volume of the starch granulesand their firmness [4-6]. However, the amount of leachedmaterial and its nature may also influence the rheologicalproperties of the starch gel or paste [7]. A starch gel maybe regarded as a mixture of granules, more or lessswollen, broken/damaged granules, and a continuousphase of leached material (Am and/or Ap). Depending onconcentration, temperature, shearing during heating, etc.the starch gel may vary in composition of structural ele-ments, from the one extreme with closed-packed swollengranules to the other extreme where the granules havebeen completely dissolved. All combinations in betweenare of course possible. When comparing the rheological

behaviour of starch gels differing in Am: Ap composition itis thus important to be aware of differences in the compo-sition of the structural elements in the gel (describedabove), e.g. differences in the phase volume of swollengranules, the amount of leached material, etc. Moreover,the granule remnants are Ap-enriched structures, whichcould be regarded as swollen hydrated polymer compo-sites, acting as filler particles reinforcing the continuousmatrix of entangled molecules [8-10]. These have beensuggested to induce formation of patterns in the structure[11]. It is well known that the presence of granules orgranule structures strongly influences the physicochemi-cal [12-14], and the rheological properties of the system[15]. A number of studies on starch samples prepared indifferent ways are reported in the literature. Some worksutilised centrifugation [16] or other rigorous treatmentslike the use of sodium hydroxide, dialysis and precipita-tion with acetone [6], or grinding the starch granules witha pestle in order to reduce particle size. When the gran-ules were broken the samples were treated with ultra-sound to break up the Ap, and then heated under stirringat 100 °C [17]. Except for a few published works wherethe idea of dissolving the individual starch polymers pre-sent in granular starch has been mentioned, the differ-ence between starch suspension and starch solution hasusually not been taken into account. Thus, many mea-sured properties reported in literature were probably a re-sult of the presence of granules or granule remains. Nev-ertheless, the effects of granule rests may be eliminatedby a careful disintegration of granule structures in thesample.

Fernando E. Ortega-Ojeda,Helena Larsson, Ann-Charlotte Eliasson

Department of Food Tech-nology, Centre for Chemistryand Chemical Engineering,University of Lund, Lund,Sweden

On the Dispersion and Small-AmplitudeOscillation Measurements of High AmylopectinPotato StarchDifferential scanning calorimetry (DSC), optical microscopy and turbidity measure-ments were used to define experimental conditions (time, temperature and shearing)for dissolving high amylopectin potato starch (HAPP) granules. A simple, less time con-suming and non-chemical method for preparing starch samples was established.Small-amplitude oscillation measurements were used to characterise the behaviour ofthe resulting solutions. The DSC, microscopy and turbidity experiments showed thatpreparing the samples at 140 °C was necessary to dissolve HAPP, with no further de-tectable granule structures. Rheological measurements showed that the storage (G’)and loss (G’’) moduli increased with concentration. At a HAPP concentration of 2 % G’’ > G’ and the system behaved like a diluted solution. The frequency dependencealso decreased with increasing concentration. At 14 % HAPP, the system showedmore gel-like properties with G’ more or less independent of frequency.

Keywords: High amylopectin potato starch; Rheology; Microscopy; Turbidity

Correspondence: Fernando E. Ortega-Ojeda, Department ofFood Technology, Centre for Chemistry and Chemical Engineer-ing, University of Lund, Box 124, S-221 00, Lund, Sweden.Phone: +46-462229670, Fax: +46-462229517, e-mail: [email protected].

Most studies presented in the literature deal with struc-tures in between the extremes described above [2-4].However, the study of rheological behaviour at small os-cillation deformations of Ap in solution, still without molec-ular degradation, need to be more emphasised. In thepresent study the source of Ap was HAPP, which is es-sentially free of Am [1]. HAPP provided us with non-de-graded Ap material. During the work we found that themethods presented in literature for preparing potatostarch gels [2, 3] could not be used to dissolve Ap inHAPP. Therefore, the focus of the present work has beenon the preparation of samples for rheological characteri-sation. We considered it important that the granules wereabsent as they influence the rheological behaviour. Therheological behaviour was also characterised.

2 Materials and Methods

2.1 Materials

Amylopectin (high amylopectin potato starch, <<1 % amy-lose) was provided by Lyckeby-Stärkelsen Food and FibreAB (Kristianstad, Sweden). Bi-distilled Millipore water wasused.

2.2 Methods

2.2.1 Differential scanning calorimetry

The differential scanning calorimetry (DSC) study wascarried out using a Seiko DSC 6200 (Tokyo, Japan). Thesamples were prepared by transferring ~ 10 mg starch-water dispersions (20 % starch, w/w) to coated aluminiumpans (Parts 900790.901 and 900796.901; TA Instru-ments, New Castle, USA), and allowing them to equili-brate for at least 30 min before the DSC run. Al2O3 wasused as a reference. The thermal conditions were: heat-ing temperature range 10 °C – 150 °C, heating rate 5 °C/min, and data-collecting rate 0.2 points/s. The followingparameters were determined for the gelatinisation study:melting enthalpy (∆H), onset temperature (To,gel), peaktemperature (Tp,gel), and final temperature (Tf,gel) of gela-tinisation. The Seiko standard software was used for theevaluation. The reported values are the mean and stan-dard deviation of three repetitions.

2.2.2 Microscopy

For the microscopic study, a drop of a combined suspen-sion of 2 % HAPP and 1 % iodine solutions was placed ina Linkam THMS 600 heating stage, controlled withLinkam LNP and TMS 93 systems (Tadworth, UnitedKingdom). The HAPP suspension was then heated from30 °C to 160 °C at a rate of 5 °C/min, while observed andrecorded on-line in an Olympus BX50 microscope (Tokyo,

Japan), with a 530 nm Olympus U-TP530 polarised lightfilter (Tokyo, Japan).

2.2.3 Sample preparation for turbidity andrheological measurements

For the 20 min heating of the samples, 25-mL high tem-perature-high pressure bottles and a high temperature sil-icone oil bath were used. The bottles had the followingcharacteristics: Tmax ≤ 200 °C; GL25 (Duran, SCHOTT,Mainz, Germany). The oil had the following characteris-tics: Tmax ≤ 180 °C, 0.98 g/m3 density (20 °C), 370-390mPa s viscosity (20 °C) (Fluka, Stockholm, Sweden). Af-ter heating, the sample was quenched (4 s) with gentlestirring in a water bath, at 30 °C for the turbidity measure-ments, and at 60 °C for the rheological measurements.Immediately before the rheological measurements, thesamples were transferred to the geometry of the con-trolled stress rheometer system, and studied at 50 °C forthe viscosity measurements or 10 °C for the other tests inoscillation.

2.2.4 Turbidity

For the study of the temperature dependence of turbidity,3 g samples of HAPP suspensions (3 % and 6 %, w/w, re-spectively) were heated at different temperatures (95-150 °C) without stirring. The samples, once in the mea-suring cells, were degassed for 10 s in a Branson 220 ul-trasound bath (Bransonic, Shelton, USA) at 25 °C. Theabsorbance of the suspensions at 650 nm was immedi-ately measured every 10 s for 1 h in a Hitachi U-1500Spectrophotometer (Tokyo, Japan) at room temperature.The reported values are the mean and standard deviationof three repetitions.

2.2.5 Rheological measurements

For checking the influence of heating temperature on theviscosity of the solutions, 16 g samples of HAPP suspen-sions (0.5 %, w/w) were heated at 90, 130, 135, 140, 150,and 160 °C, without stirring. The viscosity measurementswere performed in the rheometer (StressTech, ReologicaAB, Lund, Sweden), with the CC 25 concentrical cylindersystem measuring every 15 s using the following param-eters: stress 0.57-37 Pa, delay time 30 s, integration peri-od 11 s. The flow curves were performed in the shear rateregion 1.12 · 10-2 – 1.84 · 103 s-1. All the reported valuesare the average of at least three different runs and samplepreparations.

The small-amplitude oscillation measurements were per-formed in the linear viscoelastic region (determined fromstress sweep experiments, not shown) using the C40 4cone and plate geometry in a continuous mode, perform-

122 Ortega-Ojeda et al. Starch/Stärke 55 (2003) 121–130

ing small-amplitude oscillatory measurements every 10 sduring 6 h. The conditions of the system were: strain0.025, frequency 0.2 Hz, continuous mode, delay time5 s, integration period 1 s. The reported values are themean and standard deviation of three repetitions.

For the study of the influence of shear during samplepreparation, 5 g of HAPP in water (6 %, w/w) were heatedat 140 °C. During the heating time, the following shearingconditions were used for 30 s, every 2 min: no shearing,intense manual stirring (hand shaking), 200, 400 and 600rpm on the magnetic stirrer. The magnetic stirring wascarried out in a low power magnetic stirrer (Baird & Tat-lock, Chadwell Heath, England) with a reversing period of7 s.

In order to study the curing behaviour, samples of 3 – 5 gHAPP suspensions (2, 6, 8, 9, 10, 12, and 14 % HAPPconcentrations) were heated at 140 °C for 20 min withgentle stirring every 2 min. With HAPP concentrationsabove 10 %, 30 min were used as holding time instead ofonly 20 min, due to the difficulty of dispersing the gran-ules. The stirring was done in order to obtain a homoge-neous distribution of the sample (remixing of the con-densed water) in the heating bottle. For comparison, asample of 5 g HAPP suspension (2 %) was heated usinga water bath at 90 °C during 20 min. The small-amplitudeoscillation measurements were performed on the sam-ples with the C40 4 cone and plate geometry as describedbefore.

3 Results and Discussion

DSC, microscopy and turbidity data were examined tofind an adequate dissolution method for the HAPP gran-ules. Once the preparation method was established, therheological properties of HAPP solutions prepared ac-cording to this method were characterised.

3.1 Method for dissolving HAPP-granules

3.1.1 Differential scanning calorimetry

Similar to earlier observations for potato starch at lowstarch concentration (< 40 %)[18-20], HAPP showed onlythe single non-broad and well defined DSC G-endotherm.∆H was 19.7 J/gAp, and To,gel, Tp,gel and Tf,gel were 62.3,66.6 and 70.7 °C, respectively. These values for HAPPwere somewhat higher than values obtained for potatostarch investigated at the same conditions. ∆H was then16 J/gAp, and the corresponding temperatures were 57,62 and 68 °C, respectively [21]. This result agrees withthe observation that the thermal stability of HAPP is high-er than that of potato starch [1, 22].

3.1.2 Microscopy

Fig. 1 shows the 2 % HAPP sample heated from 30 °C to160 °C. HAPP was stained by iodine in light red, with fewswollen core granules stained in blue-purple indicatingthe presence of small amounts of Am. This mode of stain-ing has previously been reported for normal Am as well asfor HAPP [14, 23]. HAPP granules started to swell ataround 50 °C and break down at around 60 °C. Thisprocess seemed to be fast between 62 °C and 64 °C,where plenty of granules swelled and broke down sud-denly. The swelling and rupture of granules continued upto 78 °C, after which the rupture of granules decreaseddrastically, leaving numerous already swollen and stillbirefringent granules (presence of the Maltese cross).Heating at 90 °C was reported to be enough to dissolve“normal” potato Ap [2]. However, in case of heating HAPPa large amount of granules continued to swell and breakdown further when the temperature was increased be-yond 90 °C (Fig 1). Birefringence of some granules wasevident up to 86 °C. Even though it appears that there areno significant differences between the X-ray diffractionpatterns (B-type), or crystallinity between normal potatoand the HAPP used in this work [24], it seems that thegranules exhibited increased thermal stability.

The granule remnants shown in Fig. 1, known to con-tribute to the rheological behaviour of the suspension(see below), were detected up to approximately 130 °C.At higher temperatures than 130 ºC, or more markedlybeyond 140 °C no changes in microscopic appearancewere detected, and hence after heating to 140 °C thesample was considered to be in solution as no granuleremnants could be observed (Fig. 1). Interestingly, a sim-ilar behaviour, a slight haze present in final starch solu-tions even after rigorous treatments, has been reported inthe literature for normal potato starch [6]. The behaviourof the granules during heating observed by microscopyfollowed the DSC results in that most of the granuleswelling occurred within the temperature range of theDSC-endotherm. However, many remaining intact gran-ules were detected beyond 80 °C, immediately after theDSC peak was passed. Furthermore, granule remnantswere also present at temperatures much higher thanthose corresponding to the end of the crystallinity meltingpeak (110 to 130 °C, for instance).

3.1.3 Turbidity

Fig. 2 shows the turbidity measurements for HAPP sus-pensions (3 % and 6 %, w/w), treated at different temper-atures for 20 min. In general, the lower the preparationtemperature and the higher the concentrations of theHAPP suspension, the higher were the absorbance val-ues. The highest absorbance values were observed for

Starch/Stärke 55 (2003) 121–130 On the Dispersion and Small-Amplitude Oscillation Measurement … 123

samples treated at 95 °C (3 %) or 95 – 100 °C (6 %). Forall the temperatures, the absorbance values decreasedonly slightly during the observation time (the slope of thecurves). However, the absorbance decreased uniformlywith increasing preparation temperature up to 130 –

150 °C (3 %), and to 140 – 150 °C for the 6 % suspensionwhere no further decrease in absorbance was observed.In other words, for both concentrations the absorbancevalues were not reduced further when heating to temper-atures above 140 °C.


Fig. 1. Microscopic sequence for 2 % HAPP heated from 30 °C to 160 °C. The bar is 60 µm.

40 °C 50 °C 60 °C 62 °C

64 °C 68 °C 69 °C 70 °C

72 °C 78 °C 86 °C 90 °C

95 °C 100 °C 110 °C 120 °C

130 °C 140 °C 150 °C 160 °C

3.1.4 Flow curves

In order to evaluate the influence of the sample prepara-tion temperature on the viscosity of the HAPP suspen-sions, the flow curves of a 0.5 % HAPP suspension, wereproduced. The data was fitted to the Ostwald-de Waele(power-law) model (Tab. 1), σ = kγ·n or η = kγ·n–1, where σis the shear stress, γ· is the shear rate, η is the shear vis-cosity, n is the power law index, and k is the consistencyindex. All the samples, except the one prepared at160 °C, showed a tendency to be shear thinning (n < 1)(Tab. 1). The slope of the curves decreased slightly whenthe temperature increased, thus the behaviour of the sus-pension approached that of a Newtonian fluid when thepreparation temperature was increased to 150 °C, i.e., nincreased towards unity, while k decreased, resembling amore water-like system. In all the cases, the shear vis-cosity levelled off at around 0.01-0.02 Pa s at the highestshear rates. The viscosity measurements showed that thepreparation temperature affected the properties of HAPPsamples. Whether the effect on the flow curves was a re-sult of dissolution of aggregates or hydrolysis of mole-cules could not be established. Because no majorchanges (from granular HAPP to a non-detectable pres-ence of granule remnants), observed in the microscopy,absorbance and viscosity of the systems, took place attemperatures between 130 and 140 °C, all further sam-ples were prepared at 140 °C.

3.2 Small-amplitude oscillation measurementson HAPP samples without visible granuleremnants

HAPP samples of different concentrations (2-14 %, w/w)were prepared by heating at 140 °C for 20 min with man-ual shaking. Manual stirring was selected from shearingexperiments (data not shown), as remixing the con-densed water inside the preparation bottles was consid-ered important for the reproducibility of results. Fig. 3shows the values of G’ and G’’ at 0.2 Hz after 6 h of cur-ing for the different concentrations of HAPP. The insertshows G’ and G’’ of the HAPP solutions during the whole6 h period. The standard deviation was maximum30 mPa. No changes in G’ or G’’ were registered duringthe six hours curing period. The samples were visuallyclear and showed no optical inhomogeneities as hasbeen reported for the turbid Ap gels [25]. Besides, thesystem was remarkably stable compared to systems con-taining granules, where the moduli are known to increaseduring the first hour and after which they continue to in-crease although to a lesser extent [6, 9]. The G’ valueswere low (< 7 Pa) for HAPP. This may be compared withvalues reported for other starch gels like potato (~ 400Pa) and tapioca (~ 200 Pa), for example [13, 15]. More-over, for each concentration in the range 2-10 % HAPP,G’ and G’’ had approximately the same values (Fig. 3, in-sert). Nevertheless, both G’ and G’’ tended to increasewith concentration. At higher concentrations (≥12 %), G’was greater than G’’, and more affected by concentrationthan G’’. In other words, G’ was not only larger than G’’with increasing HAPP concentration, but also the G’/G’’ratio increased above a concentration of 10 %. A non-lin-ear relationship thus seemed to appear between G’ andconcentration when the HAPP concentration was higherthan approximately 10 %.

This behaviour differs from previous reports where a lin-ear relationship was seen in the range 10-25 % Ap [25].Moreover, other studies reported that the potato Ap con-centration necessary for G’ to be larger than G’’ was 5.9 %


Fig. 2. Turbidity measurements on HAPP suspensions (a:3 %, and b: 6 %) treated at different temperatures for 20 min with weak and intermittent agitation. λ = 650 nm.–■ – = 95 °C, - -◆ - - = 100 °C, - -▲- - = 110 °C, - -● - - =120 °C, - -×- - = 130 °C, - -● - - = 140 °C, - -+- - = 150 °C.

Tab. 1. Parameters for the Ostwald-de Waele (power-law)model for 0.5 % HAPP treated at different temperatures. r was 1.00.

T k n[°C] [mPa sn]

90 450 0.44130 262 0.54135 154 0.60140 74 0.66150 52 0.69160 2 1.02

[17], or above 20 % [26]. However, the preparationmethod was not described in detail. It must be mentionedthat in the present work HAPP concentrations higher than14 % could not be used because the mixtures could notbe stirred under the same conditions as the other sam-ples. Moreover, with the concentrations used in the pre-sent study, and in the time scale of the experiments, theHAPP suspensions did not show any visible phase sepa-ration or inhomogeneities (the system remained clear),and may thus be interpreted as being more stable thanthe corresponding normal potato starch systems, whichhas been observed elsewhere [14]. The microscopy studyshowed that the HAPP samples used for the rheologicalmeasurements in the present work have no remaininggranule structures. Interestingly, HAPP samples showedclarity, low values of the moduli, and absence of changes

in G’ and G’’ during the long curing time. Low moduli val-ues and slight changes in the moduli during curing timehave also been reported for monodisperse Am [27]. Con-sequently, since no turbidity or phase separation was de-veloped, further aggregation should not result in crystalformation.

Fig. 4 shows the frequency sweeps for samplescontaining 2-14 % HAPP, after 6 h of curing. The insertshows the slope values for these frequency sweepcurves. For all concentrations, G’ and G’’ converged withincreasing frequency, and the frequency dependence de-creased with increasing concentration. However, forevery concentration between approximately 6 and 12 %,G’ was almost equal to G’’ over the whole frequencyregion (0.0001-10 Hz). Similar frequency response has


Fig. 3. Moduli values at 0.2 Hz af-ter 6 h of curing for differentHAPP solutions treated at 140 °Cfor 20 min with gentle shearingand quenched from 60 °C to10 °C. ■ , ■■ = G’ and G’’, respec-tively. The insert shows the be-haviour with time of the differentHAPP solutions. ■ , ■■ = 14 %; ● ,●● = 12 %; ▲, ▲▲ = 10 %; ▼, ▼▼ =9 %; ◆ , ◊ = 8 %; �, �� = 6 %; �, �� = 2 %. Closed symbols arestorage modulus (G’), and opensymbols are loss modulus (G’’).The standard deviation was30 mPa as maximum.

Fig. 4. Frequency sweep forHAPP solutions treated at 140 °Cfor 20 min with gentle shearingand quenched from 60 °C to 10°C. ■ , ■■ = 14 %; ▲, ▲▲ = 10 %; �, �� = 6; �, �� = 2 %. The insertshows the slope values of the fre-quency sweep tests. ● = slope ofG’ and ●● = slope of G’’. Closedsymbols are storage modulus(G’), and open symbols are lossmodulus (G’’).


been reported for modified starches such as hydroxy-propylated phosphate crosslinked potato starches (HPS). In these samples many granule remnants were observed although samples were prepared under heavy heating conditions (20 – 100 °C) [9, 28-30]. In thepresent study, the values of G’ and G’’ were dependent on frequency for HAPP concentrations <14 %. The values of G’ for the highest HAPP concentration were also lower than the reported values of G’ at the minimumconcentration required for G’ to be larger than G’’ [31].This may imply that the external branches of the Ap mol-ecules have been shortened somehow, and thus hinder-ing the polymer to establish stronger and more stableinteractions with each other. It can be seen that very lowfrequencies are needed to observe gel-like properties at 14 % HAPP. Thus the necessary relaxation time for the system is very long, of the order of at least 104 s.

A true gel has been defined as a soft, solid or solid-likematerial composed of two or more components where

one is a liquid, in significant amount. In addition, a solid-like gel has no equilibrium modulus as solid materialshave, which means that G’ for a solid-like gel will de-crease at a relatively long experimental time. However, G’for a solid-like gel has a pronounced plateau extending totimes at least of the order of seconds, while G’’ is muchsmaller than G’ at the plateau [32]. For a gel, generally thevalues of G’ and G’’ are more or less independent of fre-quency [31, 33]. In a frequency sweep experiment, G’ andG’’ show power law behaviour, with the relationship: G' =G'0 f n' and G“ = G'0 f n' , where G'0 and G“0 are the inter-cepts, and n’ and n’’ are the slopes of the log(G’, G’’) vs.log f mechanical spectrum, respectively [31]. The magni-tude of the slopes gives useful information. It has beenmentioned that for a dilute polymer solution G’ should beproportional to f 2 and G’’ should be proportional to f 1 [31].We can see that for a true gel system, passing from a solto a gel (a three-dimensional network), the slope valuesare expected to vary from 2 to ~ 0 for G’ and from 1 to ~ 0for G’’. The nonzero power-law slope may be due to the

Fig. 5. Effects of two different temperaturetreatments (90 °C and 140 °C) on the rheolog-ical properties of 2 % HAPP samples; a showsthe moduli values at 0.2 Hz after 6 h of curing,b shows the frequency sweep for the samples.✴ G’, + G’’ at 90 °C; � G’, �� G’’ at 140 °C.Closed symbols are storage modulus (G’), andopen symbols are loss modulus (G’’).

presence of both crosslinked and uncrosslinked poly-mers, and increasing values show the presence of in-creasing fractions of uncrosslinked material [34]. In the in-sert in Fig. 4, it can be seen that the values of the slope ofthe frequency response decreased abruptly with increas-ing concentration to obtain more or less constant valuesat concentrations of 6-10 %, i.e. from ~ 1.55 to ~0.55 Pa/Hz for G’, and from ~ 0.85 to ~ 0.55 Pa/Hz for G’’.This ‘steady’ behaviour lasted until the concentration wasincreased to ~ 10 %, where G’ and G’’ were on the samelevel. Increasing the concentration even further, the gel-like behaviour increased and the slope values decreasedeven further, especially for G’ which approached the val-ue of zero (Fig. 4). However, although G’ was more or lessindependent of frequency (n’ ~ 0) at the highest HAPPconcentrations ~ 14 %, the terminology ‘strong’ gel seemsnot to be appropriate for describing the HAPP weaknetworks. This mainly because the values of G’ were low,< 7 Pa.

Fig. 5 shows a comparison of the effect of the tempera-ture treatment (90 °C or 140 °C) on the rheological prop-erties of 2 % HAPP samples. The sample treated at 90 °Cshowed weak gel-like behaviour, with a difference be-tween G’ and G’’ of about one unit. Although the modulivalues were quite low (~2 Pa and ~1 Pa for G’ and G’’, re-spectively), G’ and G’’ were still higher than those cor-responding to the 2 % HAPP sample treated at 140 °C,which did not show starch structures. For the sampletreated at 90 °C, the gel-like behaviour was observed at0.0001 – 10 Hz. For the low temperature treatment wherestarch structures were present, G’ at the lowest frequencywas almost seven decades larger than the value for thehigh temperature treatment.

4 Conclusion

It has been shown, by DSC, microscopy and turbiditymeasurements, that 140 °C was the most appropriatetemperature for reducing the influence of granules inHAPP samples on the rheological measurements. At thistemperature, no granule structures were detected in themicroscope. In the small-amplitude oscillation measure-ments, the system proved to be stable with time, showingno syneresis. In addition, the moduli showed a concentra-tion dependence, and the concentration where G’ waslarger than G’’ was beyond 10 %. At concentrations high-er than 10 %, the system behaved more gel-like than atlower concentrations. For all concentrations, G’ and G’’converged with increasing frequency. At concentrationslower than 14 %, the frequency dependence decreasedwith increasing HAPP concentration. In addition, G’ andG’’ augmented with increasing concentration. In the con-centration range 2-14 % HAPP, diluted solution to gel-like

behaviour was observed. We have also shown that whenthe granules or granule structures are eliminated, the fre-quency of the 2 % HAPP sample is changed from thatcorresponding to a weak gel (sample prepared at 90 °C)to the one of a diluted solution (sample prepared at140 °C).

Acknowledgement

Financial support was obtained from the Centre for Am-phiphilic Polymers for Renewable Resources (CAP) atLund University.

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(Received: July 15, 2002)

(Accepted: September 16, 2002)

On the Dispersion and Small-Amplitude Oscillation Measurements of High Amylopectin Potato Starch

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