Rheological properties of ultraviolet irradiated and thermally pasteurized yankee pineapple juice

Rheological properties of ultraviolet-irradiated and thermally pasteurizedYankee pineapple juice a Department of Process and Food Engineering, Faculty of Engineering, Universiti Putra Ma

Rheological properties of ultraviolet-irradiated and thermally pasteurized

Yankee pineapple juice

a

Department of Process and Food Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

b

Department of Food Technology, Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

c

Department of Chemical and Process Engineering, Faculty of Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

a r t i c l e i n f o

Article history:

Received 21 February 2012

Received in revised form 20 November 2012

Accepted 21 December 2012

Available online 28 December 2012

Keywords:

Pineapple

Pasteurization

Juice

Viscosity

Arrhenius

a b s t r a c t

The rheological behaviour of Yankee pineapple juice was examined for the effect of ultraviolet (UV) irra-diation (53.42 mJ/cm2) and compared with untreated juice and a thermally pasteurized (80 °C for 10 min) juice A rheological test was performed on all types of juice in the temperature range 5 °C to 25 °C using a concentric cylinder rheometer at a shear rate range of 10–290 s1 The comparative analysis found that the best flow curves were described by the Bingham model with an initial shear stress The entangled pulps in the juices prevented free flow at zero shear rate There was no significant variation between the plastic viscosities of the untreated and UV-irradiated juice at all temperatures The activation energy (Ea) of the untreated, UV-irradiated and thermally pasteurized juice was 6.80, 8.19 and 8.50 kJ/mol respectively

Ó 2012 Elsevier Ltd All rights reserved

1 Introduction

The outgrowth of pathogenic microorganisms and bacteria is a

common occurrence in fresh or unpasteurized juice Thermal

pas-teurization is identified as an effective disinfection technology to

Ultraviolet irradiation has an advantage over thermal processing

in terms of the overall food product quality Ultraviolet irradiation

is a non-thermal technology that is used to destroy foodborne

Barbosa-Canovas, 2004) Non-thermal technologies preserve the

‘fresh-like’ quality characteristics and have a minimal effect on

In the processing of fruit juice, many variables exist that can

han-dling and processing, quality control and sensory evaluation of

useful for the prediction of heat and mass coefficients and for the

design or development of heat and mass transfer equipment in

varia-tions result in some operational effects such as concentration by

evaporation and reverse osmosis, pumping, homogenization and

a fruit juice is influenced by factors such as the variety or the maturity of the fruit and the treatment applied to the fruit juice All these factors affect the consumer acceptability of the fruit juice (Juszczak and Fortuna, 2003; Tiziani and Vodovotz, 2005; Aguilo-Aguayo et al., 2009)

Most of the reported studies are concerned with the effect of thermal pasteurization treatment on the rheological behaviour of

2003, 2005; Hernandez et al., 1995), carrot juice (Vandresen

et al., 2009), strawberry juice (Aguilo-Aguayo et al., 2009) and

the rheological behaviour of UV-irradiated juice is limited As far

as the current authors are aware, no published data is currently available concerning the effect of UV irradiation on the rheological behaviour of fruit juice Therefore, this study is aimed at evaluating the rheological behaviour of UV-irradiated and thermally pasteur-ized pineapple juice as a function of temperature and to determine the best rheological model to fit to the juices

2 Materials and methods 2.1 Preparation of pineapple juice Pineapple fruits (Ananas comosus L.) of the Yankee variety at commercial maturity were purchased from a commercial farm in 0260-8774/$ - see front matter Ó 2012 Elsevier Ltd All rights reserved.

⇑Corresponding author Tel.: +60 3 89466366; fax: +60 3 86567123.

E-mail address: rosnahs@eng.upm.edu.my (R Shamsudin).

Journal of Food Engineering

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 / j f o o d e n g

Selangor, Malaysia After washing the fruits, the skins were peeled

off using a meat slicer (300SL, DEUGI, Italy) The flesh of the fruit

was cut into smaller pieces using a food slicer (ECA-201, EMURA,

Japan) Then, the juice was produced using a Supermass Colloider

(ZA10-20J, MASAKO, Japan), an ultra-fine friction grinder and

tered through a bean grinder (MH-280, Taiwan) The juice was

(BS410-1, ALPHA, England) prior to treatment

2.2 Ultraviolet treatment

Filtered pineapple juice was treated using the CiderSure 3500-B

Laboratory Unit (Macedon, New York) This laboratory unit

con-sists of a process tube in which the fluid flows and is fitted with

electronic controls The process tube is made up of two concentric

tubes (outer stainless steel grade 304 and inner quartz tube

stacked vertically) and sensors The source of the UV irradiation

is eight low pressure lamps which emit 90% of UV light at

254 nm wavelength These lamps are enclosed by the quartz tube

Juice was pumped through a 0.762 mm thin film which is the

annular space between the stainless steel tube and quartz tube

Sensors are placed in the bottom and top part of the process tube

and maintain a gap of 0.483 mm between the ends of the rod

sen-sor and the inner quartz tube The sensen-sors provide the information

for the UV dosage calculations The touch screen of the laboratory

unit is used for the adjustment of the process parameters and for

monitoring the status of the operational sensors such as the lamps

and drive

2.3 Ultraviolet processing parameters

The juices were pumped and flowed into the ultraviolet

labora-tory unit at a flow rate of 2.59 L/min which was exposed to the

the total radiant energy passing through a sphere with a very small

following equation

UV dosage ðmJ=cm2Þ ¼ irradiance ðmJ=cm2sÞ

where irradiance is determined by the sensor devices and the

expo-sure time is obtained by dividing the UV expoexpo-sure surface area and

length of processing tube by the flow rate The method of

2.4 Thermal pasteurization treatment

For the pasteurization treatment, the filtered juices were

cov-ered in an electric jacketed kettle (Sul Supplies (M) Sdn Bhd,

Malaysia) and heated to 80 °C and held for 10 min According to

Azam (2008), fruit juices are pasteurized at temperatures of 80–

95 °C for 1–10 min for the purposes of preservation The

tempera-ture of the juice during the heating process was monitored using a

type K-thermocouple (1319A, TES Electrical Electronic Corp.,

Tai-wan) with an accuracy of ±1 °C The pasteurized juices were then

hot filled into sterilized glass bottles and capped with sterilized

caps

2.5 Rheological measurement

A rheometer (Dynamic Controlled Stress 600 Rheometer,

Ther-mo Electron Corporation, Germany) complete with measuring and

evaluation computer software (Haake Rheowin, Thermo Electron

Corporation, Germany) was used to determine the rheological

behaviour of the untreated (fresh), UV-irradiated and thermally

pasteurized pineapple juice Measurement of the rheological prop-erties was carried out using a concentric cylinder system equipped with a Rotor Z40 DIN and Messbecher Z40 Cup According to Shamsudin et al (2009), a shear rate range below 500 s1is mostly used in the juice industry In this study, the sample of untreated, UV-irradiated and thermally pasteurized juices were better

sam-ple juice were tested at temperatures of 5 °C, 10 °C, 15 °C, 20 °C and

25 °C Temperatures below 25 °C were selected considering that

UV irradiation is a non-thermal process whereby the temperature used should not be higher than the ambient temperature Also, these temperatures are extensively used in the food industry for manufacturing, storage, transport, sale and consumption purposes The temperature was regulated by a circulating water bath (DC 30-K20, Thermo Electron Corporation, Germany) with a temperature accuracy of ±0.01 °C Experiments were performed in duplicate and two replications were conducted for each experiment

2.6 Rheological equations Software NLREG (Sherrod., USA) was used for the rheological data analysis The rheological data from the experiments were fit-ted to an existing model such as Newtonian, Bingham and Ost-wald-de-Waele (Power Law) rheological models The above mentioned models are represented by

The Arrhenius equation that is used to describe the effect of temperature on viscosity is as follows:

g¼ Kexp Ea

RT

 

ð5Þ

2.7 Statistical analysis

A one-way analysis of variance (ANOVA) was applied to com-pare the experimental treatments Differences among treatment means were determined by the Tukey test A value of p < 0.05 indi-cated the differences to be significant All statistical analyses were conducted using SPSS Version 13.0 software (SPSS Inc., USA)

3 Results and discussion 3.1 Flow curves

A rheological test of untreated, UV-irradiated and thermally pasteurized pineapple juice was carried out in the temperature range of 5–25 °C to obtain the flow curve (shear stress versus shear

pineap-ple juice at five different temperatures 5 °C, 10 °C, 15 °C, 20 °C and

25 °C As can be observed from the figure, the flow curves of the untreated pineapple juice at the five different temperatures dem-onstrate an initial yield stress, indicating the presence of entangled pulp which prevents the free flow of the juices at zero shear rates Similar flow curves were observed in the UV-irradiated and

ther-mally pasteurized pineapple juice at all temperatures as can be

3.2 Selection of rheological model

Table 1shows the fitted parameters of the Newtonian, Bingham

and Ostwald-de-waale (Power Law) rheological models for the

un-treated, UV-irradiated and thermally pasteurized pineapple juice at

temperature 5 °C, 10 °C, 15 °C, 20 °C and 25 °C The best rheological

model for describing the flow behaviour of juices was selected by

experimen-tal results showed that the flow characteristics of the untreated,

UV-irradiated and thermally pasteurized pineapple juice obtained

the best adjustment of data in the Bingham model with high values

(2008)reported similar work for pineapple juice containing pulp

from variety Josapine Fresh pineapple juices which contain 0%,

10%, 20%, 30% and 40% pulp exhibited a yield stress in the

temper-ature range 5–65 °C and the flow behaviours were best fitted by

the Bingham equation The results showed that the Bingham

plas-tic viscosity of the untreated, UV-irradiated and thermally

pasteur-ized pineapple juice decreased with increased temperature

However, there is no trend for the yield stress value of the

un-treated, UV-irradiated and thermally pasteurized pineapple juice

with temperature and this indicates that the yield stress of these

three types of pineapple juice are not affected by temperature

3.3 Plastic viscosity

Table 2shows the plastic viscosity of the untreated,

UV-irradi-ated and thermally pasteurized pineapple juice at five different

temperatures (5 °C, 10 °C, 15 °C, 20 °C and 25 °C) There was no

sig-nificant variation in the plastic viscosities between the untreated

and UV-irradiated juice at all five different temperatures However, the plastic viscosity of the thermally pasteurized juice was signif-icantly (p < 0.05) higher than the untreated and UV-irradiated juice

(2003), the application of technology to process juice may cause changes in the viscosity Particle size, shape and volume fraction

is subjected to heat treatment, the particle size of the juice be-comes larger and consequently coagulates the colloidal materials (Vandresen et al., 2009; Yeom et al., 2000) These colloidal materi-als contribute to the increasing of viscosity of the juice In addition, the ‘swelling’ of the particles and the penetration of water between the cellulose chains during heating induces the high viscosity of

the juice is due to the reduction of PME (pectin methylesterase) and PG (polygalacturonase) activity or the coagulation of protein

a polysaccharide which contributes a viscous characteristic to the

structure is greatly ruptured during the treatment of juices and the more soluble pectin leaks out from the cell walls A high viscos-ity in the product might also be attributed to a highly concentrated

carrot juice increased significantly after pasteurization treatment Moreover, a higher viscosity was observed in heated watermelon

Aguilo-Aguayo et al., 2010)

On the other hand, no significant differences in plastic viscosi-ties were found among the thermally pasteurized, UV-irradiated

Ta-ble 2) At the highest temperature, the thermal energy caused a rearrangement of the particles in parallel directions and lead to the breaking up of these particles into smaller particles These par-ticles can flow more easily and result in a reduction of the

plastic viscosity of the thermally pasteurized juice was not very different from the untreated and UV-irradiated juice at tempera-tures greater than 15 °C

3.4 Effect of temperature on the plastic viscosity The plastic viscosity of the untreated, UV-irradiated and ther-mally pasteurized pineapple juice decreased with increasing

(2009)andConstenla et al (1989), the viscosity of a solution is af-fected by the intermolecular forces and water–solute interactions

0

0.5

1

1.5

2

2.5

3

3.5

Shear rate (s-1)

Fig 1 Flow curves of untreated pineapple juice at different temperature.

0

0.5

1

1.5

2

2.5

3

3.5

Shear rate (s-1)

Fig 2 Flow curves of ultraviolet irradiated pineapple juice at different

0 0.5 1 1.5 2 2.5 3 3.5

Shear rate (s -1 )

5 10 15 20 25

Fig 3 Flow curves of thermally pasteurized pineapple juice at different temperature.

that limit the movement at the molecular level Changes in

tem-perature and concentration may influence these forces When the

juice undergoes a heating process, the thermal energy of the

mol-ecules increases and the intermolecular distances also increase due

to thermal expansion, which therefore leads to a reduction in

pas-teurized carrot juice in which the viscosity decreased as the

temperature increased from 8 °C to 25 °C The effect of

tempera-ture on the rheological behaviour of fruit juice can be described

1982; Saravocos, 1970):

Fig 4 shows the applicability of the Arrhenius model to the plastic viscosity of untreated, UV-irradiated and thermally pasteur-ized pineapple juices The parameters for the Arrhenius model,

model for the untreated, UV-irradiated and thermally pasteurized pineapple juice The experimental data was satisfactorily described

the range of 0.9140–0.9775 The activation energy is the threshold energy that must be overcome before the elementary flow process

sig-nificant difference in the activation energy among the untreated (6.80 ± 1.35 kJ/mol), UV-irradiated (8.19 ± 1.07 kJ/mol) and ther-mally pasteurized juice (8.50 ± 2.14 kJ/mol) This result agrees with

acti-vation energy between the untreated and pasteurized carrot juice was not significantly different

However, the thermally pasteurized juice indicated a non-sig-nificant increase (p > 0.05) in the activation energy compared to both the untreated and UV-irradiated juice A higher value of acti-vation energy indicates the higher temperature effect on the

with temperature occurs in a system when the activation energy

the activation energy in juice concentrate is due to the high

the thermally pasteurized pineapple juice had the higher soluble

(13.6 °Brix) and untreated juice (13.4 °Brix) Therefore, the ther-mally treated pasteurized pineapple juice demonstrated a higher activation energy than the untreated and UV-irradiated juice

en-Table 1

Experimental data fitted to parameters of rheological models (Newtonian, Bingham and Power Law).

Untreated

Ultraviolet

Thermal

Group means with the same letters in a column are significantly different at 5% level of significant by Tukey test.

Table 2

Plastic viscosity of untreated, ultraviolet irradiated and thermal pasteurized

pineap-ple juice at different temperature.

Temperature (°C) Plastic viscosity (Pa s)

Untreated Ultraviolet Thermal

5 0.0088 ± 0.0007 a

0.0089 ± 0.0004 a

0.0100 ± 0.0004 b

10 0.0082 ± 0.0008 a

0.0083 ± 0.0010 a

0.0094 ± 0.0003 b

15 0.0081 ± 0.0008 a 0.0080 ± 0.0007 a 0.0089 ± 0.0002 a

20 0.0076 ± 0.0005 a 0.0076 ± 0.0008 a 0.0084 ± 0.0001 a

25 0.0072 ± 0.0004 a

0.0069 ± 0.0006 a

0.0078 ± 0.0001 a Values follow by the same letter within the same row are not significantly different

from each other (p > 0.05).

-5.1

-5

-4.9

-4.8

-4.7

-4.6

-4.5

7 0 0 5

0 0 3

0

0

1/T (1/K) Untreated Ultraviolet Thermal

Fig 4 Applicability of the Arrhenius model to the plastic viscosity of untreated,

Table 3 Experimental data fitted to parameters of Arrhenius model.

Treatment K  (Pa s) E a (kJ/mol) R 2 Untreated 5.03  10 4 ± 2.18  10 4a 6.80 ± 1.35 a 0.9140 Ultraviolet 3.13  10 4 ± 2.25  10 4a 8.19 ± 1.07 a 0.9317 Thermal 3.01  10 4 ± 1.08  10 4a 8.50 ± 2.14 a

0.9775 Values follow by the same letter within the same column are not significantly different from each other (p > 0.05).

ergy in Newtonian fluid foods increases from 14.4 kJ/mol for water

to more than 60 kJ/mol for concentrated clear juices and sugar

en-ergy of blueberry and raspberry juice increased as the solids

con-tent increased from 10 to 65 °Brix

non-significant (p > 0.05) lower value than the untreated and

UV-irradiated juice In this study, the thermally pasteurized juice

which had a higher amount of soluble solids, exhibited a higher

untreated and UV-irradiated juice As a result, the activation

re-ported that the activation energy of fresh pineapple juice increased

and value of the material constant decreased with an increase in

the soluble solids content (4–14 °Brix) Similar findings were also

observed in clarified concentrated strawberry juice (50–67.1 °Brix)

(Juszczak and Fortuna, 2003) and concentrated peach juice (40–

in-crease in the soluble solids content

4 Conclusion

Untreated, UV-irradiated and thermally pasteurized pineapple

juice both behaved as non-Newtonian fluids with the existence

of yield stress at temperatures 5 °C, 10 °C, 15 °C, 20 °C and 25 °C

The flow characteristics of all types of juice were best described

by the Bingham model with a high correlation coefficient There

was no significant difference in the plastic viscosity between the

UV-irradiated and untreated juice at temperatures of 5 °C, 10 °C,

15 °C, 20 °C and 25 °C However, a significant increase of plastic

viscosity was observed in the thermally pasteurized juice at

tem-peratures of 5 °C and 10 °C As a result, it can be observed that

the ultraviolet irradiation did not have any significant effect on

the rheological behaviour of the pineapple juice and it preserved

similar quality attributes as the untreated juice The Arrhenius

equation was successfully applied to describe the effect of

temper-ature on the plastic viscosity of the juices The plastic viscosity of

the untreated, UV-irradiated and thermally pasteurized juice

de-creased with increasing temperature from 5 °C to 25 °C

Acknowledgements

This project was funded by the Fundamental Research Grant

Scheme (03-04-10-802FR) The authors wish to record their sincere

gratitude to the Federal Agriculture Marketing Authority (FAMA)

for providing the fruit samples used in this study

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