Upload
farah-bahri
View
95
Download
2
Embed Size (px)
Citation preview
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
www.elsevier.com/locate/foodhyd
* Corresponding author. Tel.: þ33-23-371-34-83; fax: þ33-23-371-
34-92.
E-mail address: [email protected] (J. Mazoyer).
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).
J. Leroux et al. / Food Hydrocolloids 17 (2003) 455–462458
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.
J. Leroux et al. / Food Hydrocolloids 17 (2003) 455–462 459
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
J. Leroux et al. / Food Hydrocolloids 17 (2003) 455–462460
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.
J. Leroux et al. / Food Hydrocolloids 17 (2003) 455–462 461
acetylated and de-acetylated pectin samples. Thanks also go
to Professor E. Dickinson for helpful discussions and to Dr
M Akthar.
References
Akhtar, M., Dickinson, E., Mazoyer, J., & Langendorff, V. (2002).
Emulsion stabilisation of depolymerised pectin. Food Hydrocolloids,
16, 249–256.
Aspinall, G. O. (1980). Chemistry of cell wall polysaccharides. The
Biochemistry of Plants, New York: Academic Press.
Axelos, M. A. V., & Thibault, J.-F. (1991). Influence of the substituents of
the carboxyl and of the rhamnose content on the solution properties and
flexibility of pectins. International Journal of Biological Macromol-
ecules, 13, 77–82.
Carson, J. F., & Maclay, W. D. (1946). The acetylation of polyuronides
with formamide as a dispersing agent. Journal of American Chemical
Society, 68, 1015–1017.
Dea, I. C. M., & Madden, J. K. (1986). Acetylated pectic plysaccharides of
sugar beet. Food Hydrocolloids, 1(1), 71–88.
Dickinson, E., Elverson, D. J., & Murray, B. S. (1989). On the film-forming
and emulsion stabilising properties of gum arabic: dilution and
flocculation aspect. Food Hydrocolloids, 3, 101–114.
Dickinson, E., Galaska, V. B., & Anderson, D. M. (1991). Emulsifying
behaviour of gum arabic. Carbohydrate Polymers, 141, 373–392.
Endreß, H. U., & Rentschler, C. (1999). Chances and limit for the use of
pectin as emulsifier—Part 1. The European Food and Drink Review,
Summer, 49–53.
Fry, S. C. (1983). Feruloylated pectins from the primary cell wall:
their structure and possible functions. Planta, 157, 11–123.
Garti, N., & Reichman, D. (1993). Hydrocolloids as food emulsifiers and
stabilizers. Food Structure, 12, 411–426.
Garti, N., & Reichman, D. (1994). Surface properties and emulsification
activity of galactomannans. Food Hydrocolloids, 8(2), 155–173.
Huang, X., Kakuda, Y., & Cui, W. (2001). Hydrocolloids in emulsions:
particle size distribution and interfacial activity. Food Hydrocolloids,
15, 533–542.
Kertesz, Z. I. (1951). The pectic substances. New York: Interscience
Publishers, Inc.
Kravtchenko, T. P., Voragen, A. G. J., & Pilnik, W. (1992). Analytical
comparison of three industrial pectin preparations. Carbohydrate
Polymers, 18(1), 17–25.
Lamport, D. T. A., & Northcote, D. H. (1960). Hydroxyproline in primary
cell walls of higher plants. Nature, 188, 665–666.
Levigne, S., Ralet, M.-C., & Thibault, J.-F. (2002). Characterization of
pectins extracted from fresh sugar beet under different conditions using
an experimental design. Carbohydrate Polymers, 49(2), 145–153.
Lotskar, H., & Maclay, W. D. (1943). Pectin is an emulsifying agent,
comparative efficiencies of pectin, tragacanth, karaya and acacia.
Industrial and Engineering Chemistry, 35(12), 1294–1297.
McComb, E. A., & McCready, R. M. (1957). Determination of acetyl in
pectin and in acetylated carbohydrate polymers. Analytical Chemistry,
29(5), 819–921.
Oosterveld, A., Voragen, A. G. P., & Schols, H. A. (2002). Characterization
of hop pectins shows the presence of an arabinogalactan protein.
Carbohydrate Polymers, 49(4), 407–413.
Parker, A., Boulenguer, P., & Kravtchenko, T. P. (1994). Effect of the
addition of high methoxyl pectin on the rheology and colloidal stability
of acid milk drinks. In K. Nishinari, & E. Doi (Eds.), Food
hydrocolloids: Structure, properties and functions (pp. 307–312).
New York: Plenum Press.
Randall, R. C., Phillips, G. O., & Williams, P. A. (1988). The role of
proteinaceous component on the emulsifying properties of gum arabic.
Food Hydrocolloıds, 2(2), 131–140.
Randall, R. C., Phillips, G. O., & Wiliams, P. A. (1989). Fractionation and
characterization of gum from acacia senegal. Food Hydrocolloıds,
3(1), 65–75.
Ridley, B. L., O’Neill, M. A., & Mohnen, D. (2001). Pectins: structure,
biosynthesis, and oligalacturonide-related signaling. Phytochemistry,
57, 929–967.
Rooker, W. A. (1927). New uses of fruit pectin. The Fruit Products Journal
and American Vinegar Industry, 7(1), 11.
Schols, H. A., & Voragen, A. G. J. (1996). Complex pectin: structure
elucidation using enzymes. In J. Visser, & A. G. J. Voragen (Eds.),
Pectins and Pectinases (Vol. 14) (pp. 3–19). Progress in Biotechnol-
ogy, Amsterdam: Elsevier.
Selvendran, R. R. (1985). Developments in the chemistry and biochemistry
of pectic and hemicellulosic polymers. Journal of Cell Science,
2(Suppl.), 51–88.
Thibault, J.-F. (1979). Automatisation du dosage des substances pectiques
par la methode au meta-hydroxydiphenyl. Lebensmittel 2
Wissenschaft þ Technologie, 12, 247–251.
Thibault, J.-F. (1988). Characterization and oxidative crosslinking sugar-
beet pectins extracted from cossetes and pulps under different
conditions. Carbohydrate Polymers, 8, 209–223.
J. Leroux et al. / Food Hydrocolloids 17 (2003) 455–462462