Factors affecting the perception of creaminess of oil-in-water emulsions

Mahmood Akhtar, Juliane Stenzel, Brent S. Murray, Eric Dickinson*

Procter Department of Food Science, University of Leeds, Leeds LS2 9JT, UK

Abstract

Rheological properties and particle size distributions of butter fat-in-water emulsions stabilized by sodium caseinate (2–4 wt%) have been

investigated in relation to the texture descriptors ‘taste’, ‘thickness’ and ‘creaminess’. The effects of oil droplet size (0.5 and 2 mm), oil

volume fraction (5–20 vol%), and the addition of low-methoxy pectin or xanthan on texture perception have been evaluated at various

concentrations of the hydrocolloids (0.03–1 wt%). Particular sets of conditions were chosen so that the samples had the same apparent

viscosities at high shear-rate (50 sK1).

Sensory panel results show that the perception of all three descriptors was significantly influenced by the rheology and the fat content, with

higher ratings of all three descriptors scored for samples with higher viscosity and higher volume fraction. Discrimination between 5 and

20 vol% oil samples was stronger in the more viscous samples. Creaminess perception appeared to be more enhanced by a higher viscosity

than by a higher volume fraction of oil. Some correlations between the different texture descriptors and the shear-thinning rheology of the

samples were detected. Changing the oil droplet size from 0.5 to 2 mm had no significant influence on the perceived perception of taste,

thickness and creaminess.

q 2004 Elsevier Ltd. All rights reserved.

Keywords: Oil-in-water emulsions; Creaminess; Droplet-size distribution; Butter fat content; Pectin; Xanthan; Shear-thinning

1. Introduction

Creaminess is related to a pleasant sensation on eating. It

is associated with indicators of richness and high quality of

food products, especially those containing fat. In the

reduction of the fat content of food products, it is considered

a challenge to mimic the rheological effects of the fat

through the use of fat-replacing systems (Jones, 1996). With

the wide range of hydrocolloids, fat mimetics and texture

modifiers currently available, this approach is in principle a

relatively easy route. However, the matter of rheological

matching cannot be viewed in isolation, as it needs to be

related to the perceived sensory characteristics of a product,

in particular its creaminess.

Many of the sensory attributes of food emulsions—such

as creaminess, smoothness and sliminess—are often

difficult to characterize, but are probably related in some

way to their rheological properties. Food emulsions

0268-005X/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.foodhyd.2004.10.017

* Corresponding author. Tel.: C44 113 233 2956; fax: C44 113 233

2982.

E-mail address: e.dickinson@leeds.ac.uk (E. Dickinson).

generally exhibit non-Newtonian viscoelastic behaviour

and measurement of viscoelastic properties has for a long

time been a major area of research (Atkin & Sherman,

1980). Oral viscosity plays an important role in texture

perception of fluids and semi-solid foods. Perceived

‘thickness’ has been one of the most extensively investi-

gated textural attributes in fluids and beverages. A number

of attempts have been made to develop correlations between

sensory thickness and rheological properties and to

determine the shear-rates acting in the mouth in order to

relate thickness to the non-Newtonian shear-thinning

behaviour of foods (Cutler, Morris, & Taylor, 1983; de

Wijk, van Gemert, Marjolein, Terpstra, & Wilkinson, 2003;

Kokini, Poole, Mason, Miller, & Stier, 1984).

In a study where a thickening agent was used to increase

the viscosity of dairy samples of varying fat contents (Mela,

1988), only the sample with the highest fat content was

perceived equivalent to heavy cream (38% in fat content).

As dairy creams are oil-in-water emulsions, any influence

that the fat content has on texture perception should be

related to the physical properties of the fat globules. Some

researchers have shown (Daget, Joerg, & Bourne, 1987;

Food Hydrocolloids 19 (2005) 521–526

www.elsevier.com/locate/foodhyd

M. Akhtar et al. / Food Hydrocolloids 19 (2005) 521–526522

Wood, 1974) that ‘creaminess’ is sensed only if a certain

viscosity threshold is met. Despite extensive research in this

area (Drewnowski, 1987; Jowitt, 1974; Kokini & Cussler

1983; Kokini et al., 1984; Richardson-Harman et al., 2000;

Malone, Appelqvist, & Norton, 2003), the most appropriate

choice of terminology and sensory attributes to describe the

textural contributions of fat in food products is still to be

fully resolved.

In a review of this subject, Kokini (1987) attempted to

relate liquid and semi-solid texture to the rheological and

frictional properties. Creaminess was supposed to depend

largely on smoothness and thickness (Kokini et al., 1984). In

turn, thickness and smoothness were separately considered

to be related to the viscous and frictional properties

experienced in the mouth, allowing the identification of

measurable physical properties to predict perceived texture

and mouthfeel.

Many of the food systems exhibiting ‘creamy’ charac-

teristics are oil-in-water emulsions, and so these particular

systems have received most attention. Mela, Langley, and

Martin (1994) reported the results of a sensory panel where

the perception of fat in model oil-in-water emulsions with

different fat contents increased with increasing viscosity at a

shear-rate of 48 sK1. In addition to the basic rheological

characteristics of oil-in-water food emulsions, the import-

ance of the size and number of fat droplets has also received

some attention (Richardson, Booth, & Stanley, 1993). The

results of Mela et al. (1994) showed no apparent pattern in

terms of oil droplet size as affected by fat content in

emulsions containing 0–48% fat. Richardson and Booth

(1993) investigated further the effect of viscosity, globule-

size distribution and average inter-globule distance on the

perceived creamy texture of milks and creams. It was

suggested that a wide variation in globule size might

contribute to a lack of smoothness in dairy emulsions. By

varying the amount and dispersion of fat independently of

the viscosity of the emulsion, Richardson and Booth (1993)

concluded that there was support for the more general

hypothesis that emulsified fat contributes something to

creaminess in addition to its effect on viscosity. Another

more complicated factor that can potentially influence the

rheological behaviour of emulsions and their sensory

perception in the mouth is the state of aggregation of the

droplets (Depree & Savage, 2001; Tornberg, Carlier,

Willers, & Muhrbeck, 2005; van Vliet, 1988).

Despite extensive research, however, it is still not fully

understood what exactly causes the perception of creami-

ness. This present study investigates the influence of fat

content, rheology and microstructure (particle size) on the

perception of taste, thickness and creaminess in model

butter fat-in-water emulsions. In contrast to many previous

studies, particular attention is given here to the careful

control of the particle size distribution and the shear-rate-

dependent rheology of the emulsion samples. For the

experiments reported in this paper, the system conditions

are adjusted to avoid aggregation of the droplets:

the concentration of protein (sodium caseinate) is above

that giving bridging flocculation, but below that giving

depletion flocculation (Dickinson & Golding, 1997), whilst

the concentration of xanthan is above that giving extensive

serum separation by depletion (Cao, Dickinson & Wedlock,

1990; Dickinson, 2003). The overall aim of the project is to

investigate the main physico-chemical factors affecting the

perception of creaminess of these model oil-in-water

emulsions, and also to explore the general relationship

between rheological and perceived sensory characteristics

of dairy emulsions.

2. Materials and methods

2.1. Materials

Commercial sodium caseinate (5 wt% moisture,

0.04 wt% calcium) was a gift from DMV International

(Veghel, Netherlands). This was a spray-dried, food-grade

product with a minimum of 91% dry protein, a maximum

moisture content of 5.0%, and less than 4.0% fat and ash.

Butter fat was provided by the Hannah Research Institute

(Ayr, UK). Two commercial biopolymers, low-methoxyl

pectin (DE 31) and xanthan gum (food grade), were

purchased from CP Kelco (UK).

2.2. Emulsion preparation and droplet size measurement

Sodium caseinate was dissolved in drinking water at

room temperature. The aqueous phase (4 wt% protein, pH

6.8) and the butter fat were heated in a water bath at 50 8C

for 40 min. Butter fat-in-water emulsions (30 vol%,

2.8 wt% sodium caseinate) were prepared at 50 8C using a

laboratory-scale jet homogenizer (Burgaud, Dickinson, &

Nelson, 1990) working at the operational pressure of

350 bar. Emulsions were diluted with drinking water in

order to reduce the fat level to 5 or 20 vol% in the final

emulsion. The hydrocolloid (pectin or xanthan) was care-

fully dissolved in distilled water to a solution of known

concentration. Resulting solutions were then mixed with the

emulsions by gentle stirring in order to adjust the viscosity.

Emulsion droplet-size distributions were measured using

a Malvern Mastersizer MS2000 laser light-scattering

analyser with absorption parameter value of 0.001 and

refractive index ratio of 1.46. The average droplet size was

characterized by the mean diameter d43, defined by

d43 Z Sinid4i =Sinid

3i ;

where ni is the number of droplets of diameter di. The d43

value was used to monitor changes in the droplet-size

distribution of freshly made emulsions on storage. Creaming

stability was assessed visually by determining the time-

dependent thickness of cream and serum layers in emulsions

stored at 6 8C.

Fig. 1. Viscosity profiles of 20 vol% butter fat emulsions with varying

concentrations of hydrocolloids added: (a) pectin; 0.2% (6), 0.4% (C),

0.8% (B); (b) xanthan; 0.03% (6), 0.05% (C), 0.1% (,). The arrow

indicates the apparent viscosities at a shear-rate of 50 sK1.

M. Akhtar et al. / Food Hydrocolloids 19 (2005) 521–526 523

2.3. Rheological measurement

Steady-state viscosities of butter fat-in-water emulsions

were determined using a Bohlin rheometer (CVO) with C25

cup and bob geometry. The sample was poured into the

rheometer cell, surrounded by a temperature controlled

vessel, and allowed to equilibrate at 20 8C for 10 min prior to

the measurement. Apparent viscosity was measured at shear-

rates of 0.1–200 sK1 using continuous shear with 30 s delay

time and 30 s integration time at constant temperature of

20 8C.

2.4. Sensory panel assessment

Butter fat-in-water emulsions of known particle size

distribution and viscosity were assessed by an untrained

sensory panel comprising 14 assessors. Samples of dairy

emulsions were prepared one day prior to tasting, and were

stored at 5 8C prior to assessment by the panelists at 21 8C.

The samples were presented in a regulated presentation

sequence and coded with random numbers. The order of

samples presented to the panelists was also randomized

across sessions. Canned mixed fruit cocktail was given to the

panelists to eat between each tasting. Samples were assessed

in duplicate. Panel members were asked to rate perception of

‘taste’, ‘thickness’ and ‘creaminess’ on a scale of 1–10 where

10 corresponds to the highest rating. Emulsions were varied

in two factors: droplet size (d43 from 0.5 to 2.3 mm) and

apparent viscosity (from 8 to 50 mPa s) at a shear-rate of

50 sK1. The data were analysed by the Statgraphics (Sgwin)

program with multifactor categorical design (3 response

variables, 2 experimental factors, 2 levels for each factor).

3. Results and discussion

3.1. Rheological measurement

Flow properties are important determinants in the

sensory assessment of fluid and semi-solid foods (Stanley

& Taylor, 1993). This is because the viscosity-related

properties of liquid and semi-solid foods are assessed orally

by measuring their resistance to flow, the rate of flow over

the surface of the mechanoreceptors, and also by the amount

of force required to manipulate the fluid in the mouth

(Christensen & Casper, 1987).

We have attempted to evaluate the effect of viscosity on

the texture perception of our model dairy emulsions using

two hydrocolloids as thickening agents: low-methoxy pectin

(pectin) and xanthan gum (xanthan). The 30 vol% butter fat-

in-water emulsions (2.8 wt% sodium caseinate, mean droplet

size d43Z0.5 mm) were made as described above. The

emulsions were diluted with solutions of various concen-

trations of xanthan (0.03–0.1%) or pectin (0.2–0.8%) to raise

the viscosity of the continuous phase and also to reduce the

oil volume fraction to 5 and 20 vol%. All emulsion samples

were tested viscometrically at shear-rates of 0.1–200 sK1 at

20 8C. Viscosity profiles for the emulsions are shown in Fig. 1

for (a) pectin and (b) xanthan. Emulsions containing either

polymer show similar shear-thinning behaviour over the

shear-rate range tested. Increasing the content of hydro-

colloid increases the high-shear viscosity (50 sK1).

While both hydrocolloids show qualitatively similar

rheological properties, the concentration of hydrocolloid

required to raise the viscosity by the same factor is clearly

dependent on the type of biopolymer used. For example, a

much lower concentration of xanthan (0.03 wt%) was

required to raise the viscosity to the same level at a low

shear-rate (0.1 sK1) as obtained with 0.2 wt% pectin.

Emulsions containing 0.05 wt% xanthan or 0.4 wt% pectin

had the same low-shear-rate viscosity. Approximately

0.1 wt% xanthan was found to have the same effect as

0.8 wt% pectin in raising the apparent viscosity over the

whole shear-rate range. The viscosity values were fairly

reproducible, with an experimental error of G1 mPa s for

the low-shear viscosities.

3.2. Particle size distributions

Two different emulsions (d43Z0.56 mm and d43Z2.34 mm) were successfully made with well-defined particle

Fig. 2. (a) Droplet-size distributions of fine and coarse emulsions of 5 vol%

butter fat. (b) Viscosity profiles for fine and coarse emulsions with

viscosities adjusted by addition of hydrocolloid: filled symbols d43Z0.56 mm; open symbols d43Z2.34 mm.

Fig. 3. Effects of viscosity and oil droplet size on perceived (a) thickness

and (b) creaminess of emulsions made with 5 vol% butter fat: filled symbols

d43Z0.56 mm; open symbols: d43Z2.34 mm.

M. Akhtar et al. / Food Hydrocolloids 19 (2005) 521–526524

size distributions as shown in Fig. 2(a). The distributions

were monomodal with no evidence of flocculation. There

was no change in the average particle size measured when

these emulsions were diluted with drinking water to achieve

5 vol% butter fat levels in the final emulsion. The fine and

coarse emulsions were tested rheologically under similar

conditions. Table 1 shows the physical characteristics in

terms of the average droplet size and apparent viscosity (at a

shear-rate of 50 sK1) for the 5 and 20 vol% butter fat-in-

water emulsions. The values of the different droplet sizes

were chosen so that the ratio between the high and low

values of various parameters was approximately the same;

that is, the ratio between the coarse and fine droplet size is

the roughly same as for the 4:1 ratio of the high and low oil

volume fractions, and also roughly the same as for the ratio

of high-shear viscosities.

Table 1

Physical characteristics of butter fat-in-water emulsions

Oil volume

fraction

Average droplet

size d43 (mm)

Xanthan (wt%) Viscosity (mPa s)

at 50 sK1

0.05 0.56 0.03 10G1

0.05 0.56 0.15 46G4

0.05 2.34 0.03 9G1

0.05 2.34 0.15 46G4

0.20 0.51 0 10G1

0.20 0.51 0.11 54G6

0.20 1.92 0 10G1

0.20 1.92 0.11 55G5

The viscosity profiles for the fine and coarse emulsions

(0.56, 2.34 mm) as a function of shear-rate are shown in

Fig. 2(b). The data show that varying the droplet size of the

emulsions in this range has no significant effect on the

emulsion rheology.

On the basis of visual observations in small sample

containers, the emulsion samples were stable with respect to

creaming and serum separation over the timescales of the

physico-chemical measurements and the sensory tests.

3.3. Sensory panel assessment: viscosity versus droplet size

Mean values of perceived thickness and creaminess as

function of measured viscosity (at 50 sK1) and oil droplet

size are shown in Fig. 3. The analysis of the variance

presented in Table 2 shows significant results (i.e. P!0.05)

for two of the texture attributes: thickness and creaminess.

The panel results confirm that apparent viscosity is a strong

influence in consumer perception of both thickness

Table 2

Sets of P-values from the analysis of variance for the perceived

perception of taste, thickness and creaminess of 5 vol% butter fat-in-

water emulsions

Factors Attributes

Taste Thickness Creaminess

A: droplet size 0.8978 0.6825 0.5894

B: viscosity 0.3695 0.0000 0.0061

A/B interaction 0.8978 0.6825 0.7189

M. Akhtar et al. / Food Hydrocolloids 19 (2005) 521–526 525

and creaminess. In particular, the good correlation between

the rheological and the sensory results suggests that the

viscosity of the continuous phase was the dominating

attribute controlling the perceived creaminess. A similar

strong effect of emulsion flow behaviour has been reported

in the literature (Mela et al., 1994), where perceived

creaminess was considered to be strongly influenced by the

viscosity of the continuous phase.

The results in Table 2 show that the panelists were unable

to discriminate between emulsions of different mean droplet

size in the range 0.5–2.3 mm. The sensory analysis data are

therefore consistent with the instrumental data in Fig. 2(b),

indicating that the rheology is insensitive to the droplet-size

distribution. This may be consistent with evidence from the

literature (Tyle, 1993) which suggests that consumers are

only able to detect food particles at least as small as 5 mm.

Perception of the taste of our model dairy emulsions was

judged by the panel members to be ‘pleasant’ and to be

unaffected by the viscosity or the variation in oil droplet size.

The key finding from these experiments is that only the

viscosity of the continuous phase has a major influence on

the perceived textural characteristics of thickness and

creaminess, but not on taste.

3.4. Effect of the type of hydrocolloid

An attempt has been made to test whether the choice of

hydrocolloid affects the sensory perception of taste,

Fig. 4. Effect of hydrocolloid type on the perception of (a) thickness and (b)

creaminess of butter fat-in-water emulsions (22 vol%): filled symbols,

pectin (0.8 wt%); open symbols xanthan (0.1 wt%).

thickness and creaminess of the model emulsions

(22 vol% butter fat). Pectin at 0.8 wt% and xanthan at

0.1 wt% were used to raise the viscosity of the continuous

phase of the dairy emulsions to the same level at a shear-rate

of 50 sK1. The emulsions had an average droplet size of

d43Z0.54 mm. The sensory panel comprised 14 assessors,

and the samples were presented as described previously.

Mean values of thickness and creaminess as a function of

the viscosity and type of polymer are presented in Fig. 4.

Again, the results show that the perception of thickness and

creaminess increases with increase in the viscosity of the

continuous phase. However, these sensory data also show

that the perceived thickness and creaminess were not

sensitive to the type of hydrocolloid incorporated (at least

insofar as pectin and xanthan are concerned). Hence, it

appears that it is the viscosity that is important in relation to

perceived creaminess, and not the actual concentration of

the hydrocolloid, which is eight times higher in the case of

pectin.

3.5. Effect of oil volume fraction

Emulsions were made with two different butter fat levels:

5 and 20 vol%. Mean values of perceived thickness and

creaminess are shown in Fig. 5. The results show that the fat

content has a slightly positive effect on the perception of

thickness and creaminess for the high-viscosity samples

Fig. 5. Effect of fat content on perception of (a) thickness and (b)

creaminess of emulsions having different viscosities at 50 sK1: filled

symbols, 50 mPa s; open symbols, 8 mPa s.

M. Akhtar et al. / Food Hydrocolloids 19 (2005) 521–526526

(50 mPa s at 50 sK1). But for the low-viscosity emulsions

(8 mPa s at 50 sK1) the effect of fat content on the

perception of thickness and creaminess is negligible. This

data set again shows that the apparent viscosity is the most

significant factor in determining creaminess perception. Fat

content and oil droplet size were much less significant

factors. There was also little evidence of significant

interaction between these different variables in determining

overall creaminess.

4. Conclusions

We have investigated the factors affecting the perception

of taste, thickness and creaminess of model emulsions with

respect to viscosity, oil droplet size and oil volume fraction.

A simple emulsion system stabilized by sodium caseinate

appears to be a useful model for investigating these factors.

The apparent viscosity at a shear-rate of 50 sK1 was found

to have a very significant effect on perception of thickness

and creaminess. The fat content has a small, but significant

influence for high viscosity samples. No statistically

significant differences were found for emulsions of two

different mean droplet sizes (0.56 and 2.34 mm), but having

the same rheological behaviour. Also no perceived differ-

ences were found between emulsion samples of the same

viscosity and fat content adjusted with either pectin or

xanthan. Perception of the taste of these emulsions was

unaffected by both the oil droplet size and the fat content.

Acknowledgements

This project was supported by BBSRC grant 24D/15889.

The work forms part of a collaboration with Professor David

Booth, School of Psychology, University of Birmingham.

References

Atkin, G., & Sherman, P. (1980). Further applications of the modified gel

rigidity modulus apparatus. Journal of Texture Studies, 10, 253–259.

Burgaud, I., Dickinson, E., & Nelson, P. V. (1990). An improved high-

pressure homogenizer for making fine emulsions on a small scale.

International Journal of Food Science and Technology, 25, 39–46.

Cao, Y., Dickinson, E., & Wedlock, D. J. (1990). Creaming and

flocculation in emulsions containing polysaccharide. Food Hydrocol-

loids, 4, 185–195.

Christensen, C. M., & Casper, L. M. (1987). Oral and nonoral perception of

solution viscosity. Journal of Food Science, 52, 445–447.

Cutler, A. N., Morris, E. R., & Taylor, L. J. (1983). Oral perception of

viscosity in fluid foods and model systems. Journal of Texture Studies,

14, 377–395.

Daget, N., Joerg, M., & Bourne, M. (1987). Creamy perception in model

dessert creams. Journal of Texture Studies, 18, 367–388.

Depree, J. A., & Savage, G. P. (2001). Physical and flavour stability of

mayonnaise. Trends in Food Science and Technology, 12, 157–163.

de Wijk, R. A., van Gemert, L. J., Marjolein, P., Terpstra, E. J., &

Wilkinson, C. L. (2003). Texture of semi-solids; sensory and

instrumental measurements on vanilla custard desserts. Journal of

Food Quality and Preference, 14, 305–317.

Dickinson, E. (2003). Hydrocolloids at interfaces and the influence on the

properties of dispersed systems. Food Hydrocolloids, 17, 25–39.

Dickinson, E., & Golding, M. (1997). Depletion flocculation of emulsions

containing unadsorbed sodium caseinate. Food Hydrocolloids, 11,

13–18.

Drewnowski, A. (1987). Fats and food acceptance: sensory, hedonic and

attitudinal aspects. In J. Solms, D. A. Booth, R. M. Pangborn, & O.

Raunhardt (Eds.), Food acceptance and nutrition (pp. 189–204). New

York: Academic Press.

Jones, S. A. (1996). Physical, chemical and sensory aspects of fat

replacement. In S. Roller, & S. A. Jones (Eds.), Handbook of fat

replacers (pp. 2–12). Boca Raton: CRC Press.

Jowitt, R. (1974). The terminology of food texture. Journal of Texture

Studies, 5, 351–358.

Kokini, J. L. (1987). The physical basis of liquid food texture and texture–

taste interactions. Journal of Food Engineering, 6, 51–81.

Kokini, J. L., & Cussler, E. L. (1983). Predicting the texture of liquid and

melting semi-solid foods. Journal of Food Science, 48, 1221–1225.

Kokini, J. K., Poole, M., Mason, P., Miller, S., & Stier, E. F. (1984).

Identification of key textural attributes of fluids and semi-solid foods

using regression analysis. Journal of Food Science, 49, 47–51.

Malone, M. E., Appelqvist, I. A. M., & Norton, I. T. (2003). Oral behaviour

of food hydrocolloids and emulsions. Part 1. Lubrication and deposition

considerations. Food Hydrocolloids, 17, 763–773.

Mela, D. J. (1988). Sensory assessment of fat content in fluid dairy products.

Appetite, 10, 37–44.

Mela, D. J., Langley, K. R., & Martin, A. (1994). Sensory assessment of fat

content: effect of emulsion and subject characteristics. Appetite, 22, 67–

81.

Richardson, N. J., & Booth, D. A. (1993). Multiple physical patterns in

judgment of the creamy texture of milks and creams. Acta Psychology,

84, 93–101.

Richardson, N. J., Booth, D. A., & Stanley, N. L. (1993). Effect of

homogenisation and fat content on oral perception of low and high

viscosity model creams. Journal of Sensory Studies, 8, 133–143.

Richardson-Harman, N. J., Stevens, R., Walker, S., Gamble, J., Miller, M.,

Wong, M., & McPherson, A. (2000). Mapping consumer perceptions of

creaminess and liking for liquid dairy products. Food Quality and

Preference, 11, 239–246.

Stanley, N. I., & Taylor, L. J. (1993). Rheological basis of oral

characteristics of fluid and semi-solid foods: a review. Acta Psychology,

84, 79–92.

Tornberg, E., Carlier, N., Willers, E. P., & Muhrbeck, P. (2005). Sensory

perception of salad dressings with varying fat content, oil droplet size,

and degree of aggregation. In E. Dickinson (Ed.), Food colloids:

interactions, microstructure and processing (pp. 367–379). Cambridge:

Royal Society of Chemistry.

Tyle, P. (1993). Effect of size, shape and hardness of particles in suspension

on oral texture and palatability. Acta Psychology, 84, 111–118.

van Vliet, T. (1988). Rheological properties of filled gels—influence of

filler-matrix interaction. Colloid and Polymer Science, 266, 518–524.

Wood, F. W. (1974). An approach to understanding creaminess. Die Starke,

26, 127–130.