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Contents lists available at ScienceDirect

Food and Bioproducts Processing 

 j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / f b p

Short communication

Effect of extraction conditions on yield and degree of 

esterification of durian rind pectin: An experimental design

Wong Weng Wai, Abbas F.M. Alkarkhi, Azhar Mat Easa ∗

School of Industrial Technology, 11800, Universiti Sains Malaysia, Minden, Penang, Malaysia

a b s t r a c t

The effect of time (1 and 4 h), pH (2.0 and 2.5) and temperature (80 and 90 ◦C) on yield and degree of esterification

(DE) of durian rind pectin was investigated. The yield and DE of the extracted pectin ranged from 2.1 to 10.3% (w/w,

based on dryweight of durianrind) and45.6–64.8% respectively. Yield wassignificantly affected bytime,temperature

and pH, and interactions between temperature and pH, and heating time and pH. DE was significantly affected by

heating time and pH, and interactive effects of temperature and pH, and heating time and pH. The extraction yield

was not related to DE. By considering pectin yield and DE, the acid extraction of durian rind pectin at 80 ◦C, for 4h

and at pH 2.5 could be suitable.

© 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Keywords:   Durian rind pectin; Yield; Degree of esterification; Experimental design; Regression model

1. Introduction

Durian (Durio zibethinus), a tropical fruit native to Southeast

Asia, is oneof themosthighly valued anddesiredfruits among 

Southeast Asians due to its distinct flavour and unique taste.

The fruit is ovoid or ovoid-oblong to nearly round shaped with

an average size weighing between 2 and 4.5 kg depending on

their varieties (Hokputsa et al., 2004). The rind which usually

weighs more than half of the total fruit weight is green to

yellowish brown, thick and semi-woody with sharply pointed

pyramidal thorns. During the season of durian, the amounts

of rind that disposed as waste could lead to environmentalproblems. This agricultural waste could be further utilized

as a source of valuable materials of commercial importance;

such as particleboard component of construction panels for

energy conservation in building (Khedari et al., 2003),  tablet

binder, tablet disintegrator and gelling agent (Pongsamart and

Panmaung, 1998; Umprayn et al., 1990a,b). Of interest is water-

soluble polysaccharides extracted fromdurian rindcontaining 

high amount pectin (Hokputsa et al., 2004).

Pectin is a complex family of heterogeneous branched

polysaccharides that arise from the primary cell walls and

∗ Corresponding author. Fax: +6 04 6573678.E-mail address: azhar@usm.my (A.M. Easa).Received23 October 2008; Accepted 25 January2010

intercellular regions of higher plants, consisting mainly of  d-

galacturonic acid and neutral sugars, such as   l-rhamnose,

l-arabinose, and d-galactose. The term pectin or pectic sub-

stance describes a group of polysaccharides in which the

presence of partly methyl-esterified galacturonic acid and

rhamnose is a distinctive feature (Voragen et al., 1995). Pectin

with degree of esterification (DE; the percentage of carboxyl

groups esterifiedwith methanol)higher than50%, named high

methoxyl pectin (HMP) forms gel after heating in sugar solu-

tions at concentration higher than 55% and pH lower than 3.5.

Onthe other hand,formation ofgel with a low methoxyl pectin

(LMP; DE < 50%) requires the presence of calcium ions, extend-ing the use of this gelling agent to a broader range of foods.

LMP may be used as a gelling agent in low sugar products,

such as low-calorie jams and jellies, confectionery jelly prod-

ucts, and other foods applications. The heat reversibility of 

LMP gels can be utilized in bakery jams and jellies for glazing,

retorting, microwaving, baking, andsterilizing or pasteurizing.

Durian agro-waste could be used to produce pectin. As far

as we know, there is no published work on the study of the

effect of extraction conditions on the yield and DE of durian

rind pectin. Extraction conditions have been reported to influ-

0960-3085/$ – see front matter © 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.doi:10.1016/j.fbp.2010.01.010

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210   food and bioproducts processing 8 8 ( 2 0 1 0 )   209–214

ence physico-chemical properties of pectin extracted from

other plant sources such as beet (Levigne et al., 2002). There-

fore the objective of this paper was to investigate the effect of 

extraction conditions (temperature, pH and time) on yield and

DE of durian rind pectin.

2. Materials and methods

2.1. Durian rind

Durians fruit (Durio zibethinus) cultivar D24 used in this study

were obtained from a fruit orchard in Relau, Penang, Malaysia

in mid-July 2007. Ripened fruit that dropped naturally were

collected and transported within 3 h on the same morning (at

30 ± 2 ◦C). Fruits were selected for uniformity of size (with the

average weight 2.0 ± 0.5 kg per fruit) and color and freedom of 

defects. A total of 25 fruits were selected for the study.

Durians were cut open with a sharp knife. Durian aril was

separated from the durian rind and seed manually. The rinds

were cut as to eliminate the hard and thorny parts. Later, the

rinds were cut into small pieces (about 0.5 cm thick) to facil-

itate the drying and grinding process. Pieces of durian rind

were placed on aluminum foils and dried in a hot air oven

(AFOS Oven, Hull England) at 70 ◦C for 24 h. The dried durian

rindwere ground intopowderby using a grinder (Micro Univer-

sal Bench Top Grinder, Retsch ZM 100, Germany) and packed

into a sealable plastic bag and stored in desiccators.

2.2. Pectin extraction

The dried durian rind (solid–liquid ratio; 1:9, w/v) was stirred

in a mild acid aqueous solution adjustedto desired pH’s (2.0 or

2.5) with 1N HCl. Then,the solutionwas extracted at 80 or 90 ◦C

for 1 or 4 h. The resulting slurries were filtered through cheese

cloth and allowed to cool to room temperature (25 ◦C). Acidi-

fied ethanol (4% HCl in 95% EtOH) was added in the ratio 1:4

(v/v) and kept for 1 h. The mixture was centrifuged at 1710 × g

for 15 min in a Bench Top Centrifuge (Kubota 5100, Fujioka,

 Japan).

The gel-like precipitate was collected and re-suspended in

distilled water with the ratio 1:4 (w/v). Then, the solution was

rewashed twice with 95% ethanol (1:2, v/v) and centrifuged

for 15 min (1710 × g). Precipitate was collected and dried in a

vacuumovenat25 ◦C for8 h. The pectinwas ground andsieved

(mesh no.60) for further experiments. Yield of pectin obtained

was calculated as:

% Yield =massof extracted pectin

massofair-drieddurianrind  × 100

2.3. Determination of degree of esterification (DE)

The DE of pectin was determined by the titrimetric method of 

Food Chemical Codex (FCC, 1981) and USP 26 NF 21 (2003) with

slight modification. Dried sample (500 mg) was moistened

with 2 ml ethanol and dissolved in 100ml carbon dioxide-free

water. After the sample was completely dissolved, five drops

of phenolphthalein were added, the sample was titrated with

0.5M sodiumhydroxide andthe result was recorded as theini-

tial titer. Then, 10ml of 0.5 M sodium hydroxide were added,

the sample was shaken vigorously, and allowed to stand for

15 min; 10 ml of 0.5 M hydrochloric acid were added and the

sample was shaken until the pink color disappeared. Phe-

nolphthalein (five drops) was added and the solution was

titrated with 0.5M sodium hydroxide to a faint pink color that

persisted after vigorous shaking (end-point). This volume of 

titration was recorded as the saponification titer (the final

titer). The DE was calculated from the following formula:

% DE =thefinaltiter

the initial titer + the finaltiter  × 100

2.4. Statistical analysis

Many experiments involve the study of the effect of two or

more factors, factorial designs are more efficient for this type

of experiment (Montgomery, 2005). This type of designs is very

important to study the effect of several factors, since each

replication of the experiment contains all possible combina-

tions of the levels of the factors. The effect of three factors;

temperature (X1), heating time (X2)andpH(X3). Two responses

in the form of different components of the extract were eval-

uated:

1-   Y 1 = Yield %2-   Y 2 = DE %

Factorial design of type 23 was carried out to study t he

effect of three factors temperature (80–90 ◦C), heating time

(1–4 h) andpH (2.0–2.5) on thetwo responsesmentioned above.

This experiment was carried out in random order to min-

imize the effects of unexpected variability in the observed

responses. Twenty-four runs were required to cover all pos-

sible combinations of factors levels with three replicates.

Experimental data were analyzed to fit the following regres-

sion model with interaction terms

Y  = ˇ0 +

3

i=

ˇiXi +

i<j

ˇijXiX j +

i<j<k

ˇijkXiX jXk   (1)

where ˇ0, ˇi, ˇij and ˇijk are regression coefficients.

3. Results and discussion

3.1. General

The total extraction yield reflected pectin yield even though

some impurities such as degraded pectins and starch might

be present. Table 1 summarizes the results of 24 runs to deter-

mine the yield and DE of pectin produced using different

conditions. The acid-extracted pectin yield ranged from 2.13to 10.25% of the dry weight of the durian rind. Compared to

literature data, these values were generally lower than pectins

extracted from sugar beet and citrus (Yapo et al., 2007; Micard

and Thibault, 1999; Mesbahi et al., 2005)   and banana peel

(Suhaila and Zahariah, 1995; Happi Emaga et al., 2008).

The highest yield was obtained when the durian rind

was extracted at pH 2.0, for 4h, at 90 ◦C. The effects of pH

and time seemed to be the most influential on the pectin

yield. At constant pH and temperature, the yields of pectin

obtained for 1 h of extraction were lower than those of 4 h.

On the other hand, the pectin yields from various extrac-

tions at pH 2.0 were higher than those at pH 2.5. The yield

of pectin has been reported to increase with decreasing pH

(or increasing acid strength) of the extraction (Levigne et al.,

2002).   A similar result of yield was shown at constant pH

and temperature, i.e. increasing the extraction time had a

marked effect on yield. However, when the temperature was

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Table 1 – The results of 24-run with experimental and predicted values.

Input factors Actual values Predicted values

X1   X2   X3   Y 1   Y 2   Y 1   Y 2

80 1 2 5.14 50.39 5.22 48.87

80 1 2 5.04 46.21 5.22 48.87

80 1 2 5.48 50.00 5.22 48.87

90 1 2 5.67 55.43 5.92 54.97

90 1 2 6.20 54.50 5.92 54.97

90 1 2 5.89 54.99 5.92 54.97

80 4 2 8.06 47.84 8.08 47.52

80 4 2 8.01 45.57 8.08 47.52

80 4 2 8.16 49.16 8.08 47.52

90 4 2 8.74 53.72 9.37 51.98

90 4 2 9.13 51.18 9.37 51.98

90 4 2 10.25 51.03 9.37 51.98

80 1 2.5 2.24 64.05 2.26 63.91

80 1 2.5 2.13 62.90 2.26 63.91

80 1 2.5 2.41 64.78 2.26 63.91

90 1 2.5 4.34 64.46 4.36 61.80

90 1 2.5 4.32 59.48 4.36 61.80

90 1 2.5 4.43 61.47 4.36 61.80

80 4 2.5 6.88 57.73 6.87 58.43

80 4 2.5 7.10 57.93 6.87 58.43

80 4 2.5 6.64 59.64 6.87 58.43

90 4 2.5 7.91 47.39 8.46 50.64

90 4 2.5 8.90 51.61 8.46 50.64

90 4 2.5 8.57 52.93 8.46 50.64

increased while pH and time remained constant, the pectin

yield increased slightly. This indicated that yield was higher

when pectin was extracted at pH 2.0 for 4 h irrespective of the

temperature.

3.2. Yield and DE

Factorial design of type 23 was used to evaluate the effect of 

temperature  X1, heating time X2 and pH X3 on the percentage

of yield (Y 1) and DE (Y 2). The results of 24-run including actual

andpredicted valuesare given in Table 1. The regression mod-

els for yield and DE are given by Eqs.  (1) and (2) respectively:

Y 1   = 71.22 − 0.66 X1 − 14.66 X2 − 35.48 X3 + 0.17 X1X2

+ 0.35 X1X3 + 7.11 X2X3 − 0.07 X1X2X3   (2)

Y 2   = −289.47 + 3.41 X1 − 33.51 X2 + 142.76 X3 + 0.48 X1X2

− 1.37 X1X3 + 18.74 X2X3 − 0.27 X1X2X3   (3)

The regression models obtained for yield and DE are sat-

isfactory since the value of the coefficient of determination

Table 2 – The results of analysis of variance (ANOVA) for yield and DE.

Source Sum of squares DF Mean square   F-Value   P-Value

Yield

Model 116.93 7 16.70 124.34 <0.0001

X1   12.13 1 12.13 90.27 <0.0001

X2   84.60 1 84.60 629.74 <0.0001X3   16.50 1 16.50 122.82 <0.0001

X1X2   0.002 1 0.002 0.018   <0.8953

X1X3   1.08 1 1.08 8 <0.0121

X2X3   2.16 1 2.16 16.08 <0.0010

X1X2X3   0.46 1 0.46 3.46   <0.0814

Error 2.15 16 0.13

Total 119.08 23

DE

Model 775.99 7 110.86 31.92 <0.0001

X1   0.17 1 0.17 0.048   <0.8302

X2   165.01 1 165.01 47.51 <0.0001

X3   370.91 1 370.91 106.79 <0.0001

X1X2   20.19 1 20.19 5.81 <0.0283

X1X3   156.93 1 156.93 45.18 <0.0001

X2X3   56.70 1 56.70 16.32 <0.0009

X1X2X3   6.09 1 6.09 1.75   <0.2041

Error 55.58 16 3.47

Total 831.57 23

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(R2) was high and close to 1. The values of  R2 for yield and

DE were 0.98, 0.93, respectively. This indicates that 0.93–0.98

of the total variation was explained by the models and only

(0.02–0.05) of the total variation is unexplained. The relative

contribution of each factor to each response (yield and DE)

was directly measured by the regression coefficient in the fit-

ted model. A positive sign for the regression coefficient in the

fitted model indicates that the ability of the factor to increasethe response, whilst the negative sign indicates the ability of 

a factor to decrease the response.

The results of analysis of variance (ANOVA) for each depen-

dent variable, yield andDE aregivenin Table 2. Theanalysis of 

variance reveals that the models adequately fitted the experi-

mentaldataforyieldandDE.Itcanbeseenthatthemaineffect

for temperature (X1), heating time (X2) ,pH(X3) and interaction

terms between temperature and pH (X1X3), heating time and

pH (X2X3) exhibited strong significant effect on yield, whilst

the interaction between temperature and heating time (X1X2),

and the interaction between temperature, heating time and

pH did not show significant effect on yield. It is interesting 

to note that pH and time were the most significant interac-

tive effect on pectin yield, which is similar to that reported byHappi Emaga et al. (2008) who studied extraction conditions

on pectin yield from banana peel.

Theresultsof analysis forDE showed that themaineffectof 

temperature and the interaction between temperature, heat-

ing time and pH did not exhibited significant effect on DE,

while heating time, pH, interaction between temperature and

Fig. 1 – Three-dimensional response surface plots for yield as a function of (a) temperature and heating time, (b)

temperature and pH and (c) pH and heating time of extraction.

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heating time, interaction between temperature and pH, and

interaction between heating time and pH exhibited a strong 

significant effect on DE. Significant interaction indicates that

the factors work independently, whilst presence of an inter-

action indicates that the difference in response (yield and DE)

at different levels of a factor is not the same at all levels of 

another factor. These three parameters have been recognized

to pose interactive effects on experimental responses during the extraction sugar beet pulp pectin (Yapo et al., 2007).   It

is to note that temperature and pH, as well as pH and time

were the most significant interactive effect on DE. Pectins that

are classed as high methoxyl (HM) have DEs values higher

than 50%. HM pectin requires a minimum amount of solu-

ble solids and a pH within a narrow range, around 2.0–3.5, in

order to formgels(Yapoet al., 2007). Most of durian rind pectin

extracted in this study showed DE value higher than 50%.

It is to note that the extraction yield was not related to DE

(Table 1). DE values of durian rind pectin producedin this study

were influenced by the extraction conditions, and the highest

DE wasobtained at extraction pHof 2.5, heating time of 1 h and

temperature of 80 ◦C, even though the yield was quite low for

these conditions. The said conditions were probably the leastharsh as compared to other conditions used, thus support-

ing the suggestion that harsh conditions of temperature and

pH could increase deesterification of polygalacturonic chain

(Mort et al., 1993). In this study, the highest yield of pectin was

achieved by using the harshest extraction conditions (90 ◦C,

4 h and pH 2.0), and this pectin had DE of ∼51% (Table 1).

Fig. 2 – Three-dimensional response surface plots for DE as a function of (a) temperature and heating time, (b) temperature

and pH and (c) pH and heating time of extraction.

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Experimental data were analyzed by factorial design to

fit the regression model mentioned in Eq.   (1).   The three-

dimensional response surface plots for yield and DE using 

Eqs.  (2) and (3)  are given in Figs. 1 and 2 showing the effect

of factors on yield and DE respectively. It can be seen that

different effect on yield and DE was exhibited by different

combination of factors. Fig. 1(a) depicts the effect of heating 

time and temperature on yield. It is clear that increasing tem-peratureand time maximizesthe yield, whilst decreasing both

or either one will result in a decrease in the yield. Onthe other

hand, Fig. 1(b) and (c)exhibited differentbehavior on yield and

can be explained in the same way.  Fig. 2 shows the behavior

of heating time, pH and temperature on DE. It is clear that

increasing temperatureand decreasing heating timeincreases

the DE ((Fig. 2(a)). Fig. 2(b) indicates that high DE pectin could

be obtained at high pH’s and low temperatures combinations,

while Fig. 2(c) shows a high DE pectin could be extracted at

high pH’s and short heating time combinations. These three-

dimensional response surface plots offer a clear picture of the

behavior of the factors on responses of the study.

4. Conclusion

The effect of time (1 and 4 h), pH (2 and 2.5) and tempera-

ture (80 and 90 ◦C) on yield and DE of durian rind pectin was

investigated.In general, durian rind pectin canbe classified as

high methoxyl type with DE higherthan50%. Yield wassignifi-

cantly affected by time, temperature and pH, and interactions

between temperature and pH, and heating time and pH. DE

was significantly affected by heating time and pH, and inter-

active effects of temperature and pH, and heating time and

pH. By considering pectin yield and DE, the acid extraction of 

durian rind pectin at 80 ◦C, for 4 h and at pH 2.5 could be suit-

able. Optimum conditions for isolation of pectin from the rind

with desired rheological and functional properties are yet to

be determined.

Acknowledgement 

Short term grant from USM (304/PTEKIND/638069), Penang is

gratefully acknowledged.

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