The effect of high pressure treatment on rheological characteristics and colour of mango pulp

Original article

The effect of high pressure treatment on rheological

characteristics and colour of mango pulp

Jasim Ahmed,* Hosahalli S. Ramaswamy & Nikhil Hiremath

Department of Food Science & Agricultural Chemistry, Macdonald Campus of McGill University, Ste. Anne de Bellevue,

PQ, Canada H9X 3V9

(Received 15 December 2003; Accepted in revised form 1 March 2005)

Summary The effect of high-pressure (HP) treatment (100–400 MPa for 15 or 30 min at 20 �C) on the

rheological characteristics and colour of fresh and canned mango pulps was evaluated.

Differences were observed in the rheological behaviour of fresh and canned mango pulps

treated with HP. Shear stress–shear rate data of pulps were well described by the Herschel–

Bulkley model. The consistency index (K) of fresh pulp increased with pressure level from

100 to 200 MPa while a steady decrease was noticed for canned pulp. For fresh pulp the

flow behaviour index decreased with pressure treatment whereas an increasing trend was

observed with canned pulp. Storage and loss moduli of treated fresh pulp with HP

increased linearly with angular frequency up to 200 MPa for a treatment time of 30 min

while a steady decreasing trend was found for processed pulp. No significant variation in

colour was observed during pressure treatment.

Keywords Consistency coefficient, dynamic rheology, elastic modulus, flow behaviour, glass transition temperature,

total colour difference, viscous modulus, yield stress.

Introduction

Mango (Magnifera indica L.) is one of the

important tropical fruits. It is usually considered

as a high quality fruit and has been recognized as

�king of the fruits� in the Orient. The fruit is

relished for its succulence, exotic flavour and

delicious taste. Mango is a rich source of carot-

enoids and provides high vitamin A content (Pott

et al., 2003). The fruit has tremendous potential

for processing and export. However, substantial

quantities of the fruits are wasted because of poor

post-harvest management and lack of appropriate

processing facilities in developing countries. Some

mango varieties like Alphonso, Duseheri, Chousa,

Baganpalli and Langra experience excellent con-

sumer demand when the fruits are marketed in the

fresh form. Mango fruit is also processed and then

marketed in various forms. Mango pulp and puree

are the most popular mango products and are

generally preserved as canned product by subject-

ing fruit to thermal processing. This extends the

year round availability of mango (Shrikhande

et al., 1976). The pulp is used to manufacture

beverages, ice-cream, mango leather and other

products. For such processed foods to be of

consistent quality with technically and economic-

ally feasible processes, it is imperative that the

physico-chemical properties of the pulp are docu-

mented and standardized. These properties include

colour, flavour and texture (rheological proper-

ties) and they are of primary importance from the

quality and processing point of view.

High pressure (HP) processing is a novel tech-

nique in which a food experiences an elevated

pressure in a quasi-instantaneous manner

throughout the mass (Cheftel, 1995). HP process-

ing has successfully been used for various specialty

foods and numerous reports are available on its

application to food (Oxen & Knorr, 1993; Van

Camp & Huyghebaert, 1995; Basak & Rama-

swamy, 1997, 1998; Mussa et al., 1999; Hsu & Ko,

2001; Ahmed & Ramaswamy, 2003). The process*Correspondent: Fax: 1 514 398 7977;

e-mail: [email protected]

International Journal of Food Science and Technology 2005, 40, 885–895 885

doi:10.1111/j.1365-2621.2005.01026.x

� 2005 Institute of Food Science and Technology Trust Fund

has been considered as being either alternative or

complimentary to thermal processing. HP proces-

sing retains the sensory qualities of the food better

as compared with thermal processing (Hayakawa

et al., 1994). HP processing has been successfully

applied to various fruit products, giving better

quality retention of colour, flavour and vitamins

(Smelt, 1998) than thermal processing; however

changes in texture are caused by the process

(Prestamo & Arroyo, 1998). A few fruit products

treated with HP such as juices and jams have been

commercialized in some developed countries.

However, the success of the process depends on

the inactivation of enzymes and destruction of

microorganisms to a safe level.

Understanding the rheological properties of

food products is important for product develop-

ment. In particular these properties influence

design and evaluation of process equipment such

as pumps, piping, heat exchangers, evaporators,

sterilizers and mixers. Knowledge of the funda-

mental rheological properties of any food can be an

indication of how the food is going to behave under

various processing conditions. Numerous studies

have been conducted on the rheological properties

of fruit pulp, purees and paste (Rao, 1977; Ibarz

et al., 1995; Bhattacharya, 1999; Ahmed &

Ramaswamy, 2004). The various factors affecting

the rheological behaviour of fruit purees and

concentrates include temperature (Holdsworth,

1971; Vitali & Rao, 1984; Oomah et al., 1999),

total soluble solids (TSS)/concentration (Harper &

El-Sahrigi, 1965; Ilicali, 1985), particle size (Tan-

glertpaibul & Rao, 1987; Pelegrine et al., 2002),

addition of enzyme (Khalil et al., 1989; Bhatta-

charya & Rastogi, 1998) and pH (Dik & Ozilgen,

1994). Rheology of mango pulp and concentrate

have been studied by various researchers (Manohar

et al., 1990; Bhattacharya, 1999; Pelegrine et al.,

2002) and results found have not always been

consistent. Most researchers have reported that

yield stress does not exist, the exception being

Bhattacharya (1999). However, no information is

available on the effect of HP on the rheology of

fresh and/or processed mango pulp.

With the advent of controlled stress/rate rheom-

eters, it has become convenient to study the

rheological characteristics of fruit pulp/puree under

a wide range of conditions. Those instruments have

a wide range of measurement capabilities from very

low to extremely high shear rate and extreme

sensitivity. Tests can also be set under steady,

dynamic or oscillatory shear.Most previous reports

on the rheology of fruit puree are based on

experiments using a high shear rate, whereas in

actuality low and medium shear rates are of greater

industrial significance, especially during mixing or

product development when there is a smaller degree

of structural breakdown. Therefore, rheological

studies based on low and medium shear rates are of

much more practical significance.

Another important characteristic of fruit

purees/paste is the yield stress, which indicates

the threshold stress to initiate the flow. The new

generation of rheometers have been equipped with

low shear measurement and data analysis software

that routinely calculates yield stress and rheolog-

ical parameters.

The colour of mango pulp is capusine yellow or

reddish and carotenoids contribute to the mango

colour. The b-carotene constituent is the major

pigment (50–64%) of the ripe mango (John et al.,

1970). The maintenance of naturally coloured

pigments in thermally processed and stored food

is a major challenge in food processing. Ahmed

et al. (2002) have studied the degradation of the

colour of mango puree during thermal processing

and they reported that colour degradation fol-

lowed first-order reaction kinetics. However, pres-

sure affects colour differently. It has been reported

that HP causes an increased browning reaction in

some vegetable products (Eshtiagi & Knorr, 1993;

Arrayo et al., 1997), while Fernandez et al. (2001)

reported no effect of pressurization on pigments of

tomato puree. No reports are available on the

colour of mango puree during HP treatment.

The objective of the present work was to study

the effect of high-hydrostatic pressure on flow and

dynamic rheological characteristics as well as the

visual colour of mango puree. This information

will enable better understanding of how mango

pulps respond to high hydrostatic pressure.

Materials and methods

Mango pulp

Fresh mangoes (Cv. Chousa) were procured from

a local store. The mangoes were produce of

Pakistan and were airlifted to Canada. The

Pressure rheology and colour of mango pulp J. Ahmed et al.886

International Journal of Food Science and Technology 2005, 40, 885–895 � 2005 Institute of Food Science and Technology Trust Fund

mangoes were thoroughly washed, peeled and the

pulp portion was sliced to separate the stone, all

operations were done manually. The slices were

put through a fruit strainer with a screen of 1 mm

clearance to get mango pulp of uniform consis-

tency and particle size. The pulp was immediately

frozen and stored at )20 �C for a maximum of

3 days prior to subjecting it HP treatment.

Another lot of canned mango pulp of Indian

origin (Cv Alphanso; Cedar brand marketed by

Phoenica Products Inc. Montreal, Canada, canned

in 2002) was purchased from a local store.

High hydrostatic pressure treatment

An isostatic HP machine unit (Model# CIP 42260;

ABB Autoclave System, Columbus, OH, USA)

with a chamber dimension of 0.56 m height and

0.1 m diameter was used to give HP treatment.

Distilled water containing 2% water soluble oil

(Part No. 5019; Autoclave Engineers, Columbus,

OH, USA) was used as the pressure medium for

pressurization. A smooth pressure rise of

2.4 MPa s)1, after an initial delay of 15 s, was

characteristic of the equipment pressurization. The

come-up time for pressurization ranged from 33 s

to 2.8 min depending upon the pressure level and

the depressurization time was �10 s. Test samples

were treated at 100, 200, 300 and 400 MPa for 15

and 30 min. The chamber temperature was regu-

lated at 20 (±1.5) �C by circulating cold water.

The fruit temperature was recorded by a thermo-

couple (K-type) connected to a data logger during

the experimentation. Pressure treatment time

mentioned in the results does not include the

pressure build up or release times.

Prior to treatment, samples in sealed test pou-

ches were thawed and/or equilibrated to the

desired temperature (approximately 8–17 �Cdepending on the pressure level) to accommodate

the adiabatic heating of samples, which was about

3C/100 MPa. They were then placed inside the HP

vessel submerged in water. Cold water just below

the desired temperature was circulated through the

jacket during the entire duration of the experi-

mental runs. Duplicate samples were used for each

pressure treatment. The pressure treated pouches

were immediately transferred to a refrigerator

(4–6 �C) and subsequently the colour and rheo-

logy were evaluated.

Rheological measurement

Rheological measurements (oscillation and flow

both) were made in a controlled shear rate

rheometer (AR 2000; TA Instruments, New Cas-

tle, DE, USA) with its accompanying computer

software (Rheology Advantage Data Analysis

Program, TA). The sample was placed between

parallel-plate geometry (60 mm diameter) and

measurements were made using a gap size set at

1 mm. The AR 2000 Concentric Cylinder System

is based on an efficient method of peltier tempera-

ture control and temperature could thus be

efficiently monitored during the experiments. For

both steady flow and dynamic rheological studies

a sample of approximately 3 mL was placed

between the plates and measurements were made

at 20 �C.The instrument was programmed to maintain a

set temperature for equilibration for 15 min fol-

lowed by a two-cycle shear in which the shear rate

was increased linearly from 0.1 to 100 s)1 in 5 min

and immediately decreased from 100 to 0.1 s)1 in

the next 5 min. All the rheological parameters

were obtained from the software (Rheology

Advantage, TA version 2.3, TA Instruments,

New Castle, DE, USA). In order to perform a

quantitative comparison of samples various rheo-

logical flow models based on shear stress–shear

rate were tested (Newtonian, Bingham, Casson,

power law, Herschel Bulkley) and the best fit

model was selected on the basis of standard error,

which is defined as:

XðXm � XcÞ2=ðn� 2Þh i0:5

=Range� 1000 ð1Þ

Where Xm is the measured value; Xc is the

calculated value; n is the number of data points

and the range is the maximum value of Xm – the

minimum value.

For dynamic rheological studies, the linear

viscoelastic range was tested and the oscillation

stress was selected, it was based on the linear part

of the viscoelastic range. Measurements were made

during two cycles of the frequency sweep (0.1–

10 Hz and back) at 20 �C after an equilibration

period of 15 min. Dynamic rheological parameters

storage modulus (G¢), loss modulus (G¢¢) were

obtained directly from the instrument software.

All rheological experiments were in duplicate.

Pressure rheology and colour of mango pulp J. Ahmed et al. 887

� 2005 Institute of Food Science and Technology Trust Fund International Journal of Food Science and Technology 2005, 40, 885–895

Physio-chemical characteristics

Visual colour was measured using a Minolta

reflectance colorimeter (Minolta Corp, Ramsey,

NJ, USA) in terms of L (lightness), a (redness and

greenness) and b (yellowness and blueness). The

colorimeter was calibrated with a white standard.

A glass petri dish containing the pressure-treated

puree was placed below the light source and post-

process colour L, a, b values were recorded. L, a

and b measurements were evaluated from three

samples and the values were averaged. A numer-

ical total colour difference (DE), hue (H) and

chroma (C) were calculated as:

DE ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðL0 � LÞ2 þ ða0 � aÞ2 þ ðb0 � bÞ2

q

C ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffia2 þ b2

pand h ¼ tan�1ðb=aÞ

where, L0, a0 and b0 represented the readings of

the control sample, and L, a and b represented the

individual readings after HP treatment.

The TSS and pH of both mango purees were

determined by a refractrometer (Atago, Japan)

and pH-meter (Accumet, USA) respectively. Pro-

ximate composition of both pulps was analysed as

per the method described by AOAC (1980).

Differential scanning calorimetry

The glass transition temperature (Tg) of mango

pulp samples was determined using a TA Q100

Differential Scanning Calorimeter (DSC) (TA

Instruments, New Castle, DE, USA), equipped

with a refrigerated cooling system that efficiently

monitored temperature to )90 �C. Nitrogen was

used as purge gas at a flow rate of 50 mL min)1.

Hermetic sealed aluminium pans were used to

avoid any moisture loss during the analysis. In the

experiment, mango pulps were sealed, cooled to

)90 �C, held for 15 min and then warmed to

10 �C at a heating rate of 5 �C min)1; equilibrated

to 10 �C, held for 15 min and finally cooled to

)90 �C at 5 �C min)1. A four axis robotic device

automatically loaded the sample and reference

pans of the DSC. An empty aluminium pan was

used as a reference. Rescans were done immedi-

ately to confirm the existence of a Tg.

The DSC measurement was done in duplicate.

The DSC data were analysed with the Universal

Analysis Software (version 3.6C) for thermal

analysis, which was provided with the instrument

(TA Instruments, Newcastle, NJ, USA). Tg is a

second order transition and was recognized as a

change of heat flow step in the DSC thermograms

(Roos, 1995). Midpoint Tg was obtained from the

Universal Analysis (TA Instruments) software.

Statistical analysis

The influence of residence time and pressure level

applied on mango pulp was determined by paired

samples t-test using the Microsoft Excel software

(Microsoft Office Excel, Microsoft Corporation,

USA). Significance of differences was defined at

P £ 0.05.

Results and discussion

Unprocessed control mango pulps

Untreated (pressure) pulp was evaluated initially to

serve as a control point for rheological and colour

changes of the HP-treated pulps. The chemical and

physical properties (mean ± 1 SD) of Chousa and

Alphanso pulps evaluated prior to HP treatment

were: pH 5.15 ± 0.02, 23.12 ± 0.03 �Brix and

4.01 ± 0.03, 27.1 ± 0.02 �Brix, and L, a and b

values (54.23 ± 0.19, 8.49 ± 0.51, 33.28 ± 0.98

and 51.05 ± 0.15, 14.32 ± 0.10, 39.69 ± 0.33)

respectively. The average proximate compositions

of pulps of Chousa and Alphanso were: moisture,

72.18 ± 0.12 and 68.8 ± 0.08%; protein;

0.71 ± 0.04 and 0.61 ± 0.07%; fat, 0.27 ± 0.02

and 0.52 ± 0.05%; ash, 0.44 ± 0.04 and

0.38 ± 0.09%; crude fibre, 1.27 ± 0.03 and

0.87 ± 0.02%; and carbohydrate, 25.13 ± 0.04

and 28.82 ± 0.07%. The starch contents were

2.4 ± 0.07 and 1.84 ± 0.06% for Chousa and

Alphanso pulps, respectively. The pH of Alphanso

mango pulps was low because of acidification for

shelf-stability. The TSS and pH of test samples

remained unchanged after the HP treatment.

Rheological properties

Flow models

Various flow rheological models (Newtonian,

Casson, Bingham, power and Herschel-Bulkley)

were tested to see which best described the data for



shear stress–shear rate of control and mango pulp

treated by pressure. It was observed that the

Herschel Bulkley model was the best model based

on estimated errors (Table 1). For all test cases,

the magnitudes of standard errors were always

<20 which was satisfactory. The Herschel Bulkley

model is represented as:

r ¼ r0 þ KðcÞn ð2Þ

where r is the shear stress (Pa), r0 is the yield

stress, c is the shear rate (s)1), K is the consistency

coefficient (Pa sn) and n is the flow behaviour

index (dimensionless).

This model was recommended by Bhattacharya

(1999) for describing the flow curves of mango pulp

(TSS of 16�Brix) while Pelegrine et al. (2002) foundthat the Mizrahi–Berk model well described the

rheograms of mango pulp with a TSS of 13.3�Brix.

Effect of high pressure on flow characteristics of

mango pulp

The rheograms for both Chousa and Alphanso

mango pulps are shown in Fig. 1a and b respect-

ively. The control was a sample without pressure

treatment. Both pulps exhibited pseudoplasticity

with the presence of a yield stress. The rheological

parameters are presented in Table 2 for Chousa

and Alphanso pulps, respectively.

Yield stress is one of the important quality

parameters that characterize the properties of

semi-solid foods. The magnitude of yield stress

for Alphansomango pulp ranged between 3.81 and

6.24 Pa while for Chousa the magnitude varied

from 1.09 to 6.14 Pa as a result of the HP

treatment. The yield stress consistently increased

with pressure for Alphanso pulp and followed a

linear relationship (Eqn 3). However, no

consistent trend was found for Chousa pulp.

Bhattacharya (1999) observed a yield stress for

Totapuri mango pulp to range between 2.7 and

3.6 Pa at 5–30 �C.

so ¼ 0:006Pþ 3:61ðR2 ¼ 0:95and SE ¼ 0:26Þð3Þ

The HP treatment resulted in an increase in

shear stress of Chousa pulp at any shear rate

(Fig. 1a) while a reverse trend was observed for

Alphanso pulp (Fig. 1b). It was observed that the

Table 1 Fitting of various flow

models for Chousa mango pulp at

400 MPa for 30 minNo. Model

Yield

(Pa)

Consistency

coefficient

(Pa sn)

Flow

behaviour

index ()) SE

1 Newtonian model – 0.744* – 303.7

2 Power law model – 15.73 0.252 14.97

3 Casson model 13.46 0.152 – 60.01

4 Bingham model 17.14 0.436 – 100.02

5 Herschel Bulkley model 2.27 13.45 0.278 14.02

*Apparent viscosity Pa s.

Shear rate (s–1)0 20 40 60 80 100 120

Shea

r st

ress

(Pa

)

0

10

20

30

40

50

60

70

Control100 MPa200 MPa300 MPa400 MPa

Shear rate (s–1)0 20 40 60 80 100 120

Shea

r st

ress

(Pa

)

0

10

20

30

40

50

60

Control100 MPa200 MPa300 MPa400 MPa

(a)

(b)

Figure 1 Effect of high-pressure on rheogram of (a) Chousa

mango pulp and (b) Alphanso pulp at 20 �C.



consistency index (K) for Chousa increased signi-

ficantly (P £ 0.05) with pressure treatment while K

was found to decrease for Alphanso pulp

(P > 0.05). However, the trend was not consis-

tent. The effect of the residence time of pressure

treatment on mango pulps is illustrated in Fig. 2.

An increase in K value with time has been found

for Chousa pulp whereas K was much more

constant for canned Alphanso mango pulp. The

difference was possibly due to the fact that the

Chousa pulp was fresh and not heat treated while

the canned Alphonso pulp was obviously heat

treated. The flow behaviour index (n) indicated an

increase in pseudoplasticity for Chousa pulp

(n decreasing from 0.34 to 0.25) while it was

found that pseudoplasticity decreased for Al-

phanso pulp (n increasing from 0.31 to 0.36). The

flow behaviour index reported in the literature for

mango pulp ranged between 0.39 and 0.48 (Bhat-

tacharya, 1999; Pelegrine et al., 2002).

This difference in the magnitudes of the K and

n values of pulps could be caused by the

presence of high molecular weight carbohy-

drates, such as sugar and starch. In the case of

the acidified Alphanso pulp, the maximum con-

version of sugar and starches and inactivation of

enzymes would have occurred during thermal

treatment, and therefore no significant effect was

observed. It is obvious from Table 2a that the

highest magnitude of K and the lowest n for

Chousa pulp was observed at pressure–time

combination of 200 MPa and 30 min. Therefore,

it could be a critical pressure level that contri-

butes to the alteration of the flow characteristics

of pulp.

Thixotropy

Mango pulp treated with HP exhibited thixotropy

(Fig. 3). The area enclosed by the hysteresis loop

signifies the degree of structural breakdown during

steady shearing. The upper curve (0.1–100 s)1) of

the rheogram was found to be higher compared to

the down ward curve (100–0.1 s)1) which indicated

Table 2 Effect of pressure on rheological parameters of (a)

Chousa pulp and (b) Alphanso pulp

Pressure

(MPa)

Duration

(min)

Yield

stress

(Pa)

Consistency

coefficient

(K), Pa sn

Flow

behaviour

index (n) SE

(a)

0.101 – 6.242 8.82 0.338 11.12

100 15 1.151 11.91 0.327 7.83

100 30 2.219 12.09 0.270 9.47

200 15 1.085 14.81 0.260 13.05

200 30 2.657 18.55 0.245 16.28

300 15 1.348 13.26 0.268 11.79

300 30 2.956 15.97 0.267 16.12

400 15 3.779 11.73 0.293 14.31

400 30 2.273 13.45 0.278 14.02

(b)

0.101 – 3.805 11.33 0.309 18.83

100 15 3.642 10.44 0.318 17.38

100 30 4.085 7.613 0.354 16.44

200 15 4.008 8.263 0.345 16.17

200 30 4.707 8.856 0.343 17.26

300 15 5.407 9.163 0.334 16.22

300 30 5.125 8.630 0.345 18.30

400 15 5.260 7.295 0.363 15.77

400 30 6.238 7.681 0.362 17.76

Shear rate (s–1)0 20 40 60 80 100 120

Shea

r st

ress

(Pa

)

0

10

20

30

40

50

60

70

Chousa 15 minChousa 30 minAlphanso 15 minAlphanso 30 min

Figure 2 Effect of residence time of applied of 200 MPa on

rheogram of mango pulps at 20 �C.

Shear rate (s–1)0 20 40 60 80 100 120

Shea

r st

ress

(Pa

)

0

10

20

30

40

50

60

70

Chousa (up)Chousa (down)Alphanso (up)Alphanso (down)

Figure 3 Thixotropy of pressurized pulps at 300 MPa for

30 min at 20 �C.



a thinning of mango pulp with time of shearing.

Similar behaviour was observed by Bhattacharya

(1999) for mango pulp. The rate of thixotropy and

the hysteresis loop area shown by Chousa pulp

treated by at 200 MPa for 30 min was higher than

the control indicating more thixotropy (Fig. 3).

Pressure treatment of canned Alphanso pulp exhib-

ited limited thixotroic behaviour, possibly because

of previous breakdown of texture due to heat

treatment during canning (Table 3). However,

pressure treatment time had no effect on thixo-

tropy.

Effect of high pressure on dynamic rheology of

mango pulp

The dynamic rheological characteristics of mango

pulps are presented in Fig. 4a–d. The dynamic

rheological modulii values (G¢ and G¢¢) of both

mango pulps increased significantly with angular

frequency and G¢ values were much higher than G¢¢at all values of frequency employed. There was no

crossover of G¢ and G¢¢ indicating no gel formation

occurred during HP treatment of mango pulp.

Both G¢ and G¢¢ values increased with frequency

for Chousa pulp as a result of HP treatment at 100

and 200 MPa (both 15 and 30 min) while at, or

above, 300 MPa both parameters decreased. On

the contrary, a steadily decreasing trend of G¢ andG¢¢ was found for Alphanso pulp treated with

pressure. No significant differences (P > 0.05)

were observed between HP treatment times of 15

and 30 min for both pulps.

The experimental data of G¢ and G¢¢ fitted a

polynomial equation (Rheology Advantage, TA

version 2.3) adequately with standard errors <3.

The coefficients to the third order are systematic

with the experiments and therefore rheological

parameters to the third order are presented in

Table 4. Rheological coefficients support the idea

that there was dynamic rheological behaviour of

mango pulp with variation of rheological param-

eters above 200 MPa.

Effect of high pressure on visual colour of mango

pulp

The colours of mango pulps treated with HP are

presented in Table 5 for Chousa and Alphanso,

respectively. The changes in the values of the

three-colour parameters (L, a and b) of Chousa

pulp with pressure treatment were not significant

(P > 0.05). The quality parameter (a/b), C and h

remained almost constant indicating minimal

effect on pigments. The total colour difference

(DE), which takes into account the evolution of

the three colour parameters, decreased with an

increase in pressure intensity with Chousa (fresh)

pulp. Higher pressures decreased the magnitude of

DE while treatment time had no effect. For

Alphanso pulp the changes in colour b values

(represents carotenoids), parameters a/b and C

and h values were not significant. The magnitude

of (DE) for Alphanso pulp increased following a

30-min treatment at ‡300 Mpa, this indicated an

initiation of browning. This could be because of

browning of thermal processed pulp during pres-

surization at higher level. The browning is evident

from the increase of colour �a� value and decrease

of �b� values at ‡300 MPa.

This retention of colour of mango pulp during

HP processing was supported by earlier work of

Fernandez et al. (2001) on tomato puree. They

found no effect of pressurization on pigments

(b-carotene and lycopene) of tomato puree

during HP treatment (Fernandez et al., 2001).

However, contradictory results were reported by

other researchers (Arrayo et al., 1997; Prestamo

& Arroyo (1998). These researchers reported

that browning occurred after HP treatment of

some vegetable products and the products

become unacceptable to the consumers because

Table 3 Effect of high pressure on thixotropy of mango

pulps at 20 �C

Pressure

(MPa)

Duration

(min)

Area under the

curve (1 s)1 Pa)

Thixotropy

(Pa s)1)

Chousa Alphanso Chousa Alphanso

0.101 – 16.23 2.40 284 89.5

100 15 17.20 5.04 323.1 131.0

100 30 17.77 5.65 373.8 132.5

200 15 18.76 3.63 356.5 107.7

200 30 17.63 4.31 332.6 112.6

300 15 17.82 3.12 323.9 119

300 30 19.06 2.62 373.1 108.7

400 15 16.28 2.58 259.8 107.9

400 30 20.88 1.42 336 81.36



of retention of peroxidase and polyphenol

oxidase enzymes.

Effect of high pressure on glass transition of

mango pulp

The glass transition temperature of mango pulp

was determined for both fresh and processed

mango pulps. The Tg of both samples remained

constant ()87.45 and )88.73 �C and )85.34 and

84.74 �C for fresh and processed) during pressure

treatment. It is concluded that HP did not alter

the sugar composition of mango pulp signifi-

cantly.

Conclusion

Rheological properties of HP treated fresh mango

pulp were more complex than those of heat

processed pulp. The effect of pressure level was

Angular frequency (rad s–1) Angular frequency (rad s–1)

Angular frequency (rad s–1) Angular frequency (rad s–1)

100 x 10–3 1 x 100 10 x 100 100 x 100

G/ (

Pa)

G/ (

Pa)

100

1000

Control200 MPa 30 min300 MPa 30 min400 MPa 30 min

0.1 1.0 10.0 100.010

100

1000


0.1 1 10 100

100

1000


0.1 1.0 10.0 100.0

G// (

Pa)

G// (

Pa)

10

100

1000


(a) (b)

(c) (d)

Figure 4 Effect of pressure on (a) storage modulus of Chousa pulp, (b) loss modulus of Chousa pulp, (c) storage modulus of

Alphanso pulp (d) loss modulus of Alphanso pulp.



more significant than that of the treatment time on

the rheology and colour of fresh mango puree.

Moderate pressures (100–200 MPa) increased the

rheological parameters of fresh pulp while a

decreasing trend was found at higher pressure

levels (300–400 MPa). A steady decrease was

noticed with heat treated mango pulp. Colour

was retained in mango pulp treated by HP and this

was found to be the best example of an unchanged

quality attribute during HP processing. More

studies are necessary on the inactivation of

enzymes in the pulp, namely polyphenol oxidase

and peroxidase. A microbiological study would

reveal the safety of the process and the suitability

of the process for the industry. Studies using

scanning electron microscopy could provide data

on the exact textural variation during HP treat-

ment.

Table 4 Dynamic rheological parameters of (a) Chousa mango pulp and (b) Alphanso mango pulp at residence time of 30 min

at 20 �C

Pressure (MPa)

Storage modulus Loss modulus

a0 a1 a2 a3 SE a0 a1 a2 a3 SE

(a)

0.101 397.0 138.8 33.98 )24.03 0.84 96.29 64.98 25.91 2.54 1.81

100 410.5 141.2 29.25 )5.47 1.12 101.2 67.55 17.50 3.76 1.57

200 424 144.5 27.11 )4.47 1.74 105 70.90 12.63 4.67 4.66

300 394.3 129.2 36.44 )9.32 0.98 95.53 67.02 26.61 5.15 2.82

400 358.9 117.3 29.51 )7.57 1.58 84.62 57.02 18.2 8.015 3.46

(b)

0.101 192.7 66.10 17.32 )3.52 0.89 52.23 40.51 22.33 12.44 1.58

100 160.7 52.22 13.90 )11.19 0.60 43.08 34.61 19.06 3.52 2.71

200 181.7 58.84 16.46 )6.98 0.76 50.05 40.04 21.53 )1.13 0.70

300 178.2 56.93 13.16 )7.16 0.84 48.40 39.11 22.66 2.89 1.48

400 156.6 57.78 13.55 )9.88 0.61 46.28 38.49 20.86 0.63 1.47

Table 5 Effect of pressure on tristimulus colour of (a) Chousa pulp and (b) Alphanso pulp

Pressure (MPa) Duration (min) L a b a/b C H DE

(a)

0.101 – 54.23 8.49 33.28 0.255 34.34 75.7

100 15 49.11 7.37 28.95 0.255 29.87 75.70 6.80

100 30 49.69 7.44 27.55 0.270 28.53 74.89 7.39

200 15 51.01 7.76 29.92 0.260 30.92 75.43 4.70

200 30 49.38 8.01 33.10 0.242 34.06 76.38 4.88

300 15 51.62 7.69 32.33 0.238 33.24 76.61 2.89

300 30 51.61 8.22 33.14 0.248 34.15 75.12 2.64

400 15 51.28 8.18 32.75 0.250 33.76 76.70 3.01

400 30 51.33 8.37 32.55 0.257 33.61 75.24 2.99

(b)

0.101 – 51.05 14.32 39.69 0.361 42.19 70.15

100 15 51.19 14.12 36.16 0.390 38.82 68.89 3.58

100 30 51.46 14.20 36.27 0.392 38.95 68.62 3.44

200 15 51.81 13.98 36.00 0.388 38.63 68.78 3.77

200 30 50.60 14.16 36.67 0.386 39.30 69.58 3.06

300 15 51.07 14.35 35.93 0.399 38.69 65.55 3.76

300 30 51.02 13.95 35.13 0.397 37.80 65.94 4.57

400 15 51.51 14.13 34.97 0.404 37.71 66.32 4.75

400 30 51.55 14.28 34.87 0.410 37.68 66.08 4.84



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The effect of high pressure treatment on rheological characteristics and colour of mango pulp

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