Effect of thermal processing on the quality loss of pineapple juiceDepartment of Food Engineering, King Mongkut’s University of Technology Thonburi, Tungkru, Bangkok 10140, Thailand Recei
Trang 1Effect of thermal processing on the quality loss of pineapple juice
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 95C The changes in
aand 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
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, Pagan, & Giner, 1999; Ibarz, Pagan,
& Garza, 1999) The L value represents the light–dark
spectrum, a value is for the green–red spectrum and b
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 (Bo-zkurt, 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 reac-tions 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 pine-apple 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 pig-ment accumulation were monitored during heating at 55–95 C The kinetics of these indicators were also investigated The information obtained from the study
* Corresponding author Fax: +66-2470-9240.
E-mail address: naphaporn.rat@kmutt.ac.th (N Chiewchan).
Journal of Food Engineering 66 (2005) 259–265
www.elsevier.com/locate/jfoodeng
0260-8774/$ - see front matter 2004 Elsevier Ltd All rights reserved.
doi:10.1016/j.jfoodeng.2004.03.016
Trang 2could be used as a guideline for designing thermal
pro-cesses to reduce the quality degradation of the products
2 Material and methods
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 4C 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 95C 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
hy-droxymethylfurfural (HMF) of pineapple juice were
determined using a spectrocolorimeter (JUKI Model
JP7100/C, Japan) and spectrophotometer (Shimadzu
Model UV-2101 PC, Japan), respectively All
experi-ments were performed in three replicates
2.3 Color measurement
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
(L¼ 100, a¼ 0, b¼ 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
measured and total color differences were calculated from L, a and b values
2.4 Determination of non-enzymatic browning index and 5-hydroxymethylfurfural (HMF)
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 cali-bration 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 experi-ments 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 (a¼ 0:05)
3 Results and discussion 3.1 Color change of pineapple juice during heat treatment The color degradation of pineapple juice as affected
by thermal processing was investigated using Hunter parameters (L, a and b) The enzymatic browning reac-tion was neglected in this study as the enzymes causing browning were susceptible to heat, at temperatures of
>50 (Martinez & Whitaker, 1995) Therefore, non-enzymatic 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=a and b=b when L, a and b represented the initial
260 M Rattanathanalerk et al / Journal of Food Engineering 66 (2005) 259–265
Trang 3values once the sample temperature had reached the set
temperature The plots between relative Hunter
parameters and processing time at different
tempera-tures are shown in Figs 1–4 In order to explain the
phenomena of color change in pineapple juice, the data
were fitted using a kinetic model and kinetic rate con-stants 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 be-came 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 experi-mental 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
0.84
0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
1.02
1.04
Heating time (min)
Fig 1 The change of lightness ðL=L 0 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
1.05
1.10
1.15
1.20
1.25
Heating time (min)
Fig 2 The change of redness ða=a 0 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).
0.80
0.84
0.88
0.92
0.96
1.00
Heating time (min)
Fig 3 The change of yellowness ðb=b 0 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).
0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50
90 Heating time (min)
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).
M Rattanathanalerk et al / Journal of Food Engineering 66 (2005) 259–265 261
Trang 4increased with the higher heating temperatures This
could be explained by the assumption that high
tem-perature 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
af-fected by heat treatment Peach puree became darker,
corresponding to a decrease in L value and an increase in
avalue, 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
non-enzymatic 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):
DE¼ ½ðDLÞ2þ ðDaÞ2þ ðDbÞ21=2 ð1Þ
The plot between the total color difference of
pine-apple 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
exhib-ited steeper slopes as the heating temperature increased
It means that higher temperature accelerated the
chemical reactions and most of the color change
oc-curred 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
simulta-neously 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 mecha-nism (Ibarz et al., 1999) The first stage is color forma-tion due to the Maillard reacforma-tion which follows a zero order kinetics ðk0Þ The second stage is destruction of natural fruit pigments which follow first order kinetics
ðk1Þ The combined kinetic model is shown in Eq (2):
C¼ Kc ðKc C0Þ expðk1tÞ ð2Þ Substituting C with DE and DE at initial time is zero (C0¼ 0), Eq (2) becomes
DE¼ Kc½1 expðk1tÞ ð3Þ where Kc ¼ k0=k1
In this work, the results showed that the two reac-tions occurred at a higher rate as temperature increased
Kc represents the relation between kinetic constants, k0
(color formation) and k1 (pigment destruction) Kc val-ues 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
Table 1
Kinetic parameters for color change of pineapple juice
262 M Rattanathanalerk et al / Journal of Food Engineering 66 (2005) 259–265
Trang 5fitted 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
tem-perature could be described using the Arrhenius
rela-tionship The constant parameters obtained from the
Arrhenius equation are given in Table 2 In this study, a,
band DE values were chosen to demonstrate the change
of pineapple juice color during heating Activation
en-ergy values of 39.78, 39.20 and 47.33 kJ/mol were
ob-tained 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
sup-ported 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
accu-mulation of HMF and brown pigment formation were
investigated in this study The relationship between relative HMF content ðHMF=HMF0Þ 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=A0
420Þ 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:
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
A 420 =A 0
Table 2
Arrhenius equation parameters for the different variables of pineapple juice
1.00 1.20 1.40 1.60 1.80 2.00
Heating time (min)
Fig 5 The relative value of HMF of pineapple juice samples at dif-ferent heating temperatures: 55 C ðrÞ, 65 C (h), 75 C (m), 85 C (s) and 95 C (d).
M Rattanathanalerk et al / Journal of Food Engineering 66 (2005) 259–265 263
Trang 6temperature 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,
Bo-zkurt, & Eren, 1998; Reyes, Poocharoen, & Wrolstad,
1982) Garza et al (1999) reported that the HMF
con-tent increased with treatment time This increase
oc-curred from with disappearance of the sucrose due to
Maillard reaction and sucrose hydrolysis increased with
treatment temperature Pineapple juice typically
con-tains sucrose, glucose and fructose (Camara, 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
tempera-ture accelerated the reaction which is shown by the
in-crease in rate constant values
The change in the relative absorbancy at 420 nm
ðA420=A0
420Þ which is related to brown pigment formation
was adequately described by zero order kinetics with the
high correlation coefficientðR2>0:95Þ The results
ob-tained from this study were consistent with previous
works Beveridge and Harrison (1984) studied the effect
of temperature (50–80C) and soluble solids (45.2–72.5
Bx) on non-enzymatic browning in pear juice
concen-trate 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 indexðA420Þ for apple juice (13 Bx) heating at
95–123C
Comparing the activation energy obtained for
HMF=HMF0to A420=A0
420it was observed that the acti-vation 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
sub-stance 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 para-meter 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 non-enzymatic browning and pigment destruction The changes of 5-hydroxymethylfurfural (HMF) and brown pigment formation were chosen to demonstrate the non-enzymatic browning reaction occurring during the study and were found to follow zero order kinetics The results suggested that processing temperatures strongly influ-enced 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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