3 journal of food engineering volume 66 issue 2 2005

Journal of Food Engineering 66 (2005) 259–265
www.elsevier.com/locate/jfoodeng

Effect of thermal processing on the quality loss of pineapple juice
Marisa Rattanathanalerk, Naphaporn Chiewchan *, Walaiporn Srichumpoung
Department of Food Engineering, King Mongkut’s University of Technology Thonburi, Tungkru, Bangkok 10140, Thailand
Received 24 November 2003; accepted 14 March 2004

Abstract
Three indexes, namely colorimetric Hunter parameters (L, a, b and DE), hydroxymethylfurfural (HMF) and brown pigment
formation, were monitored to determine the quality loss of pineapple juice at temperatures ranging from 55 to 95 °C. The changes in
a and b values followed first order kinetics while DE fitted well to a combined model which described both non-enzymatic browning
reaction and destruction of carotenoid pigment. For browning indexes, HMF and brown pigment formation increased linearly with
heating time and could be explained using zero order reaction kinetics. The results suggested that processing temperature had a
significant effect on the color change of pineapple juice. The dependence of the rate constant on temperature was represented by an
Arrhenius equation.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Color change; Hydroxymethylfurfural; Kinetics; Non-enzymatic browning; Pineapple juice

1. Introduction
Pineapple (Ananas cosmosus) is one of the most
important commercial fruits of Thailand. The fruit can
be consumed fresh or processed in various forms and
pineapple juice is a popular product due to its very
pleasant aroma and flavor.
Thermal treatment is generally applied to extend shelf
life of fruit products. However, heating processes can
affect the quality of product which leads to consumer
dissatisfaction. Non-enzymatic browning reactions and
pigment destruction have been found to be major causes
of such problems. Therefore, kinetic studies are required

and used to predict quality degradation resulting from
process conditions.
Different methods can be used to determine the extent
of color change. Color measurement is simple and faster
than chemical analysis. The Hunter parameters (L, a, and
b) have been proven to be useful for describing visual
color change of various fruit products (Avila & Silva,
1999; Garza, Ibarz, Pag
an, & Giner, 1999; Ibarz, Pagan,
& Garza, 1999). The L value represents the light–dark
spectrum, a value is for the green–red spectrum and b

*

Corresponding author. Fax: +66-2470-9240.
E-mail address: (N. Chiewchan).

0260-8774/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jfoodeng.2004.03.016

value represents the blue–yellow spectrum (Ranganna,
1986). Other assays include the analysis of intermediates
and final products of non-enzymatic browning reactions.
The measurement of 5-hydroxymethylfurfural (HMF),
an important intermediate, is widely used as an indicator
of Maillard reactions, i.e. browning development (Bozkurt, Gogus, & Eren, 1999; Cohen, Birk, Mannheim, &
Saguy, 1998; Garza et al., 1999).
Kinetic models have been developed to evaluate
color degradation and non-enzymatic browning reactions during processing of fruit products such as apple
juice (Cohen et al., 1998), pear puree (Ibarz et al.,

1999) and peach puree (Garza et al., 1999). For pineapple products, Fontana, Howard, Criddle, Hansen,
and Wilhelmsen (1993) studied the effects of additional
components, i.e. sugars, organic acids, on the quality
deterioration kinetics of pineapple concentrate at 60–80
°C. However, information regarding the changes in
quality of pineapple drinks in terms of color change
and non-enzymatic browning during heating is
unavailable.
This work was aimed at investigating the quality loss
of pineapple juice as affected by heat treatment. Visual
color, 5-hydroxymethylfurfural (HMF) and brown pigment accumulation were monitored during heating at
55–95 °C. The kinetics of these indicators were also
investigated. The information obtained from the study


260

M. Rattanathanalerk et al. / Journal of Food Engineering 66 (2005) 259–265

could be used as a guideline for designing thermal processes to reduce the quality degradation of the products.

measured and total color differences were calculated
from L, a and b values.

2. Material and methods

2.4. Determination of non-enzymatic browning index and
5-hydroxymethylfurfural (HMF)

2.1. Preparation of pineapple juice

Fresh Smooth Cayenne pineapples were obtained
from a local market. After rinsing the fruit in tap water,
the shell and core were removed using a stainless steel
knife. The flesh was cut into small pieces and the juice
was extracted using a hydraulic machine (Sakaya Model
4104, Thailand) to extract the juice. Total soluble solid
(TSS) and pH value of the juice were determined in the
ranges of 12.2–14.2° Brix and 3.74–4.00, respectively.
The prepared juice was then kept at 4 °C until used.
2.2. Thermal treatment
A series of thin wall glass tubes (length 30 cm; inner
diameter 5 mm; wall thickness 2 mm) were filled with 8
ml of pineapple juice. The tubes (filled with the juice)
were sealed at both ends and then subjected to heat in a
water bath (Memmert Model W 600, Denmark) at 55,
65, 75, 85 and 95 °C for 80 min. The come up times for
every condition was less than 1 min. The temperature of
the juice at the center of a tube was monitored during
the experiments using type T thermocouples to an
accuracy of ±1 °C. The tubes were removed every 10
min and immediately cooled in an ice-water bath in
order to stop the heat accumulation. The control
experiments (without heat treatment) were done by the
same procedure, filling 8 ml of pineapple juice into the
tubes and placing them directly in the ice-water bath.
Color change, non-enzymatic browning index and hydroxymethylfurfural (HMF) of pineapple juice were
determined using a spectrocolorimeter (JUKI Model
JP7100/C, Japan) and spectrophotometer (Shimadzu
Model UV-2101 PC, Japan), respectively. All experiments were performed in three replicates.

The following assays were performed using the
methods as mentioned in Cohen et al. (1998). 5 ml of
95% ethyl alcohol was added to 5 ml of pineapple juice
sample. The mixture was centrifuged at 1000g for 15
min. The supernatant of the centrifuged sample was
separated into two portions. One was taken to measure
the absorbency at 420 nm for the non-enzymatic
browning index. To determine the HMF content, 2 ml
of the other portion was introduced into a 16 ml screw
cap tube. 2 ml of 12% w/w trichloroacetic acid (TCA;
Sigma, Germany) and 2 ml of 0.025 M thiobabituric
acid (TBA; Carlo Erba, Italy) were subsequently added
and mixed thoroughly. The tubes with sample were then
placed in the water bath (Memmert Model W 600,
Denmark) at 40 °C (±0.5 °C). After incubating for 50
min, the tubes were cooled immediately using tap water
and the absorbency was measured at 443 nm. A calibration curve of HMF (Aldrich, Germany) was utilized
to quantify the HMF concentration.
2.5. Experimental design
The experiments were conducted for five levels of
temperatures (55, 65, 75, 85 and 95 °C). A 2-factor
factorial design was used in scheduling of the experiments with three replicates in each case.
2.6. Data analysis
The results were reported as an average of three
replicates. Analysis of variance (ANOVA) of the two
factors and interactions were applied to the different sets
of data with a significant level of 0.05 (a ¼ 0:05).

3. Results and discussion
2.3. Color measurement

3.1. Color change of pineapple juice during heat treatment
Color changes of pineapple juice were analyzed by
measuring the transmittance using a spectrocolorimeter.
2° North skylight was used as the light source. The
spectrocolorimeter was calibrated against distilled water
(L ¼ 100, a ¼ 0, b ¼ 0) before the measurement
(according to the equipment instruction manual). A
glass cuvette (3.5 · 4 · 1.5 cm3 ) containing heat-treated
juice was placed in the cell transmittance specimen
compartment. The lid of the compartment was closed
and the analysis was then conducted. Three Hunter
parameters, namely ‘‘L’’ (lightness), ‘‘a’’ (redness and
greenness) and ‘‘b’’ (yellowness and blueness) were

The color degradation of pineapple juice as affected
by thermal processing was investigated using Hunter
parameters (L, a and b). The enzymatic browning reaction was neglected in this study as the enzymes causing
browning were susceptible to heat, at temperatures of
>50° (Martinez & Whitaker, 1995). Therefore, nonenzymatic browning and pigment destruction were
considered as the major causes of color change in
pineapple juice.
The results obtained were presented in terms of L=L0 ,
a=a0 and b=b0 when L0 , a0 and b0 represented the initial


M. Rattanathanalerk et al. / Journal of Food Engineering 66 (2005) 259–265
4.50
4.00
3.50
3.00

2.50

∆E

values once the sample temperature had reached the set
temperature. The plots between relative Hunter
parameters and processing time at different temperatures are shown in Figs. 1–4. In order to explain the
phenomena of color change in pineapple juice, the data

261

2.00
1.50
1.00

1.04

0.50

1.02

0.00
0

1.00

L/L0

10

20

30

40

50

60

70

80

90

Heating time (min)

0.98
0.96

Fig. 4. The change of total color different (DE) of pineapple juice
samples at different heating temperatures: 55 °C ðrÞ, 65 °C (h), 75 °C
(m), 85 °C (s) and 95 °C (d).

0.94
0.92
0.90
0.88
0.86

0.84
0

10

20

30

40

50

60

70

80

90

Heating time (min)

Fig. 1. The change of lightness ðL=L0 Þ of pineapple juice samples at
different heating temperatures: 55 °C ðrÞ, 65 °C (h), 75 °C (m), 85 °C
(s) and 95 °C (d).

1.25

a/ao

1.20
1.15
1.10
1.05
1.00

0

10

20

30

40
50
60
Heating time (min)

70

80

90

Fig. 2. The change of redness ða=a0 Þ of pineapple juice samples at
different heating temperatures: 55 °C ðrÞ, 65 °C (h), 75 °C (m), 85 °C
(s) and 95 °C (d).

1.00

b/bo

0.96
0.92
0.88
0.84
0.80
0

10

20

30

40

50

60

70

80

Heating time (min)

Fig. 3. The change of yellowness ðb=b0 Þ of pineapple juice samples at

different heating temperatures: 55 °C ðrÞ, 65 °C (h), 75 °C (m), 85 °C
(s) and 95 °C (d).

were fitted using a kinetic model and kinetic rate constants are presented in Table 1.
Fig. 1 shows the change in relative L values during
heat treatment under various conditions. With
increasing temperature and time, pineapple juice became darker which corresponded to a decrease in L
value. Most of the previous works demonstrated that
the changes in L value as affected by heat treatment
followed first order kinetics (Avila & Silva, 1999;
Garza et al., 1999; Ibarz et al., 1999). Moreover, two
consecutive first order reactions have been proposed
when the experimental data could not be described by
single reaction (Barreiro, Milano, & Sandoval, 1997).
However, it was obvious that the changes in L value
found in the present study could not be fitted to any
simple kinetic model. The degradation in L value might
be influenced by an increase in a value and a decrease
in b value. The results suggested that the reduction in
the luminosity were not from a single mechanism.
Therefore, the kinetics for describing L value was not
determined.
The evolution of an a parameter with treatment time
can be fitted to both zero and first order reactions (Fig.
2). However, with increasing temperature, the experimental data were better fitted to first order kinetics. This
finding was consistent with many previous studies (Avila
& Silva, 1999; Garza et al., 1999; Ibarz et al., 1999). The
values of the kinetic constants increased with treatment
temperature. This supported the theory that an increase
in heating temperature induced the color shift to red.

Since the major color of pineapple juice is yellow, the
amount of this pigment in pineapple flesh is an excellent
measure of quality (Mehrlich & Felton, 1980). In this
study, the b value was used as an indicator to describe
the pigment destruction in the juice. Fig. 3 shows that
the first order kinetic model fitted well to parameter b
which was consistent with previous works (Avila &
Silva, 1999; Barreiro et al., 1997). The rate constant


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Table 1
Kinetic parameters for color change of pineapple juice
k0 (minÀ1 ) · 103

k1 (minÀ1 ) · 103

R2

Parameter

Kinetic model

T (°C)

a=a0

n¼1

55
65
75
85
95

0.50
0.83
1.41
1.79
2.40

0.980
0.950
0.962
0.992
0.972

b=b0

n¼1

55
65
75
85
95

0.52
0.91
1.40
1.87
2.40

0.958
0.996
0.987
0.990
0.985

DE

Combined

55
65
75
85
95

25.31
31.64
31.34
46.39
59.96

0.963
0.968

0.996
0.991
0.982

28.73
69.72
81.03
132.31
219.47

increased with the higher heating temperatures. This
could be explained by the assumption that high temperature accelerated the carotenoid isomerization which
led to the loss of yellowness (Chen, Peng, & Chen, 1995;
Singleton, Gortner, & Young, 1961).
Previous studies of the color change during heat
treatment showed similar results. Avila and Silva (1999)
examined the color degradation of peach puree as affected by heat treatment. Peach puree became darker,
corresponding to a decrease in L value and an increase in
a value, with increasing temperature. Moreover, the loss
of yellowness was also expressed by a decrease in the b
value. They concluded that the major causes of color
change were due to carotenoid degradation and nonenzymatic browning (Maillard).
To describe the total color of pineapple juice, the
combination of parameters L, a and b, were determined
in terms of total color difference (DE). DE of pineapple
juice sample was calculated using Eq. (1):
2

2

2 1=2

DE ¼ ½ðDLÞ þ ðDaÞ þ ðDbÞ Š

ð1Þ

The plot between the total color difference of pineapple juice and time is shown in Fig. 4. The results
showed that DE increased significantly at higher heating
temperatures and prolonged processing times. It was
also observed that the first portion of the curves exhibited steeper slopes as the heating temperature increased.
It means that higher temperature accelerated the
chemical reactions and most of the color change occurred during the early heating period. To describe the
reactions closely, the juice samples may be taken more
frequently at higher heating temperatures.
In this current study, the change in DE did not fit
simple zero or first order kinetic models. Color changes
of pineapple juice may be the result of more than one
reaction and these reactions may not occur simultaneously at one temperature. Therefore, temperature was

an important driving force behind the changes in the
color of heated samples. The results suggested that the
change in DE was influenced by both non-enzymatic
browning and pigment destruction. The combined
model was applied to describe the phenomena which
occurred during heating of pineapple juice.
The combined model was used widely to explain the
color change in many fruit products (Avila & Silva,
1999; Garza et al., 1999; Ibarz et al., 1999; Lozano &
Ibarz, 1997) and was proposed as a two-stage mechanism (Ibarz et al., 1999). The first stage is color formation due to the Maillard reaction which follows a zero
order kinetics ðk0 Þ. The second stage is destruction of

natural fruit pigments which follow first order kinetics
ðk1 Þ. The combined kinetic model is shown in Eq. (2):
C ¼ Kc À ðKc À C0 Þ expðÀk1 tÞ

ð2Þ

Substituting C with DE and DE at initial time is zero
(C0 ¼ 0), Eq. (2) becomes
DE ¼ Kc ½1 À expðÀk1 tފ

ð3Þ

where Kc ¼ k0 =k1 .
In this work, the results showed that the two reactions occurred at a higher rate as temperature increased.
Kc represents the relation between kinetic constants, k0
(color formation) and k1 (pigment destruction). Kc values greater than 1 indicated that the Maillard reaction
predominated over pigment destruction. Moreover, the
higher the temperature, the higher the value of Kc . This
suggested that reaction rates were strongly dependent on
processing temperatures.
Many studies of the color changes during heat
treatment of fruit puree demonstrated similar finding.
Ibarz et al. (1999) found that a combined model could
be used to describe the change of DE in pear puree. The
Maillard reaction was found to be dominant rather than
pigment destruction. Garza et al. (1999) implied that DE


M. Rattanathanalerk et al. / Journal of Food Engineering 66 (2005) 259–265

263

Table 2
Arrhenius equation parameters for the different variables of pineapple juice

a=a0
b=b0
DE

Kinetic model
n¼1
n¼1
Combined; n ¼ 0

K0
2

11.46 · 10
9.67 · 102
1.12 · 105

fitted to combined kinetic model and stated that brown
color formation was higher than pigment destruction in
peach puree.
The variation in kinetic constants with heating temperature could be described using the Arrhenius relationship. The constant parameters obtained from the
Arrhenius equation are given in Table 2. In this study, a,
b and DE values were chosen to demonstrate the change
of pineapple juice color during heating. Activation energy values of 39.78, 39.20 and 47.33 kJ/mol were obtained for parameters a, b and DE, respectively. These
values were found to be lower than those reported in the
literature for peach puree (Avila & Silva, 1999; Ibarz

et al., 1999) and pear puree (Garza et al., 1999). This
could be due to the different type of fruit, which implied
the differences in composition such as sugar and amino
acid content, total solid content, pH, acidity and also the
temperature range of the study (Beveridge & Harrison,
1984; Ahmed, Shivhare, & Kaur, 2002). This was supported by the work of Lozano and Ibarz (1997). Above
authors indicated that change in hue during heating was
different for each fruit pulp. For example, apple pulp was
more sensitive to discoloration during heating than plum
pulp. Therefore, the composition of the products was
related to different degrees of heat sensitivity.
3.2. 5-Hydroxymethylfurfural (HMF) accumulation and
brown pigment formation in pineapple juice during heat
treatment
As non-enzymatic browning is one of the major
causes of color change in fruit products, the effect of
heating temperature and processing time on the accumulation of HMF and brown pigment formation were

Ea (kJ/mol)

R2

39.788
39.201
47.336

0.983
0.978
0.962

2.00

1.80

HMT / HMT o

Variable

1.60

1.40

1.20

1.00
0

10

20

30

40

50

60

70

80

90

Heating time (min)

Fig. 5. The relative value of HMF of pineapple juice samples at different heating temperatures: 55 °C ðrÞ, 65 °C (h), 75 °C (m), 85 °C
(s) and 95 °C (d).

investigated in this study. The relationship between
relative HMF content ðHMF=HMF0 Þ and processing
time at different temperatures applied is shown in Fig. 5.
It was observed that heating temperature had a marked
effect on the formation of HMF. The results indicated
that HMF increased linearly with time and the higher
amounts were found at the higher heating conditions.
The relationship between relative A420 ðA420 =A0420 Þ and
time was also observed to be linear, similar to HMF
development. Therefore, zero order kinetics was applied
to describe the change of both substances and the
equation used is shown as:
C ¼ C0 þ k0 t

ð4Þ

Table 3 shows the values of the kinetic parameters
for HMF and brown pigment formation. The kinetic
constants tended to increase with the processing

Table 3
Kinetic parameters for HMF evolution and brown pigment formation of pineapple juice
Parameter

Kinetic model

T (°C)

k0 (minÀ1 ) · 103

R2

HMF=HMF0

n¼0

55
65
75
85
95

3.80
5.07
6.76
9.14
12.26

0.971
0.992

0.982
0.989
0.990

A420 =A0420

n¼0

55
65
75
85
95

0.10
0.19
0.31
0.41
0.56

0.973
0.956
0.973
0.988
0.982


264

M. Rattanathanalerk et al. / Journal of Food Engineering 66 (2005) 259–265

Table 4
Arrhenius parameters for the different variables of pineapple juice
Variable

Kinetic model

K0

Ea (kJ/mol)

R2

HMF=HMF0
A420 =A0420

n¼0
n¼0

179.182
724.95

29.401
42.794

0.998
0.977

temperature. This indicated that HMF was formed at a
higher rate at elevated temperatures and subsequently

this phenomenon affected brown pigment formation.
Several works studied the Maillard reaction in
aqueous systems containing glucose and amino acid
(Carabasa-Giribet & Ibarz-Ribas, 2000; Gogus, Bozkurt, & Eren, 1998; Reyes, Poocharoen, & Wrolstad,
1982). Garza et al. (1999) reported that the HMF content increased with treatment time. This increase occurred from with disappearance of the sucrose due to
Maillard reaction and sucrose hydrolysis increased with
treatment temperature. Pineapple juice typically contains sucrose, glucose and fructose (C
amara, Dıez, &
Torija, 1995) which are the substrates of the Maillard
reaction. When the temperature increased, the sucrose in
the juice was easily hydrolyzed and more glucose and
fructose were formed, and thus increased the substrates
of the Maillard reaction. Moreover, the high temperature accelerated the reaction which is shown by the increase in rate constant values.
The change in the relative absorbancy at 420 nm
ðA420 =A0420 Þ which is related to brown pigment formation
was adequately described by zero order kinetics with the
high correlation coefficient ðR2 > 0:95Þ. The results obtained from this study were consistent with previous
works. Beveridge and Harrison (1984) studied the effect
of temperature (50–80 °C) and soluble solids (45.2–72.5°
Bx) on non-enzymatic browning in pear juice concentrate and browning could be modeled as a zero order
rate process. Cohen et al. (1998) reported that the zero
order kinetics could be used as a non-enzymatic
browning index ðA420 Þ for apple juice (13° Bx) heating at
95–123 °C.
Comparing the activation energy obtained for
HMF=HMF0 to A420 =A0420 it was observed that the activation energy found for HMF formation was lower than
that of brown pigment formation. The results implied
that HMF occurred at a higher rate than the latter substance. After heating, HMF retained in the juice would
change to a brown pigment during storage. Therefore,
HMF was proposed as a useful indicator to determine

the change of color in the pineapple juice (Table 4).

4. Conclusions
The quality degradation of pineapple juice due to heat
treatment was studied at temperatures ranging from 55

to 95 °C. The changes in Hunter parameters a and b
followed first order kinetics while the change in parameter L could not be fitted to any simple relationship.
Total color difference ðDEÞ could be described using a
combined model which included the effect of both nonenzymatic browning and pigment destruction. The
changes of 5-hydroxymethylfurfural (HMF) and brown
pigment formation were chosen to demonstrate the nonenzymatic browning reaction occurring during the study
and were found to follow zero order kinetics. The results
suggested that processing temperatures strongly influenced the reaction rate. The Arrhenius model could be
used to describe the temperature dependence of the
reaction rate constant for all parameters considered. A
study of quality loss in terms of sugars and amino acids,
the substrates of the Maillard reaction, together with
carotenoid destruction as affected by heat treatment is
recommended for future work.

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