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Food Hydrocolloids 23 (2009) 2388–2393

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Food Hydrocolloids

journal homepage: www.elsevier .com/locate/ foodhyd

Sweetness and texture perceptions in structured gelatingels with embedded sugar rich domains

Karin Holm a,b,c, Karin Wendin b, Anne-Marie Hermansson b,c,*

a Nordic Sugar AB, SE-205 04 Arlov, Swedenb SIK AB – The Swedish Institute for Food and Biotechnology, P.O. Box 5401, SE-402 29 Goteborg, Swedenc Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Goteborg, Sweden

a r t i c l e i n f o

Article history:Received 13 June 2008Accepted 23 June 2009

Keywords:GelsGelatinSweetnessSugar distributionRheology

* Corresponding author. Tel.: þ46 (0) 10 516 66 58E-mail address: amh@sik.se (A.-M. Hermansson).

0268-005X/$ – see front matter � 2009 Elsevier Ltd.doi:10.1016/j.foodhyd.2009.06.016

a b s t r a c t

Layered and homogeneous gelatin gels with controlled rheological properties were compared for theirsensory characteristics, specifically sweetness, hardness, breakdown behaviour and frothing. All gels andlayers had a gelatin/water concentration of 5%. The total sugar concentration was 9% in the layeredsamples and 0, 9, 15 or 22.5% in the homogeneous samples. These concentrations corresponded to theconcentrations in the single layers.

A seven-layered sample with different sugar concentrations in the layers gave a higher early sweetnessintensity than a homogeneous gel with the same mean total sugar concentration. All layered gels weresimilar in hardness, breakdown behaviour and frothing; for the homogenous samples, sensory hardnesswas decreased in samples with much sugar. These gels also fell into smaller pieces than the sugarlesssample. This study shows that it is possible by controlling the sugar distribution within a sample toproduce sweeter gels while the sugar content is maintained.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

There is an increasing demand for sugar reduced and/or fatreduced foods with retained properties of taste, texture and flavour.Sugar is often used as a bulk chemical, i.e. added in large amountsto foods, and contributes to sweetness and texture properties.A change in sugar content may therefore both change the percep-tion of sweetness and of texture.

One possibility for optimization of the perceived sweetness is todistribute taste molecules differently within a structure andthereby alter the sensory profiles. In the present work the effects ofsugar distribution in a layered gelatin structure have been studiedwith regard to the sensory perceptions of sweetness and texture.Gelatin is a commonly used thickener in foods, for example indesserts, jellies and dairy products, and is a protein derived fromcollagen, which is the primary protein component of animals’connective tissues (Ramachandran, 1967). Gelatin forms thermo-reversible gels upon cooling by association of the amino acidsglycine, proline and hydroxyproline (Ledward, 1990), and one of themost common properties that are taken advantage of is its mouth-melting properties, which distinguishes gelatin from most other

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food thickeners (Johnston-Banks, 1990). The melting temperatureof gelatin is w35 �C and can be influenced by the Bloom value andgelatin concentration as well as by the presence of other ingredi-ents, such as salts, sugars and other gelling or thickening agents(Johnston-Banks, 1990). Gelatin gels are formed as entanglementnetworks, with inbound flexibility. At low gelatin concentrations,the flexibility affects the over-all properties of the gels but, as thegelatin concentration increases, the flexibility in different entan-glements may level out.

Gelatin form gels in the absence of sugar, but addition of sugarhave been reported to increase the gel strength of 7% (w/w) gelatingels, which is in contrast to many other thickeners where thestructure becomes less strong by sugar addition (Kasapis &Al-Marhoobi, 2003). In many studies, the total gelatin concentra-tion is specified and kept constant, for which reason the sugaraddition actually increases the effective gelatin concentration. Inthe present study, we have corrected the gelatin amount foraddition of sugar and prepared gels with a constant gelatin to waterconcentration, irrespective of sugar concentration.

Sweetness in gelatin gels has been found to decrease withincreasing gelatin concentration (DeMars & Ziegler, 2001; Moritaka& Natio, 2002), although the decrease was much smaller comparedto other thickeners (Moritaka & Natio, 2002; Wendin, Solheim,Allmere, & Johansson, 1997), plausible due to its melting propertieswhich enhances transport of tastants to the receptors (Moritaka &

K. Holm et al. / Food Hydrocolloids 23 (2009) 2388–2393 2389

Natio, 2002), and the relation between sweetness and gelatinconcentration was believed to be inversely proportional (DeMars &Ziegler, 2001). The decrease in sweetness is probably related toa higher density and more cross-linking domains in gels withhigher concentrations (Moritaka & Natio, 2002; Morris, 1994).Increased gel rigidity/strength in gelatin gels has been found tocause a decrease in sweetness intensity (Boland, Delahunty, & vanRuth, 2006; Wilson & Brown, 1997). However, when gelatin wasused as a fat replacer in sour milk applications, it did not affect thesweetness perception (Wendin et al., 1997).

Results have been reported on the effect of the distribution ofNaCl on the perception of saltiness; increased aqueous concentra-tion of NaCl in o/w emulsions enhanced the salty taste (Metcalf &Vickers, 2002; Yamamoto & Nakabayashi, 1999), but similar NaClconcentration in a water solution and an emulsion’s aqueous phaseresulted in equal (Metcalf & Vickers, 2002) or lower (Yamamoto &Nakabayashi, 1999) salty taste as compared to a pure solution.These results concerned liquid systems with oil, but it is reasonableto assume that the same relations will be valid for gels.

In a previous study of the perception of sweetness in mixedLM/HM pectin gels, we showed that hardness was not the onlyparameter affecting sweetness intensity. Also the pectin type isimportant and gels with higher proportions of LM pectin wereperceived as sweeter. By mixing pectins it is possible to producesweeter gels with similar hardness (Holm, Wendin, & Hermansson,2009). An experimental design was used based on gels with similarrheology, but different total pectin concentrations, and gels withdifferent rheology but similar total pectin concentration.

Also in this study gels were produced with similar viscoelasticproperties. The aim was to establish how sweetness, hardness,breakdown behaviour and frothing varied in gelatin gels that hada constant gelatin/water concentration but varying sugar concen-trations. Gels were produced with the same total sugar concen-tration, but with the sugar differently distributed in the structuresby a layer-by layer building process.

2. Materials and methods

2.1. Material

Type A gelatin from porcine skin with Bloom number 300(Sigma-Aldrich, Sweden) was used to produce seven gels witha constant gelatin/water concentration and varying sugarconcentrations.

2.2. Sample preparation

Gelatin powder was dissolved in ultrapure water and left toswell for at least 60 min. At the same time, the desired amount ofsucrose was dissolved in ultrapure water. The gelatin solution washeated in a water bath at 70� 5 �C until the gelatin melted. Thesucrose solution was added, and the sample was re-heated. Thegelatin-sucrose solution was pipetted into small bakery tins(bottom diameter¼ 2 cm and height¼ 1.5 cm). Samples wereprepared as homogeneous or as layered (with five or seven layers).1 ml was pipetted for the five-layered samples and 0.7 ml waspipetted for the seven-layered samples for each layer. For thehomogenous samples, 5 ml was pipetted into the tins. Each layerwas approximately 2.2 mm thick in the five-layered samples and1.5 mm thick in the seven-layered. The samples were storedrefrigerated during and after preparation. Sensory testing ofsamples was performed within 3 days from preparation and thesamples were, on the testing day, left in room temperature fortemperature equilibration for about 4 hours prior to testing.Samples for rheological measurements in plate-plate geometry

were prepared in larger tins (diameter¼ 5 cm). For the kineticmeasurements, the gelatin solutions were poured directly into therheometer cup. Samples for texture analyzer profiling were gelledin 50 ml plastic beakers and left to gel in refrigerator. Two or threedroplets of red or yellow household caramel colouring were addedbefore gelling for a visual observation of diffusion. For the samplesused in the FRAP measurements, 50 ppm Na2-Fluorescein wasadded to the gelatin-sucrose solutions before they were pipettedinto the tins.

2.3. Sample composition

Seven samples were prepared as layered (with five or sevenlayers) or as homogeneous samples. For the layered gels, one layerat a time was gelled on top of the other(s). The homogeneoussamples were prepared as whole samples that were left to gel ina refrigerator (þ4–8 �C). The gelatin/water concentration was 5%(w/w) in each layer and in the homogeneous samples. The sugarconcentrations were 0, 9, 15 or 22.5% (w/w) in the homogeneoussamples, and the mean total sugar concentration was 9% (w/w) inthe layered gels. The sugar concentrations in the homogeneoussamples were similar to the concentrations in the single layers. Thehomogeneous samples were called H_0, H_9, H_15 and H_22.5(number¼ sugar conc.) and the layered samples where called LS_5,LD_5, and LD_7; LS¼ same layers, LD¼ different layers, and 5 and 7indicate the number of layers. The seven-layered samples hadlayers with 9% sugar on the outsides because in those cases theoutermost sugar concentration was the same as in the homoge-neous sample (H_9) and in the layered sample with five similarlayers (LS_5) (Fig. 1).

2.4. Rheological measurements

Gelation and melting kinetics of the samples without (H_0) andwith 22.5% sugar (H_22.5) were measured in a Stresstech rheometer(Reologica Instruments, Lund, Sweden) with stress controlledoscillation in a cup and bob geometry with a volume of 25 ml. Thehot sample was poured into the cup that was temperature condi-tioned to 50 �C, the bob was lowered, and the surface was coveredwith a lid to avoid evaporation and drying. The temperature wasslowly decreased (1 �C/min) to 20 �C. This temperature was keptconstant for at least 120 min, and the gelation process could befollowed. The temperature was then again raised to 50 �C (1 �C/min)and the melting was followed. The frequency was 1 Hz and the stress10 Pa. Measurements were made at least in duplicate.

The small deformation rheological measurements were per-formed on the single layers (w0.7 ml sample) at room temperaturein a Stresstech rheometer (Reologica Instruments, Lund, Sweden)with stress controlled oscillation in plate-plate geometry witha diameter of 30 mm. The samples were gelled in larger tins (w5 cmdiameter) the day before measurements and stored cold over night.On the measuring day, samples were temperature equilibrated inroom temperature and, just before measurements, circular discswere punched out. A stress-sweep, with stress running from 0.02 to500 Pa, at 1 Hz was first made to detect the linear viscoelastic region.A mechanical spectrum of the storage modulus (G0) and the lossmodulus (G00) was then measured in the linear viscoelastic region.The frequency was increased from 0.1 to 2 Hz at a constant stress of50 Pa and a constant temperature of 20 �C. Measurements weremade in triplicate. Large deformations were measured in a TA-XT 2iTexture Analyzer (Stable Micro Systems, Surrey, U.K.) with 75%deformation, and the tests were performed with a Ø 100 mm plate.Measurements were carried out on room tempered samples. Thecrosshead speed was 0.5 mm/s and the trigger force was 5 kg.

15%

9%

22.5%

H_9 LS_5 LD_5 LD_7

H_0 H_15 H_22.5

0%

Fig. 1. Sample structures and sugar distributions. Gel names are given above each sample, and the colouring indicates the sugar concentration; the more sugar, thedarker the colour.

K. Holm et al. / Food Hydrocolloids 23 (2009) 2388–23932390

Sample height was 35.7�2.73 mm (st. dev.) and diameter was30 mm. Measurements were made in triplicate.

2.5. FRAP measurements

To determine diffusion within the gels, fluorescence recoveryafter photobleaching (FRAP) experiments were performed witha confocal laser scanning microscope (CLSM) Leica TCS SP2 (LeicaMicrosystems Heidelberg GmbH, Germany). Thin slices of the gelswere used for measurements of diffusion in the x/y plane. Spotswith Ø (ROI)¼ 30 or 50 mm were bleached, and 50–125 imageswere then taken every 0.5 s to follow the fluorescence recovery.From the recovery data, diffusion constants in the gels werecalculated with the bleached disc model with a most likelihoodpixel based evaluation (Jonasson, Loren, Olofsson, Nyden, &Rudemo, 2008) according to equations (1) and (2). Measurementswere made at least in duplicate.

Fick’s law:

vCvt¼ D

1r

vCvtþ v2C

vr2

!(1)

D¼Diffusion constant (m2/s), C¼ concentration (mol/m3),r¼ radius (m).

Cðr; tÞ ¼ 12Dt

exp�� r2

4Dt

�ZN0

uC0ðuÞI0� ru

2Dt

�exp

�� u2

4Dt

�du

(2)

D¼Diffusion constant (m2/s), C0¼ concentration at t¼ 0(mol/m3), I0¼ Bessel function of order zero.

2.6. Sensory analysis

The sensory analysis was made in two separate experiments.Samples were evaluated by a trained analytical panel (SIK AB,Sweden) consisting of six and five persons respectively. Thesepersons were selected and trained according to ISO 8586-1993 andthe evaluations were made in a sensory laboratory equipped

according to ISO 8589-1988. Samples were cut from the tins, liftedup and put on spoons. The panellists were told to lift the samplefrom the spoon and put it on the tongue in the same direction as itwas placed on the spoon, i.e. with the layers in horizontal position.Water, wafers/bread or cucumber slices were used to rinse themouth and palate between gel samples. Scores were entereddirectly into computers (FIZZ, version 2.31E, Biosystemes, France).

2.7. Descriptive sensory analysis

2.7.1. Experiment IThe first sensory experiment was preceded by three training

sessions during which the six panellists developed an attribute list,which they practiced during the training sessions. The panellistswere trained in how to evaluate the selected taste, texture andbreakdown attributes of the gels. They were also trained in the useof the 100-unit continuous line scale, anchored at intensity 10(labelled ‘‘low’’) and at intensity 90 (labelled ‘‘high’’). The anchorpoints serve as guides to the panellists in the use of the scale. Thesamples were served at room temperature in random orderaccording to a Latin square design and evaluated in triplicate. ALatin square design serving order was used since it gives control ofthe variation in the factors, i.e. gels and panellists. With this servingorder all panellists tested all gels, but in different order. The sweettaste and gel hardness when pressing the gel between tongue andpalate were evaluated directly after the gel was put in the mouth.The samples were slightly chewed and the sweetness was assessafter three chews (¼15 s). The chewing was interrupted, and thesample was then only moved around in the mouth, not chewed.Sweetness was further assessed at times t¼ 30, 45 and 60 s. Att¼ 30 s, the separation of the pieces was also evaluated, and att¼ 45 s, the frothing (enhanced saliva production) was evaluated.At 60 s, the sample was swallowed or spitted out. The sweetafter-taste was evaluated at t¼ 75 s.

2.7.2. Experiment IIThe sugar concentration range was large in experiment I

(ranging from 0% to 22.5%), and a second analysis was made withonly 9% sugar samples. The whole scale range could then be used

K. Holm et al. / Food Hydrocolloids 23 (2009) 2388–2393 2391

for only these samples. The panel was the same as in experiment I,except for one panellist who could not participate; thus only onetraining session was needed. In this experiment, only samples with9% sugar were evaluated for their sweetness intensities at the sametime points as in experiment I. The panellists were instructed totreat and evaluate the gels in an identical way as in experiment I butonly to evaluate sweetness. Samples were served at roomtemperature in random order according to a Latin square designand evaluated in triplicate.

2.8. Evaluation

Two-way ANOVA was performed on sensory data, with samplesand panellists as fixed factors. Turkey’s multiple comparison testsfor experiment I and pair wise testing for experiment II were per-formed for all attributes and samples using SYSTAT (version 10.0,SPSS Inc., Chicago). In the Turkey’s multiple comparison tests, meanvalues for all samples are compared simultaneously and significancein all comparisons are needed for significant results from the test.

The performance of the panellists was evaluated using Pan-elCheck (version 1.2.1, Matforsk, Norway). The individual panellistswere tested for their ability to differentiate between samples andfor their ability to replicate their assessments.

3. Results and discussion

3.1. Rheology

A temperature ramp was used to follow gel formation andmelting of gelatin gels with different amounts of sugar. The gelationand melting behaviour did not differ between the sugar-free (H_0)and high-sugar (H_22.5) samples and Fig. 2 shows a typical curve ofthe changes in G0 and phase angle during gel formation and gelmelting. The onset of gelation and melting were measured at highsensitivity and no differences in the gelation or melting tempera-ture were found for different sugar concentrations. This impliesthat there is no effect of sugar on the conformational changesleading to gelation or any phase separation effects even at thehighest sugar concentration used in this study. Such observationshave been reported at sugar concentrations above 30% (Kasapis &Al-Marhoobi, 2003). All samples were in the gel state at tempera-tures around 25 �C. The melting was very rapid and the transitionfrom gel to liquid was completed at a similar temperature (w38 �C)for all samples. The continued small increase in G0 for time points>200 min was not believed to have any affect on the sensory

G´ (P

a)

Time (minutes)

Ph

as

e a

ng

le

, T

em

pe

ra

tu

re

(°C

)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 17 40 90 140 190 240 277 2930

10

20

30

40

50

60

70

80

90

100

Fig. 2. Gelation and melting kinetics for a 5% (w/w) gelatin gel with no sugar (H_0).A: G0 , dotted line: temperature and �: phase angle. G0 are plotted against the first yaxis; phase angle and temperature are plotted against the second y axis.

texture evaluation, since human sensibility for differences ininstrumental texture for such G0 values is probably not goodenough for sensing the difference (Chanasattru, Corradini, & Peleg,2002; Lawless & Heymann, 1998).

Viscoelastic measurements showed that the gels with 0%, 9%and 15% had similar G0 values at 1 Hz, which was an indication ofsimilar gel network structures. The G00 values were small, for thesesamples, i.e. the gels were highly elastic. The viscoelasticmeasurements were preceded by a stress-sweep indicating that, atf¼ 1 Hz and stress¼ 50 Pa, the material was within the viscoelasticregion. G0 and G00 values for all samples are shown in Fig. 3. Weworked with a constant gelatin/water concentration as a way tomaintain the rheology also in the case when sugar was added, andthis was successful up to at least 15% sugar. This approach isdifferent to most other studies that report work where a constanttotal gelatin concentration have been used, and the gels’ strengthswere then shown to increase with sugar addition (Al-Marhoobi &Kasapis, 2005), plausibly owing to increased gelatin/waterconcentrations.

The large deformation compression test showed that thesamples with 0% and 22.5% sugar behaved very similar for defor-mations up to 50%, and the modulus was slightly lower for thesugar containing sample (Fig. 4). For larger deformations, the high-sugar samples required higher forces, which may be related to themore viscous water phase in these samples.

3.2. Diffusion

By colouring the layers differently during build-up of the layeredgels, a visual observation proved that no diffusion of colouroccurred between the layers. Information about the diffusion in thegels was provided by the FRAP measurements. The fluorescent Na2-Fluorescein was in the same size range as sucrose (376 vs. 342 Da),and thus the calculated diffusion constants for this molecule weresupposed to be similar to those for sucrose. The diffusion constantsdecreased linearly (p< 0.05) with increasing sugar concentration(values for D: H_0¼167, H_9¼131, H_15¼108 andH_22.5¼75 mm2/s respectively). The decrease is probably a resultof increasing viscosity in the water phase as the sugar concentra-tion increases; at 20 �C the viscosity is about twice as high for 22.5%sugar in water as compared to pure water (Mageean, Kristott, &Jones, 1991). The diffusion constants did not vary with ROI (regionof interest, i.e. Ø of the bleached spot), and mean values werecalculated from all measurements, independent of ROI value. Thelow diffusion in all gels indicates that samples retained their sugar

Sample

G´, G

´´ (P

a)

0

500

1000

1500

2000

2500

H_0 H_9 H_15 H_22.5

a, ba

a, b

b

Fig. 3. G0 (grey) and G00 (black) for the single gel layers. Mean values are calculatedfrom three replicates. Different superscripts a–b above bars indicate significantdifferences (p< 0.05) between samples.

Deformation (%)

Fo

rce (N

)

0

5

10

15

20

25

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Fig. 4. Curves from compression tests of gelatin gels with 0% sugar (-) and 22.5%sugar (:). Mean values are calculated from three replicates.

K. Holm et al. / Food Hydrocolloids 23 (2009) 2388–23932392

distributions over short term storage. For long term storage,however, the sugar distribution will probably level out, andtherefore, in these cases, a physical barrier, e.g. acetem, may be analternative.

3.3. Sensory perception

The sensory perceptions of sweetness at different time points,hardness of the gels, separation of pieces during breakdown andfrothing (enhanced saliva production) for all layered and homo-geneous samples (Experiment I) are given in Table 1.

3.3.1. SweetnessThe sweetness intensity in the gels was higher in those with

higher sugar concentrations (p< 0.05) at all time points (Table 1),which was according to expectations, and it also proved the reli-ability of the panel, i.e. they could distinguish between sampleswith different sugar concentrations. The reliability was also evidentas low p values and MSE values from the ANOVA calculations inPanelCheck (p< 0.5; MSE< 250) (Tomic, Nilsen, Martens, & Naes,2007). There was a tendency toward higher sweetness in LD_7compared to H_9, even though the total sugar concentration wasthe same in these samples. However, when comparing all samples,the sugar concentration range (0–22.5%) was probably too large fora possible discrimination between samples with 9% sugar. A sepa-rate experiment was thus undertaken in order to compare the 9%samples, and the panel could then use the whole scale for onlythese samples.

The results of sensory experiment II are shown in Fig. 5. Thesample with seven different layers (LD_7) was perceived as sweeter(p< 0.05) than the homogeneous sample (H_9) at t¼ 0, 15 and 30 sand than LD_5 at t¼ 0 and 15 s. At all other time points, LD_7

Table 1Sensory scores for all samples and attributes in experiment I. Different superscripts a–d i

Sample Sweet t¼ 0 s Sweet t¼ 15 s Sweet t¼ 30 s Sweet t¼ 45 s

H_0 1.22a 1.17a 0.89a 1.00a

H_9 11.33b 21.94b 29.39b 34.28b

LS_5 10.56b 19.94b 27.56b 33.00b

LD_5 12.28b 20.78b 35.61b 40.17b

LD_7 13.78b 24.17b 35.39b.c 40.06b

H_15 20.56c 35.28c 46.44c 51.94c

H_22.5 28.22d 45.44c 55.56c 60.67c

tended to be perceived as the sweetest sample. LS_5 and LD_5 wereintermediate in sweetness intensities, which could probably berelated to their structures, being between H_9 and LD_7; they werelayered, but with smaller differences in sugar concentrationsthroughout the structure as compared to LD_7.

The results show the possibility of increasing the perception ofsweetness by distributing sugar in a structure. It is plausible that,when eating and chewing these gels, the receptors initially metdifferent amounts of sugar, which gave higher sweetness intensi-ties for the samples with sugar-rich layers. As the structures brokedown, the sugar distribution evened out; all samples got the samesugar concentration and the differences disappeared.

3.3.2. Texture and breakdown behaviourThe layered samples (LS_5, LD_5, and LD_7) were built of indi-

vidual layers where most of the layers were similar in rheology, andthese samples were also perceived as equally hard (Table 1). For thehomogenous samples, hardness decreased as the sugar concen-tration increased, and H_0 was perceived as 1.3 times harder thanH_22.5 (p< 0.05). These gels also differed in G0 (p< 0.10). All gelshad similar gelatin/water concentration, but the absolute gelatinconcentration in the samples varied due to their varying sugarconcentrations, and the total gelatin concentration ranged from3.8% (w/w) in H_22.5 to 5% (w/w) in H_0. One possibility is thatH_22.5 was perceived as less hard as compared to H_0 due to thelower total gelatin concentration, and plausibly owing to the lowerG0 value. However, there were no significant differences inperceived hardness for H_9 and H_22.5 although these samplesalso significantly differed in G0.

The breakdown behaviour varied with sugar concentration; thesugarless sample fell into large separated pieces and the smallerpieces from the ones with much sugar were in a ‘‘sludge’’, whichresulted in higher scores for the ‘‘separation of pieces’’ property forthe sugar-free sample (Table 1). The ‘‘sludge’’ formation is a result ofsample fracture in high-sugar samples, and could probably berelated to the higher viscosities in the water phase. For the sugar-free sample, the gelatin melted as no sugar could form any sludge.The sludge formation probably influence the sweetness perceptionas samples with more sludge tended to stay longer in mouth. AsFig. 4 indicated, there were differences in breakdown behaviourbetween the sugarless sample and the sample with 22.5% sugar,which may explain the differences in sensory perceptions of thebreakdown and pieces.

The frothing was evaluated after 45 s, and this property alsoseemed to follow sugar concentration (Table 1), which was obviousas a significantly lower (p< 0.05) frothing in the sugar-free samplecompared to all others, and a significantly higher (p< 0.05) frothingin H_22.5 compared to the others, except for H_15. Consequently, itwas expected that H_9 and LS_5 would have the same frothingproperties as they had similar sugar contents and sugar distribu-tions. However, the frothing was lower in LS_5, so the layers musthave affected this property and caused the differences. For LD_5

n a column indicate significant differences between these samples.

Sweet t¼ 60 s Sweet t¼ 75 s Hardness Separationof pieces

Frothing

1.11a 1.78a 66.89a 54.22a 33.56a

38.50b 28.72b 59.78a.b 54.44a 52.50b

34.44b 25.56b 60.11a.b 50.94a 50.17b

40.33b 30.61b.c 57.39a.b 47.39a 55.39b

41.06b 29.78b.c 61.78a.b 50.94a 50.00b

54.11c 38.78c 57.11a.b 48.78a 58.39b.c

61.33c 49.61d 52.44b 44.11a 66.11c

0

10

20

30

40

50

60

0 15 30 45 60 75Time (seconds)

Sw

eetn

ess in

ten

sity

Melting in mouth

3 chews

Swallow/spit out

H_9

LD_5

LS_5

LD_7

Fig. 5. Sweetness intensities from experiment II for samples with a total mean sugarconcentration of 9%. The different eating occasions are indicated along the time scale.Black (�): LD_7, Light grey solid ( ): LS_5, Light grey dotted ( ): LD_5, Dark grey ( ):H_9.

K. Holm et al. / Food Hydrocolloids 23 (2009) 2388–2393 2393

and LD_7, the frothing was probably a mixture of frothing behav-iours in the different layers within the structures. The frothing wasprobably a result of enhanced saliva production due to sugarcontent and sample time in mouth. At a ‘‘normal’’ eating behaviourthe sample would probably not have been kept in the mouth for60 s, which affected the saliva production, especially for the high-sugar sample as the sugarless sample tended to melt away.

The breakdown behaviour and frothing were reversely relatedto each other and to sugar concentration; samples with more sugarproduced more froth and had less separation between the piecesand the reverse.

4. Conclusion

Our results demonstrate the possibility of producing layeredgelatin gels with varying sugar concentrations throughout thestructure and with different sweetness intensities. The seven-layered sample (LD_7) was perceived as being sweeter than thehomogeneous sample (H_9), although they had the same totalsugar concentration but different sugar distributions. The highersweetness intensity in the seven-layered sample was probablybecause more sugar met the receptors at biting through this gel. It isplausible to believe from our results that gels with the sugarunevenly distributed can give similar sweetness as a homogenoussample, but with a lower sugar concentration.

All layered gels had similar hardness owing to their similarrheology in most of the single layers. The two 22.5% sugar layerswith lower G0 values in the seven-layered sample were probablynot different enough compared to the others to induce any sensorydifferences of hardness. The homogeneous samples with 15% and22.5% sugar were perceived as less hard than the sugarless sample,probably because of the lower total gelatin concentration in thesegels. Breakdown behaviour varied with sugar concentration; thesugarless sample fell into large, separated pieces in contrast to the

high-sugar samples, which fell into smaller pieces kept together ina ‘‘sludge’’, owing to the increased viscosities of the water phases inthese gels. The diffusion within the single layers indicates that noshort term levelling out of sugar concentration is likely to occur.

Acknowledgements

We want to thank Nordic Sugar AB and the Knowledge Foun-dation, through its research school YPK, for financial support. LarsBo Jørgensen, Kerstin Pehrson and Bertil Håkansson are gratefullyacknowledged for their fruitful discussions throughout the project.Ingela Gangby is thanked for her help during the sensory analyses.Joel Hagman and Niklas Loren are thanked for the FRAP measure-ments and for sharing their knowledge in this field.

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