Emulsion Stabilizing Properties of Pectin

Emulsion stabilizing properties of pectin

J. Lerouxa, V. Langendorffa, G. Schickb, V. Vaishnavc, J. Mazoyera,*

aResearch Center, Degussa Texturant Systems France SAS, Baupte F50500, FrancebDegussa Texturant Systems GmbH, 85354, Freising, Germany

cDegussa Texturant Systems Inc, Atlanta, GA 30340, USA

Received 19 July 2002; revised 18 November 2002; accepted 16 December 2002

Abstract

Citrus pectin and beet pectin are able to reduce the interfacial tension between an oil phase and a water phase and can be efficient for the

preparation of emulsions. Investigations were made to evaluate the effect of various parameters of pectin on its emulsifying capacity. Orange

and rapeseed oils emulsions were prepared with pectin as an emulsifier. They were then separated by centrifugation and the pectin fraction

remaining in the aqueous phase was analyzed. It was found that the molecular weight, protein and acetyl contents influenced significantly the

emulsifying properties. It was observed that for both citrus and beet pectin, the fraction which became associated with the oil contained much

more protein than the fraction in the aqueous phase. It is suggested that protein associated with the pectin played a key role in the stabilization

of the emulsion. Our experiments indicated that depending on the pectin source, beet or citrus, only a limited quantity is adsorbed on the oil

surface. The de-acetylated beet pectin maintained a good emulsifying ability but the chemically acetylated citrus pectin gave better results

than the non-acetylated citrus pectin. It was inferred that acetyl groups could also contribute to emulsion stability. It is likely that they act by

reducing the calcium bridging flocculation. A model is proposed to explain the emulsifying function of pectin.

q 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Pectin; Sugar beet; Citrus; Emulsifying properties; Protein; Acetyl; Molecular weight

1. Introduction

Pectin is a well-known food additive which is mainly

used for its gelling and stabilizing abilities. It is extracted

from the plant cell wall, especially citrus peels, apple

pomace and sugar beet pulps. Pectin is used to make gels in

aqueous media containing sugar and acid. Pectin is also able

to stabilize dairy protein under acidic conditions, a role

previously explained by Parker, Boulenguer and Kravtch-

enko (1994). The two mentioned applications account for

the main worldwide consumption of pectin, but a few other

functionalities have also been reported. Kertesz (1951), in

an extensive review of pectin, also mentioned its emulsify-

ing properties. As early as 1927, the use of pectin as an

emulsifying agent in various applications such as flavor,

mineral and vegetable oils emulsions and mayonnaise, was

suggested (Rooker, 1927).

Pectin has a very complex structure which depends on

both its source and the extraction process. Numerous studies

contributed, and continue, to elucidate the structure of

pectin. Basically, it is a polymer of a-D-galacturonic acid

with 1-4 linkages (Aspinall, 1980). This ain chain is

regularly interrupted by some rhamnogalacturonan seg-

ments which combine galacturonic acid residues and a-L-

rhamnopyranose by a 1-2 linkage (Schols & Voragen,

1996). Rhamnogalacturonan contains lateral chains which

comprise of arabinan and arabinogalactan linked on O-4 or

O-3 of the rhamnosyl units (Aspinall, 1980; Selvendran,

1985). The galacturonic acid of the backbone is partially

methyl-esterified and O-acetylated at C-2 or C-3. In

addition, lateral chains have some phenolic acids such as

ferulic acid, which are linked to the arabinose and galactose

via ester linkages (Fry, 1983).

It is worthwhile to note that the plant primary cell wall

contains proteins and particularly hydroxyproline-rich

proteins (Lamport & Northcote, 1960). There is no strong

evidence for any covalent linkages between pectin and

glycoprotein (Ridley, O’Neill, & Mohnen, 2001). However,

within the analyses of various industrial pectin samples

Kravtchenko, Voragen, and Pilnik (1992) have reported the

presence of hydroxyproline rich protein in pectin which was

0268-005X/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.

doi:10.1016/S0268-005X(03)00027-4

Food Hydrocolloids 17 (2003) 455–462

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* Corresponding author. Tel.: þ33-23-371-34-83; fax: þ33-23-371-

34-92.

E-mail address: [email protected] (J. Mazoyer).

http://www.elsevier.com/locate/foodhyd

not completely removed by copper purification. Recently

Oosterveld, Voragen, and Schols (2002) suggested that an

arabinogalactan-protein was linked to the pectin extracted

from hops.

A comparison of the relevant chemical features of pectin

from the three main sources is given in Table 1. It clearly

illustrates that sugar beet is different in terms of protein and

acetyl content.

There is no clear explanation about the origin of the

emulsifying function of pectin. Hypothesizing that a high

acetyl content could enhance the hydrophobicity of pectin,

Dea and Madden (1986) studied the emulsifying ability of

sugar beet pectin in relation to its chemical structure. They

concluded that there was no evidence for a relationship

between chemical composition and emulsifying ability.

Nevertheless, according to Endreß and Rentschler (1999),

the emulsifying ability of beet pectin can be explained by

the presence of acetyl groups (4–5%). In our previous

publication, Akhtar, Dickinson, Mazoyer, and Langendorff

(2001), we studied the emulsifying properties of citrus

pectins. This paper concluded that citrus pectin, which is

low in acetyl, may have an interesting emulsifying capacity.

The pectin with a low molecular weight of about 60–

70 kg mol21 and a high degree of methoxylation shown the

best emulsifying properties. Only a small part of the pectin

which is associated with most of the protein became

adsorbed onto the oil.

Pectin is not the only gum to be reported with

emulsifying properties. Lotskar and Maclay (1943) have

found good emulsifying abilities with various gums, e.g.

tragacanth, acacia, karaya and pectin. Gum arabic (Acacia

senegal) is a commercially important emulsifying agent

for flavor oils. It is generally used at high concentrations

of about 15–25% w/w in the emulsions. Its emulsifying

ability is due to a small amount of protein which is

covalently bound to a highly branched polysaccharide

structure (Dickinson, Elverson, & Murray, 1989; Dick-

inson, Galazka, & Anderson, 1991; Randall, Phillips, &

Williams, 1988). In addition, other polysaccharides have

been reported with emulsifying abilities, Garti and

Reichman (1993) demonstrated that micro-crystalline-

cellulose, guar and locust bean gum were surface active,

not due to protein moieties, but due to ‘steric’ and

‘mechanical’ stabilization mechanisms. Huang, Kakuda,

and Cui (2001) reported the efficiency of various

hydrocolloids gums in stabilizing emulsions.

The aim of this study was to compare various pectins,

differing in origin and molecular weight, in terms of their

emulsifying capacity and to propose a relationship between

structure and emulsifying property.

2. Experimental

2.1. Materials

High-molecular-weight pectins were extracted from

dried citrus peels or sugar beet pulp by hydrolysis with

nitric acid at pH 1.6 for 1 h at 80 8C. Depolymerized citrus

pectin (DCP) samples were prepared by heating the

extraction slurry at 120 8C for 10 min. A range of various

molecular citrus pectin, from 13 to 186 kg mol21, were

prepared according to the procedure described by Akthar,

Dickinson, Mazoyer, and Langendorff (2002). After purify-

ing the slurries by filtration, the slurry syrups were

concentrated by ultrafiltration, and the pectin samples

were recovered by precipitation in isopropyl alcohol. The

products were then dried and ground.

Table 2 provides characteristics of the samples. Molecu-

lar weight was measured by light scattering. The degree of

methoxylation was determined by titration and the galac-

turonic acid content was determined by titration and

colorimetry using the metahydroxydiphenyl method

described by Thibault (1979). Protein content ðN £ 6:25Þ

was determined by the Kjeldahl procedure. The acetyl

content was measured according to the colorimetric dosage

(McComb & McCready, 1957).

Table 1

Galacturonic acid (GalA), rhamnose (Rha), arabinose (Ara), xylose (Xyl),

galactose (Gal) and protein contents (wt%), degree of methoxylation and

degree of acetylation of some acid extracted pectin

Apple Citrus Beet

GalAa 73.1 79.2 62.4

Rhaa 2.3 1.4 5.4

Araa 4.4 1.1 5.1

Xyla 1.7 0.2 0.2

Gala 4.2 2.4 9.3

NS (1) 12.6 5.1 19.9

Protein 1.6b 3–3.3b 10.4c

DAc 5b 1.4–1.6b 16a–35d

DMa 74 72 54

Total neutral sugar is the sum of the mentioned sugars.a Axelos and Thibault (1991).b Kravtchenko, Pilnik, and Voragen (1992).c Thibault (1988).d Levigne, Ralet, and Thibault (2002).

Table 2

Source, molecular weight ðMwÞ; degree of methoxylation (DM), galac-

turonic acid (GalA), acetyl and protein contents (wt%) of the pectin

samples. (CP: high molecular weight citrus pectin, DCP1, 2 and 3:

depolymerised citrus pectin, BP1 and 2: sugar beet pectin)

Samples ID Source Mw

(kg/mole)

DM

(%)

GalA

(%)

Acetyl

(%)

Protein

(%)

CP Citrus 162 72.9 79 – 0.93

DCP1 Citrus 38 66.3 81.5 – 21.61

DCP2 Citrus 72 76.6 83.3 0.46 1.32

DCP3 Citrus 62 71.4 80.2 0.39 0.77

BP1 Beet – 57.1 79.2 1.93 1.95

BP2 Beet – 61.2 81.6 2.98 2.28

J. Leroux et al. / Food Hydrocolloids 17 (2003) 455–462456

Rapeseed oil (RSO) (Bouton d’or, France) was pur-

chased in the local shops and the Bresil orange oil (OO) was

provided by Degussa Food and Flavors (Grasse, France).

Gum arabic was the Instant Gum AS IRX 40830 (CNI,

France) and the synthetic resin was Ester Gum 8BG

(Hercules BV, The Netherlands). Paraffin oil was purchased

from Prod’Hyg Laboratories, France.

2.2. Interfacial tension

The interfacial tensions were measured using the Du

Nouy ring method with a tensiometer CS-Du Nouy 70535,

CSC Scientific Company. The tension was measured at the

interface between the paraffin oil and a 2% w/w pectin

solution in a pH 3.8 sodium citrate, citric acid buffer 0.02 M.

2.3. Emulsion preparation and characterization

Pectin powder was added slowly to a solution containing

0.1% w/w sodium benzoate and 0.2% w/w citric acid at

room temperature with gentle stirring. The pH of the

resulting pectin solution was adjusted to pH 3.5 by adding

1 M NaOH.

Oil-in-water emulsions (20% w/w rapeseed or orange

oil) were prepared at room temperature using a laboratory-

scale homogenizer ALM2 (Pierre Guerin, France) with

three passes at 200 bars. The orange oil was first mixed with

Ester Gum 8BG in order to increase its density. The two

phases were then mixed by a magnetic stirrer for 30 min

before being homogenized. The droplet-size distributions of

the emulsions were measured using a static laser light-

scattering analyzer (Malvern Mastersizer 2000) equipped

with liquid dispersing tank (hydro 2000S). The emulsifying

ability was assessed by checking the shape of the

distribution and measuring the value of the average droplet

size.

The average droplet size was characterized by the

equivalent volume mean diameter, D½4; 3�; defined by:

D½4; 3� ¼X

inid

4i =X

inid

3i ;

where ni is the number of droplets of diameter di: This value

is similar to an average volume (or weight if the density is

constant) of a distribution we could have obtained by

sieving. This means that only one droplet of a large size

generates an increase in the mean diameter. Droplet size

determination was performed after 24 h storage at room

temperature and after a further 7 and 30 days in order to

assess the stability of the emulsion.

2.4. Polysaccharide and protein adsorption

The amount of pectin adsorbed onto the droplet surface

following emulsification was inferred from measurements

of the concentration of polysaccharide remaining in the

serum phase after centrifugation (60,000g for 2–4 h).

The pectin was recovered from the aqueous phase by

precipitation into isopropyl alcohol. The precipitate was

washed in pure alcohol before drying and grinding. The

proportion and composition of pectin associated with the

droplets was calculated from the concentration and

composition of pectin present in the aqueous phase before

emulsification and that found in the serum layer after

centrifugation.

2.5. Acetylation and de-acetylation procedures

The acetylation of pectin was performed according to the

procedure of Carson and Maclay (1946). 5 g of commercial

HM-citrus pectin (Degussa Texturant Systems, DM72.0,

Acetyl cont. 0.56%) were dissolved in 150 ml of formamide.

Then, 5 ml of pyridine and variable amounts of acetic

anhydride (1, blank: 0 ml; 2: 1.25 ml; 3: 2.5 ml, and 4:

5.0 ml) were added and the solution was stirred for 2 h at

30 8C. The products corresponding to each amount of acetic

anhydride were identified as ACP1, ACP2, ACP3 and ACP4.

The acetylated pectin was precipitated, depending on the

degree of substitution, with acidified methanol or acetone.

Beet pectin was de-acetylated by slowly adding 3.5 ml of

50% sodium hydroxide in water to a solution of 15 g of beet

pectin in 400 ml of water and stirring for 20 h at 6 8C. After

careful neutralization under thorough homogenization with

7.5 ml of 25% hydrochloric acid in water, the saponified and

de-acteylated beet pectin was precipitated with 1 l of

isopropanol and filtered. The product was washed twice

with 400 ml of isopropanol, dried and ground (Yield:

12.2 g). The resulting LM-beet pectin (DM7.4) was re-

methylated by dispersing the pectin powder in methanolic

hydrochloric acid. Therefore, 3.6 ml of acetic chloride were

added dropwise to 90 ml of methanol. After 9 g of the pectin

obtained above had been added, the slurry was stirred for

24 h at 20 8C. The resulting de-acetylated HM-beet (DA-

BP5) was recovered by filtration, washed with 70% aqueous

methanol and pure methanol. Finally, the dried product was

ground.

3. Results and discussion

3.1. Interfacial activity of various pectin samples

First, the interfacial properties of the differing pectin

samples at 2% w/w concentration were examined in

comparison with gum arabic at 15% w/w concentration.

Gum arabic serves as the comparison since it is the

commercial emulsifying gum and is generally used at this

range of concentration. The observations are shown in

Table 3. The most significant reductions of tension are

observed for Depolymerised and beet pectins. There is no

clear theory to explain why the low molecular weight

pectins are better than those of higher molecular weights. It

is likely that kinetic effects may be involved in such

J. Leroux et al. / Food Hydrocolloids 17 (2003) 455–462 457

behavior. The interfacial tensions were measured immedi-

ately after the two phases were in contact. One might

suggest that high molecular products which develop more

viscous solutions should move more slowly to the interface.

Thus waiting for an equilibrium, might have given different

results. Huang, Kakuda and Cui (2001) waited for

equilibrium for a period of 30 min and observed a more

significant tension reduction for a non-depolymerised

pectin. Garti and Reichman (1994) also observed this

kinetic effect for more diluted guar solutions.

Moreover, we should also take into account the

conformational aspect of pectin which is well known to be

different from gum arabic. Pectin is a semi-flexible polymer

whereas gum arabic adopts a random coil conformation.

This may account for the surface coverage.

It is interesting to note that pectin, at 2% concentration,

had an effect similar to the gum arabic at 15% on the

interfacial tension reduction.

3.2. Emulsifying ability of citrus and beet pectin

Fig. 1, compares the particle size distributions of

emulsions made with gum arabic ðD½4; 3� ¼ 0:31 mmÞ;

depolymerised citrus ðD½4; 3� ¼ 0:40 mmÞ and citrus pectin

ðD½4; 3� ¼ 0:80mmÞ: It demonstrates that pectin is able to

make emulsions in the same way as gum arabic. Never-

theless, DCP gave better results in terms of both distribution

profile and mean diameter.

Non-depolymerised citrus pectin showed a second peak

which was attributed to the beginning of a calcium bridging

flocculation (Akthar, Dickinson, Mazoyer, & Langendorff,

2002). In the same study, the effect of molecular weight of

citrus pectin was reported, it was established that a pectin of

high DM and a molecular weight of 70 kg mol21 gave the

best results in terms of particle size diameter and stability on

creaming. The effect of pectin molecular weight is shown in

Fig. 2 where DCPs of molecular weights between 50 and

80 kg mol21 gave the best results in terms of particle size

and stability.

It is noticeable that these observations are rather

consistent with the reductions of the interfacial tension

results. However, very low molecular weight pectin, even if

it reduces the interfacial tensions, seems to lose a part of its

emulsifying capacity giving coarser emulsions. It was

tentatively explained in our previous paper that, since

emulsions made with high molecular pectins may undergo a

calcium bridging flocculation, a reduction of the chain

length could reduce the probability of the interactions.

In comparison with the DCP, beet pectin gave better

results. Fig. 3 shows a comparison between these two

pectins in rapeseed oil emulsions as a function of pectin

concentration. It was observed that beet pectin was very

efficient for producing a fine emulsion at 2 wt%, whereas

citrus pectin required higher concentrations (.4 wt%).

In terms of particle size distribution profile, beet pectin

produced some Gaussian profiles which were very stable on

storage.

Thus once again, it is shown that pectin is able to act as a

food emulsifier able to stabilize oil in water emulsions even

Table 3

Interfacial tensions of paraffin oil/2% w/w pectin solutions at pH 3.8, at

25 8C, in (mN/m)

Interfacial tension

Buffer pH 3.8 36.3

Citrus pectin (CP) 31.3

Citrus pectin (DCP1) 20.2

Beet pulp pectin (BP1) 19.4

Gum Arabica 19.7

a Gum Arabic solution 15%.

Fig. 1. Particle size distribution profiles after 24 hours of emulsions made

with orange oil 10%, 10% ester gum and 4% w/w of high molecular weight

pectin ( £ ), of DCP (—)mm and 25% of gum arabic (W).

Fig. 2. Particle mean diameter D½4; 3� (mm) of emulsions made with orange

oil 10% and 10% ester gum in 4% w/w of various molecular weight citrus

pectin solution. Measurements were made after 24 h, 7 and 20 days storage

at room temperature 24 h ( £ ), 7 days (K) and 30 days (A).


those containing rather high concentrations of oil phase

(20%). Pectin was good in both the flavor oil and vegetable

oil emulsions we studied. It is evident that beet pectin was

more efficient than citrus pectin since it produced finer

particle distribution profile and more stable emulsions at

lower pectin concentrations. In our previous study (Akthar,

Dickinson, Mazoyer, & Langendorff, 2002) on citrus pectin,

we observed that the pectin fraction which became

associated which the oil droplets contained almost all the

protein fraction present in the hydrocolloid. Therefore, it is

suggested that pectin could behave in the same way. The

emulsifying properties of gum arabic are connected to a

small fraction of the gum rich in protein (Randall, Phillips,

& Williams, 1988).

3.3. Polysaccharide adsorption

The adsorption of pectin onto the oil was studied in

various media. The adsorption of the DCP onto the rapeseed

oil, as a function of the pectin concentration, is shown in

Fig. 4. The adsorbed pectin amount increases linearly up to

about 4% pectin meaning that a constant fraction of the

pectin (about 5%) is adsorbed. It also could be inferred that

4% pectin in the emulsion should correspond to the surface

coverage of the droplets, this concentration will be called the

adsorption threshold. However, we must be prudent since,

beyond a certain concentration, the increase of viscosity

makes the phase separation difficult. For high pectin

concentrations some oil may remain in the serum layer. In

the case of DCP with orange oil, was not possible to carry

Fig. 3. Particle size (D½4; 3� in mm) after 24 h storage at 25 8C of emulsions

made with rapeseed oil at 20% in DCP (A) and beet pectin ( £ ) vs pectin

concentration.

Fig. 4. Adsorbed pectin ( £ ) and adsorbed pectin fraction (A) in emulsions

made with rapeseed oil at 20% in DCP as a function of the pectin

concentration.

Fig. 5. Adsorbed pectin ( £ ) and adsorbed pectin fraction (A) in emulsions

made with orange oil at 20% in beet pectin as a function of the pectin

concentration.

Table 4

Weight fraction and quantity of adsorbed of pectin in various emulsions

with 20% rapeseed oil (RSO) or orange oil with DCP and beet pectin. The

pectin concentration corresponds to the beginning of the adsorption

threshold

Beet pectin

orange oil

Beet

pectin

RSO

Citrus

pectin

RSO

Total pectin

concentration

in the emulsion

(w%

emulsion)

2.0 1.5 4.0

Weight fraction

of pectin adsorbed

onto the oil

(w% total

pectin)

9.8 14.9 4.7

Quantity of pectin

adsorbed onto the oil

(mg/100 g

emulsion)

196 224 188

The system of citrus pectin in orange oil is not given here because the

threshold could not be observed. The higher pectin concentration required

made the solution to be too much viscous to be separated correctly.


out a correct phase separation at high pectin concentrations.

Therefore, for this system, no threshold could be observed.

For this reason, further chemical analysis of the pectin

structure will be made at lower concentrations. In the case of

the beet pectin in orange oil (Fig. 5), the results are rather

different. The ‘adsorption threshold’ appears at a lower

concentration, 2% instead of 4% for DCP. Curiously, there

is an increase of adsorbed fraction as a function of the pectin

concentration below the maximum, whereas it was steady

with citrus pectin. The maximum of adsorption fraction is at

10%, i.e. more than with the citrus pectin.

The values of the adsorption threshold for the different

systems and the weight fractions of adsorbed pectin for

the three systems for which we could make observations

are given in Table 4. It was interestingly observed that

the quantities of adsorbed pectins are rather constant

whatever the system.

Thus, in comparison with the citrus pectin, more beet

pectin adsorbs onto the oil more and therefore less pectin

is required to cover the droplet surface. These obser-

vations are consistent with the emulsion droplet size

analysis.

Comparisons between protein and acetyl contents in the

whole initial pectin and in the adsorbed fraction are given in

Table 5. This comparison is made at a pectin concentration

of 1 wt% in the emulsion, it is below the maximum of

adsorption. Thus, all of the ‘active’ fraction of the pectin is

assumed to be attached to the oil. The adsorbed pectin

shows a significant increase in both protein and acetyl

content. It is observed that the composition of the adsorbed

pectin, in terms of protein and acetyl contents, is more

dependant on the nature of the oil than on the source of

the pectin, e.g. in the rapeseed oil, even if the original

pectins are different, the adsorbed fractions seems to be very

similar.

The pectin which reacts with the orange oil seems to have

more protein, than that for the rapeseed oil. This is probably

why less beet pectin than citrus pectin is required to make an

emulsion with RSO. From a global point of view, as beet

pectin contains more protein than citrus pectin, much less

beet pectin is necessary to reach the adsorption threshold.

3.4. Acetylation and de-acetylation experiments

In order to provide more information about the

contribution of the acetyl groups to emulsifying function-

ality, two further experiments were conducted: first, the

acetylation of citrus pectin which is normally poorly

acetylated and has low emulsifying properties and secondly

the de-acetylation of a normally acetylated sugar beet pectin

which has good emulsifying properties. The emulsifying

ability of acetylated citrus pectins are presented in Table 6.

This table gives the D½4; 3� values after 24 h storage of the

emulsions made with pectins as a function of the levels of

acetylation in comparison with beet pectin. This experiment

demonstrates that citrus pectin requires higher amounts of

acetyl than the beet pectin to be as efficient.

The de-acetylated beet pectin did not show any

significant loss in emulsifying capacity (Table 7). There-

fore, although it seems the acetyl groups are more common

in the pectin fraction which adheres the oil phase, their

presence is not an absolute requirement with respect to the

emulsifying capacity.

Table 5

Weight percentage of protein and acetyl contents in initial and adsorbed pectins in various emulsions made with 1% pectin

BP1/OO BP1/RSO DCP2/OO DCP3/RSO

Whole

pectin

Adsorbed

fraction

Whole

pectin

Adsorbed

fraction

Whole

pectin

Adsorbed

fraction

Whole

pectin

Adsorbed

fraction

Protein (w%) 1.95 21.2 1.95 7.9 1.32 13.8 0.77 7.8

Acetyl (w%) 1.93 3.9 1.93 2.7 0.46 2.7 0.39 2.1

Table 6

Particle size (D½4; 3� at 24 h in mm) of emulsions made with 20% of

weighted orange oil and 2 wt% pectin of chemically acetylated citrus

pectins in comparison to sugar beet pectin (SBP) ACP: acetylated citrus

pectin, BP sugar beet pectin

Acetyl (%) Emulsion D½4; 3� (mm)

ACP1 0.57 2.76

ACP2 2.24 2.67

ACP3 5.59 1.31

ACP4 8.73 0.65

BP 2–4 0.4–0.5

Table 7

Particle size after 24 h and 7 days storage ðD½4; 3�24 h;D½4; 3�7dÞ of

emulsions made with 20% of weighted orange oil and 2 wt% pectin of

chemically de-acetylated sugar beet pectins. DA-SBP 5: de-acetylated

sugar beet pectin

Pectin ID Acetyl (%) Protein (%) D½4; 3�24 h (mm) D½4; 3�7 d (mm)

SBP 1.93 1.95 0.52 0.64

DA-SBP 5 0.17 2.19 0.68 0.73


3.5. The effect of calcium

The calcium content of the pectin seems to have an

important effect on the emulsion stability. Akthar, Dick-

inson, Mazoyer, and Langendorff (2002) mentioned the

likelihood that calcium would induce a bridging floccula-

tion. This calcium effect was also tested on sugar beet

pectin. In this investigation, a sample of sugar beet pectin

was washed in acidified isopropyl alcohol in order to lower

the calcium content and the product was tested in emulsions.

In this way, the calcium content was reduced from

5700 ppm down to 2060 ppm. The particle size distributions

of an orange oil emulsion made with 2% pectin of both

decalcified and non decalcified pectins are shown in Fig. 6.

The d4.3 was reduced from 0.564 to 0.371 mm. We can

observe that the distribution becomes almost perfectly

Gaussian without any additional peak at about 5 mm. Thus,

even with the acetylated beet pectin, the acidified alcohol

washing leads to better results which are probably due to the

reduction of calcium.

4. Conclusion

In this study, we have shown that pectin is definitely able

to produce fine and stable emulsions in the same manner as

gum arabic but at much lower dosage. Among the various

pectin sources, sugar beet has the best emulsifying

properties.

The observed emulsifying properties of pectin are most

probably due to the protein residues present within the

pectin. Thus the model of association to oil droplets may be

similar to that of gum arabic as proposed by Randall,

Phillips, and Williams (1989). However, there is

a conformational difference between pectin and gum arabic.

Pectin is a semi-flexible polymer whereas arbinogalactan–

protein complex which is the most active of part gum arabic

has a coil conformation with a small radius of gyration and

equivalent sphere hydrodynamic radius. Since less pectin is

required to cover the oil droplet surface than gum arabic, it

may be inferred that pectin takes up a greater volume around

the droplets. This could be due to the more extended

conformation of the pectin molecule.

Pectin chains are able to strongly complex calcium

and some interchain associations may arise due to

calcium binding. This interaction may cause flocculation.

Since any acetyl groups may reduce calcium sensitivity,

they also contribute to the emulsion stability avoiding the

bridging flocculation. Thus the combination of acetyl

groups and protein is suggested to give the pectin its

emulsifying properties (see suggested model in Fig. 7).

The more favorable properties of sugar beet in

comparison with citrus pectin may be explained by the

fact that beet pectin contains more protein and more acetyl

groups but it could also be due to possible conformational

differences between the two pectin molecules.

Acknowledgements

The authors gratefully acknowledge K. Born and the staff

of the Research Center of Degussa Texturant Systems S.A.S

for their help, especially, A. Bourdais and D. Callais for

their kind assistance and S. Wildmoser for the preparation of

Fig. 6. Particle size distribution profiles of emulsions made with orange oil

10% and 10% ester gum in 2% w/w beet pectin (dashed line, D½4; 3� ¼ mm)

and de-calcified (full line, D½4; 3� ¼ mm).

Fig. 7. Hypothetical model of emulsion stabilization by pectin.


acetylated and de-acetylated pectin samples. Thanks also go

to Professor E. Dickinson for helpful discussions and to Dr

M Akthar.

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Emulsion Stabilizing Properties of Pectin