2Rheol - Choco Rheology 329

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3rd International Symposium on Food Rheology and Structure

329

EFFECTS OF DIFFERENT EMULSIFIERS ON RHEOLOGICAL ANDPHYSICAL PROPERTIES OF CHOCOLATE

Birgit Schantz, Lothar Linke, Harald Rohm

Institute of Food Technology and Bioprocess Engineering, Dresden University of Technology,

D-01062 Dresden, Germany

ABSTRACT

The influence of several commercially available emulsi-

fiers on the flow properties, crystallisation and solidifi-

cation behaviour as well as on the physical stability of

dark and whole milk chocolate was determined. The

investigations partly showed a pronounced influence on

viscosity and/or yield value of chocolate masses, de-

pending on the type of emulsifier and its concentration,

which was varied in a technological relevant range.

Besides some effects on the crystallisation behaviour,

the physical stability of filled chocolate was clearly in-

fluenced by the emulsifier in case of alcoholic aqueous

fillings, whereas fat-based fillings were hardly affected

by the emulsifier.

1 INTRODUCTION

Emulsifiers added to melted chocolate tend to

concentrate at the area between the liquid contin-uum (cacaobutter) and the solid phase, i.e., parti-

cles of sugar, cacao solids, and milk powder. Be-

cause of their special molecular structure and their

lipophilic and hydrophilic functional groups, they

are able to lower the interfacial tension between

these components, and are known to affect a

number of properties of the suspension, e.g.,

rheology, the sensitivity to moisture and temper-

ature, and tempering behaviour. Furthermore, the

addition of emulsifiers may presumably influenceproperties such as bloom, the stability against

fillings, and oxidisation [1, 2].

However, the main advantage of emulsifier appli-

cation in chocolate is the improvement of flow

parameters, thus allowing to minimise cacaobutter

addition and to reduce production costs. The

function of lecithin as the most commonly used

emulsifier in chocolate technology has been ex-

tensively studied. Since 1998, some more surface-

active components have been approved for the

use in chocolate by German legislation. The aim

of the current study was to compare the effects of

potential alternatives and standard lecithin on phy-

sical properties of fluid and solid chocolate prod-

ucts.

2 MATERIALS

A dark chocolate mass (D) containing 34 % fat

and a whole milk chocolate (WM) with 31 % fat

were manufactured without emulsifier addition.

Several types of surface-active substances from

different manufacturers were added to the base

masses. Apart from lecithin (L), we used ammon-

iumphosphatide (YN), polyglycerol polyricinoleate

(PGPR), sorbitan tristearate (STS) and mono- and

diglycerides (MD), which are all permitted in Ger-

many. Samples were prepared by adding a de-

fined amount of emulsifier to a fixed quantity of

base chocolate mass, followed by a defined man-

ual mixing procedure [3].

3 EXPERIMENTAL RESULTS

3.1 Determination of flow curves

It is well known that the addition of different types

and amounts of emulsifiers leads to chocolate

masses showing a wide spectrum of flow proper-

ties. Therefore, a method of measurement appli-

cable to all chocolate systems had to be devel-

oped.

Viscosity measurements were carried out at 40°Cwith a UM rheometer (PHYSICA Messtechnik

GmbH, Germany) in a controlled shear rate rota-

tion mode using a Z3 DIN concentric cylinder

measuring geometry. After 5 min of pre-shearing

at 200 s-1

and 150 s-1

for dark chocolate and

whole milk chocolate, respectively, shear rate was

reduced to 0.1 s-1

within 10 min in a logarithmic

ramp, and the corresponding flow curves were re-

corded.

Due to the largely different shapes of the flow cur-

ves, the calculation of equilibrium viscosity and

yield stress by a uniform mathematical model did




330

not lead to reasonable results. However, reliable

results require the equal handling of all data series

with a uniform modelling method. Therefore, addi-

tional data were collected during 1 min after the

pre-shearing period as well as during 1 min at the

minimum shear rate of 0.1 s-1

, thus allowing a

direct estimation of viscosity and yield stress. In

case of masses with a very high viscosity, yield

stress was determined from the bending point in

the flow curves.

Generally, both dark chocolate and whole milk

chocolate showed a similar qualitative response

with respect to type and concentration of the ad-

ded emulsifying agent. Quantitative differences

between D- and WM-systems, observed for visco-

sities and yield values, are obviously attributable to

the different fat contents and, hence, flow

properties of the emulsifier-free base masses.

Figure 1: Effects of selected emulsifiers on the viscosity

of dark chocolate. L, lecithin; YN, ammoniumphospha-

tide; PGPR, polyglycerol polyricinoleate; MD, mono-

and diglycerides; STS, sorbitan tristearate.

Figures 1 and 2 depict the rheological efficiency of

selected emulsifiers in dark chocolate mass. As

compared to melted chocolate without emulsifier,

the reduction of apparent viscosity was highest

after addition of lecithin and YN, followed by

PGPR. At an emulsifier concentration of 0.4 %,

which is most commonly used in chocolate tech-

nology, the relative reduction of viscosity was

approx. 40 % for emulsifiers L and YN, 30 % for PGPR and about 10 % for MD and STS. Again

based on a 0.4 % concentration level, the highest

reduction of yield stress appeared in masses

made by addition with PGPR (90 %), followed by L

and YN-masses (60 %), whereas STS and MD

showed only minor effects on the yield stress. In

case of deoiled lecithin with a higher relative

amount of surface-active groups, a significant

yield stress minimum was observed at an emulsi-

fier concentration of 0.2 % (results not shown).

Figure 2: Effects of selected emulsifiers on the yield

stress of dark chocolate. L, lecithin; YN, ammonium-

phosphatide; PGPR, polyglycerol polyricinoleate; MD,

mono- and diglycerides; STS, sorbitan tristearate.

3.2 Crystallisation

The process of pre-crystallisation and, consequen-

tly, the following solidification of chocolate is partly

shear-induced and, therefore, affected by the

rheological properties of the processed mass [4,

5]. Since emulsifiers heavily influence the flow

properties of melted chocolate, it is difficult to

distinguish between rheologically caused effects

and effects caused by the emulsifier as a

substance.

To answer the question whether the emulsifier

itself affects crystallisation, it is necessary to elim-

inate shear flow as a factor of influence. Conse-

quently, stationary pre-crystallisation with manual

torque adaption was applied by using a RHEO-

SYST 5000 (Coesfeld GmbH, Germany), defining

the torque profile during pre-crystallisation of leci-

thinated chocolate under fixed mixing and temper-

ature conditions as standard. The investigation

was carried out only with alternative emulsifiers(PGPR, YN) that proved to be rheological active at

a concentration of 0.4 %. Rotation speed for YN

0

1

2

3

4

Viscosity [Pa.s]

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Emulsifier concentration [%]

L

YN

PGPR

MD

STS

0

10

20

30

40

Yield Stress [Pa]

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Emulsifier concentration [%]

LYN

PGPR

MD

STS




331

and PGPR-chocolate pre-crystallisation was ap-

propriately changed to approach these torque pro-

files, allowing to compare seed-forming time and

complete crystallisation time.

In a second trial, the controlled-torque method

was applied to determine an optimum re-heating

temperature at the end of the pre-crystallisation

process. This temperature can be estimated by

taking samples of chocolate at several end tem-

peratures, and by visually assessing the solidified

product with respect to demoulding, appearance

and gloss. Based on visual inspection, the sam-

ples were classified in 5 groups:

• Strongly under-crystallised

• Under-crystallised

• Optimum

• Over-crystallised

• Strongly over-crystallised

Whereas only minor rotation speed corrections

were necessary for YN-chocolate, PGPR-masses

had to be crystallised with noticeable lower revolu-

tion as compared to standard L-masses. This is

attributable to the higher viscosity values of choco-

late made with PGPR, resulting in a higher torque

during mixing.

Figure 3 shows the seed-forming and crystallisa-

tion times of dark and whole milk chocolate prepa-red with different emulsifiers. PGPR-chocolate

tends towards faster seed-forming, and shorter

crystallisation times might be an indicator for en-

hanced susceptibility to over-crystallisation.

Figure 3: Seed-forming time and crystallisation time of

chocolate masses as affected by the emulsifier. L,lecithin; YN, ammoniumphosphatide; PGPR, polyglyce-

rol polyricinoleate.

This behaviour was confirmed by the results of the

second trial (Figure 4): higher re-heating tempera-

tures were required for PGPR-chocolate than for

lecithin masses to achieve optimum quality. This

tendency appears even in chocolates prepared

with an 0.2 % / 0.2 % mixture of lecithin and

PGPR. Consequently, the influence of the type of

emulsifier on the crystallisation behaviour of cho-

colate is clearly evident [6, 7].

Figure 4: Re-heating temperature of dark chocolate

(upper fgigure) and whole milk chocolate (lower figure).

L, lecithin; YN, ammoniumphosphatide; PGPR, polygly-

cerol polyricinoleate; L/PGPR, mixture of L and PGPR.

Classification of results: 1, strongly under-crystallised;

2, under-crystallised; 3, optimum; 3, over-crystallised,

5, stongly over-crystallised.

3.3 Physical shelf life

Among the reasons for the quality loss of filled

chocolate products during storage are interactions

at the interface between the chocolate cover and

the filling, presumably resulting in deterioration of

gloss, stability and taste. It is of high economical

interest to know whether emulsifiers are able to

improve the resistance of chocolate against the

fillings.

In our study, we used a standard brandy filling (65

% sugar content, 17,5 % ethanol) and sunflower oil as representative examples for an aqueous

alcoholic filling and a fat-based filling, respectively.

0

30

60

90

120

Time [min]

L YN PGPR L YN PGPR

Dark chocolate Whole milk chocolate

Seed-Forming

Crystallisation

L

YN

L/PGPR

PGPR

30 32 34 36 38

Re-heating temperature [°C]

L

YN

L/PGPR

PGPR

5

4

3

2

1




332

The experiments were performed with D and WM

chocolate masses with 0.4 % of the emulsifiers L,

YN, PGPR, and a L/PGPR-mixture (0.2 % each).

The reverse model method was used to achieve

reliable results within a short period of time [8].

Cylindrical samples of chocolate were placed in

beakers containing the filling material and stored

at 26 °C (brandy filling) or 18 °C (sunflower oil).

The firmness of the chocolate cylinders was

measured in intervals of 7 days by means of a

penetration method, using a 27° stainless steel

cone with a total mass of 22 g.

Figure 5: Structure loss of chocolate in alcoholic fillings

as affected by emulsifier type and storage time. Closed

symbols, dark chocolate; open symbols, whole milk

chocolate. L, lecithin; YN, ammoniumphosphatide;

PGPR, polyglycerol polyricinoleate; L/PGPR, mixture of

L and PGPR.

It is obvious from Figure 5 that, for both dark

chocolate and whole milk chocolate, the type of

emulsifier largely determines the stability againstalcoholic fillings. Evidently, masses made with

addition of lecithin, showing a more polar molecu-

lar structure than YN and PGPR, are less resistant

to diffusion of aqueous filling compounds into cho-

colate, consequently showing an enhanced stabi-

lity loss than masses made by addition of synthetic

emulsifiers such as YN and PGPR. Reduced

stability was also observed when using lecithin in

combination with PGPR. Additionally, milk

components significantly decreased stability

losses during storage.

Figure 6: Structure loss of chocolate in sunflower oil as

affected by emulsifier type and storage time. Closedsymbols, dark chocolate; open symbols, whole milk

chocolate. L, lecithin; YN, ammoniumphosphatide;

PGPR, polyglycerol polyricinoleate; L/PGPR, mixture of

L and PGPR.

Fat based fillings interact with the covering choco-

late obviously by another principle as the contin-

uous cacaobutter phase is affected rather than

sugar, cacao solids, and milk particles. Figure 6

depicts structure loss of dark and whole milk cho-

colate as a function of storage time in sunflower

oil. Obviously, neither the type of the emulsifier nor

the type of chocolate are relevant factors for sam-

ple decomposition.

CONCLUSIONS

The efficiency of some commercially available

emulsifiers as well as of some mixtures thereof

was investigated by using two base chocolate

recipes. Different contributions of both type and

concentration of the emulsifier to the rheological

properties of chocolate masses allow producers to

adjust processing parameters to their specific

needs. The findings indicate that, if necessary, the

commonly used emulsifier lecithin may easily be

substituted by alternative products.

In addition to the influence on viscosity and yield

stress, emulsifiers also show effects on the cry-

stallisation process. Therefore, manufacturers

should take into account that pre-crystallisation

profiles and, consequently, solidification times areaffected by the emulsifying agent. As regards filled

chocolate products, physical shelf life expressed

0

3

6

9

12

Penetration depth [mm]

0 10 20 30 40 50 60 70

Storage time [d]

LYNL/PGPRPGPRLYNL/PGPRPGPR

0

5

10

15

20

Penetration depth [mm]

0 10 20 30 40 50 60 70

Storage time [d]

LYNL/PGPRPGPRLYNL/PGPRPGPR




333

in terms of stability towards phase exchanges is

one of the most important consumer-relevant pro-

perties. Differences caused by the type of emulsi-

fier can be explained by interactions between cho-

colate and filling.

ACKNOWLEDGEMENTS

This study was granted by Arbeitsgemeinschaft

industrieller Forschungsvereinigungen (AiF) via

Forschungskreis der Ernährungsindustrie (FEI) as

AiF-FV 11794. The authors would like to thank

Deutsche Forschungsanstalt für Lebensmittel-

chemie (DFA, Munich) and the involved

companies for supplying material and helpful

discussions.

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Lebensmitteln. Berlin, Heidelberg:

Springer Verlag, Akademie Verlag, 1985.

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[4] G. Ziegleder, “Kristallisation von Kakao-

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[5] Y. Zeng, “Impf- und Scherkristallisation

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[6] B. Schantz and L. Linke, “Der Einfluss von

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2Rheol - Choco Rheology 329