Journal of Food Engineering 116 (2013) 548–553 Contents lists available at SciVerse ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng Rheological properties of ultraviolet-irradiated and thermally pasteurized Yankee pineapple juice Rosnah Shamsudin a,⇑, Chia Su Ling a, Noranizan Mohd Adzahan b, Wan Ramli Wan Daud c a Department of Process and Food Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia 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 b 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) irradiation (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 °C to 25 °C using a concentric cylinder rheometer at a shear rate range of 10–290 sÀ1 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 Introduction The outgrowth of pathogenic microorganisms and bacteria is a common occurrence in fresh or unpasteurized juice Thermal pasteurization is identified as an effective disinfection technology to prolong the shelf life of juice products (Aguilo-Aguayo et al., 2009) However, the thermal process may impair the nutritional and sensory quality attributes of the juice (Caminiti et al., 2011) 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 pathogens or microorganisms in foods (Guerrero-Beltran and Barbosa-Canovas, 2004) Non-thermal technologies preserve the ‘fresh-like’ quality characteristics and have a minimal effect on the nutritional and organoleptic properties (Adekunte et al., 2010) In the processing of fruit juice, many variables exist that can lead to changes in the final product quality (Juszczak and Fortuna, 2003) Rheology studies of food play an important role in the handling and processing, quality control and sensory evaluation of various foods (Rao, 1999) Knowledge of the rheology properties is useful for the prediction of heat and mass coefficients and for the design or development of heat and mass transfer equipment in the fruit juice industry (Abdulagatov et al., 2008) Viscosity variations result in some operational effects such as concentration by ⇑ Corresponding author Tel.: +60 89466366; fax: +60 86567123 E-mail address: rosnahs@eng.upm.edu.my (R Shamsudin) 0260-8774/$ - see front matter Ó 2012 Elsevier Ltd All rights reserved http://dx.doi.org/10.1016/j.jfoodeng.2012.12.031 evaporation and reverse osmosis, pumping, homogenization and blending (Abdulagatov et al., 2008) Furthermore, the viscosity of 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; AguiloAguayo et al., 2009) Most of the reported studies are concerned with the effect of thermal pasteurization treatment on the rheological behaviour of fruit juice These studies include orange juice (Polydera et al., 2003, 2005; Hernandez et al., 1995), carrot juice (Vandresen et al., 2009), strawberry juice (Aguilo-Aguayo et al., 2009) and watermelon juice (Aguilo-Aguayo et al., 2010) Information about 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 pasteurized pineapple juice as a function of temperature and to determine the best rheological model to fit to the juices 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 R Shamsudin et al / Journal of Food Engineering 116 (2013) 548–553 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 filtered through a bean grinder (MH-280, Taiwan) The juice was filtered again using a 500l aperture stainless steel sieve screen (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 consists 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 sensor and the inner quartz tube The sensors 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 The juices were pumped and flowed into the ultraviolet laboratory unit at a flow rate of 2.59 L/min which was exposed to the ultraviolet dosage at 53.42 mJ/cm The UV dosage is defined as the total radiant energy passing through a sphere with a very small cross-sectional area (Sastry et al., 2000) and is calculated by the following equation UV dosage ðmJ=cm2 Þ ¼ irradiance ðmJ=cm2 sÞ Â exposure time ðsÞ pasteurized pineapple juice Measurement of the rheological properties 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 sÀ1 is mostly used in the juice industry In this study, the sample of untreated, UV-irradiated and thermally pasteurized juices were better described at a shear rate varying from 50 to 290 sÀ1 All types of sample juice were tested at temperatures of °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 30K20, 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 replication (Halim et al., 2012) 2.6 Rheological equations Software NLREG (Sherrod., USA) was used for the rheological data analysis The rheological data from the experiments were fitted to an existing model such as Newtonian, Bingham and Ostwald-de-Waele (Power Law) rheological models The above mentioned models are represented by Newtonian : r ¼ gc_ Ostwald-de-Waele : 2.3 Ultraviolet processing parameters ð1Þ 549 Bingham : ð2Þ r ¼ kc_ n r À r ¼ g0 c_ ð3Þ ð4Þ where r is the shear stress (Pa), c_ is the shear rate (sÀ1), g is the viscosity (Pa s), g0 is the plastic viscosity, r is the yield stress (Pa), k is the consistency index (Pa½ sn) and n is the flow behaviour index The Arrhenius equation that is used to describe the effect of temperature on viscosity is as follows: g ¼ K  exp  Ea RT  ð5Þ where irradiance is determined by the sensor devices and the exposure time is obtained by dividing the UV exposure surface area and length of processing tube by the flow rate The method of calculating the UV dosage has been reported in detail by Canitez (2002) where K is a constant, Ea is the activation energy (J molÀ1), R is the gas constant (J molÀ1 KÀ1) and T is the absolute temperature (K) 2.4 Thermal pasteurization treatment A one-way analysis of variance (ANOVA) was applied to compare the experimental treatments Differences among treatment means were determined by the Tukey test A value of p < 0.05 indicated the differences to be significant All statistical analyses were conducted using SPSS Version 13.0 software (SPSS Inc., USA) For the pasteurization treatment, the filtered juices were covered in an electric jacketed kettle (Sul Supplies (M) Sdn Bhd, Malaysia) and heated to 80 °C and held for 10 According to Azam (2008), fruit juices are pasteurized at temperatures of 80– 95 °C for 1–10 for the purposes of preservation The temperature of the juice during the heating process was monitored using a type K-thermocouple (1319A, TES Electrical Electronic Corp., Taiwan) 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, Thermo 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 2.7 Statistical analysis 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 rate) data Fig represents the flow curve of the untreated pineapple juice at five different temperatures °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 demonstrate 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- R Shamsudin et al / Journal of Food Engineering 116 (2013) 548–553 3.5 3.5 3 2.5 2.5 Shear stress (Pa) Shear stress (Pa) 550 1.5 0.5 10 15 20 1.5 0.5 25 10 15 20 25 0 50 100 150 200 Shear rate (s -1) 250 300 350 Fig Flow curves of untreated pineapple juice at different temperature mally pasteurized pineapple juice at all temperatures as can be seen in Figs and 3.2 Selection of rheological model Table shows the fitted parameters of the Newtonian, Bingham and Ostwald-de-waale (Power Law) rheological models for the untreated, UV-irradiated and thermally pasteurized pineapple juice at temperature °C, 10 °C, 15 °C, 20 °C and 25 °C The best rheological model for describing the flow behaviour of juices was selected by comparing the value of correlation coefficient, R2 The experimental 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 of R2 > 95% which were in the range of 0.9972–0.9998 Shamsudin (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 temperature range 5–65 °C and the flow behaviours were best fitted by the Bingham equation The results showed that the Bingham plastic viscosity of the untreated, UV-irradiated and thermally pasteurized pineapple juice decreased with increased temperature However, there is no trend for the yield stress value of the untreated, 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 shows the plastic viscosity of the untreated, UV-irradiated and thermally pasteurized pineapple juice at five different temperatures (5 °C, 10 °C, 15 °C, 20 °C and 25 °C) There was no significant variation in the plastic viscosities between the untreated 3.5 Shear stress (Pa) 2.5 1.5 50 100 150 200 250 300 350 Shear rate (s -1) Fig Flow curves of thermally pasteurized pineapple juice at different temperature and UV-irradiated juice at all five different temperatures However, the plastic viscosity of the thermally pasteurized juice was significantly (p < 0.05) higher than the untreated and UV-irradiated juice at temperatures °C and 10 °C According to Juszczak and Fortuna (2003), the application of technology to process juice may cause changes in the viscosity Particle size, shape and volume fraction influence the viscosity of the juice (Lozano, 2006) When the juice is subjected to heat treatment, the particle size of the juice becomes larger and consequently coagulates the colloidal materials (Vandresen et al., 2009; Yeom et al., 2000) These colloidal materials 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 pasteurized juice (Vandresen et al., 2009; Cheftel and Cheftel, 1992) Protein coagulation occurs in the pasteurized pineapple juice (Grassin and Coutel, 2010) The increase in the viscosity of the juice is due to the reduction of PME (pectin methylesterase) and PG (polygalacturonase) activity or the coagulation of protein tissue (Aguilo-Aguayo et al., 2009; Porreta et al., 1995) Pectin is a polysaccharide which contributes a viscous characteristic to the juice (Yen and Lin, 1998) According to Hayes et al (1998), cell structure is greatly ruptured during the treatment of juices and the more soluble pectin leaks out from the cell walls A high viscosity in the product might also be attributed to a highly concentrated pectin colloidal solution (Aguilo-Aguayo et al., 2010; Si-Ying et al., 1986) Similarly, Vandresen et al (2009) reported the viscosity of carrot juice increased significantly after pasteurization treatment Moreover, a higher viscosity was observed in heated watermelon juice compared to the unprocessed watermelon juice (AguiloAguayo et al., 2010) On the other hand, no significant differences in plastic viscosities were found among the thermally pasteurized, UV-irradiated and untreated juice at temperatures 15 °C, 20 °C and 25 °C (Table 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 particles can flow more easily and result in a reduction of the particleparticle interaction force (Vandresen et al., 2009) Therefore, the plastic viscosity of the thermally pasteurized juice was not very different from the untreated and UV-irradiated juice at temperatures greater than 15 °C 3.4 Effect of temperature on the plastic viscosity 0.5 10 15 20 25 0 50 100 150 200 Shear rate (s -1) 250 300 350 Fig Flow curves of ultraviolet irradiated pineapple juice at different temperature The plastic viscosity of the untreated, UV-irradiated and thermally pasteurized pineapple juice decreased with increasing temperature as can be seen in Table According to Kumoro et al (2009) and Constenla et al (1989), the viscosity of a solution is affected by the intermolecular forces and water–solute interactions 551 R Shamsudin et al / Journal of Food Engineering 116 (2013) 548–553 Table Experimental data fitted to parameters of rheological models (Newtonian, Bingham and Power Law) Temperature (°C) Newtonian Bingham Power Law R n k R2 0.0093 0.0090 0.0089 0.0079 0.0077 0.9998 0.9993 0.9983 0.9972 0.9979 0.9886 0.9812 0.9918 0.9477 0.9356 0.0099 0.0101 0.0095 0.0110 0.0115 0.9987 0.9981 0.9981 0.9959 0.9964 0.2173a 0.0569a 0.0560a 0.0421a 0.0963a 0.0094 0.0093 0.0087 0.0083 0.0075 0.9997 0.9995 0.9981 0.9982 0.9989 0.8659 0.9634 0.9678 0.9779 0.9291 0.0215 0.0117 0.0106 0.0096 0.0117 0.9989 0.9993 0.9977 0.9978 0.9980 0.1584a 0.0777b 0.1397c 0.0500d 0.0917e 0.0096 0.0091 0.0087 0.0085 0.0077 0.9998 0.9997 0.9995 0.9980 0.9990 0.9049 0.9502 0.9060 0.9729 0.9332 0.0172 0.0124 0.01556 0.0101 0.0117 0.9990 0.9989 0.9988 0.9975 0.9982 g R r g Untreated 10 15 20 25 0.0094 0.0092 0.0091 0.0083 0.0082 0.9990 0.9989 0.9981 0.9938 0.9932 0.0184a 0.0339a 0.0252a 0.0847a 0.0966a Ultraviolet 10 15 20 25 0.0105 0.0096 0.0090 0.0085 0.0080 0.9837 0.9984 0.9969 0.9974 0.9941 Thermal 10 15 20 25 0.0103 0.0095 0.0094 0.0087 0.0082 0.9918 0.9976 0.9924 0.9970 0.9949 Group means with the same letters in a column are significantly different at 5% level of significant by Tukey test Table Plastic viscosity of untreated, ultraviolet irradiated and thermal pasteurized pineapple juice at different temperature Temperature (°C) 10 15 20 25 Plastic viscosity (Pa s) Untreated Ultraviolet Thermal 0.0088 ± 0.0007a 0.0082 ± 0.0008a 0.0081 ± 0.0008a 0.0076 ± 0.0005a 0.0072 ± 0.0004a 0.0089 ± 0.0004a 0.0083 ± 0.0010a 0.0080 ± 0.0007a 0.0076 ± 0.0008a 0.0069 ± 0.0006a 0.0100 ± 0.0004b 0.0094 ± 0.0003b 0.0089 ± 0.0002a 0.0084 ± 0.0001a 0.0078 ± 0.0001a Values follow by the same letter within the same row are not significantly different from each other (p > 0.05) that limit the movement at the molecular level Changes in temperature and concentration may influence these forces When the juice undergoes a heating process, the thermal energy of the molecules increases and the intermolecular distances also increase due to thermal expansion, which therefore leads to a reduction in viscosity Vandresen et al (2009) reported a similar finding for pasteurized carrot juice in which the viscosity decreased as the temperature increased from °C to 25 °C The effect of temperature on the rheological behaviour of fruit juice can be described by the Arrhenius relationship (Rao et al., 1984; Vitali and Rao, 1982; Saravocos, 1970): In (Plastic viscosity) (Pas) -4.5 -4.6 -4.7 Fig shows the applicability of the Arrhenius model to the plastic viscosity of untreated, UV-irradiated and thermally pasteurized pineapple juices The parameters for the Arrhenius model, namely K and Ea were obtained from the intercept and slope of the plot (Fig 4) Table shows the parameters of the Arrhenius model for the untreated, UV-irradiated and thermally pasteurized pineapple juice The experimental data was satisfactorily described by the Arrhenius equation with the correlation coefficient (R2) in the range of 0.9140–0.9775 The activation energy is the threshold energy that must be overcome before the elementary flow process can occur (Rao, 1999) As can be seen in Table 3, there was no significant difference in the activation energy among the untreated (6.80 ± 1.35 kJ/mol), UV-irradiated (8.19 ± 1.07 kJ/mol) and thermally pasteurized juice (8.50 ± 2.14 kJ/mol) This result agrees with the findings reported by Vandresen et al (2009), in which the activation energy between the untreated and pasteurized carrot juice was not significantly different However, the thermally pasteurized juice indicated a non-significant increase (p > 0.05) in the activation energy compared to both the untreated and UV-irradiated juice A higher value of activation energy indicates the higher temperature effect on the viscosity (Da Silva et al., 2005) A more rapid change in viscosity with temperature occurs in a system when the activation energy is high (Haminuik et al., 2006; Steffe, 1996) The high value of the activation energy in juice concentrate is due to the high content of soluble solids (Ahmed et al., 2007) In the present study, the thermally pasteurized pineapple juice had the higher soluble solids content (14.4 °Brix) compared to the UV-irradiated (13.6 °Brix) and untreated juice (13.4 °Brix) Therefore, the thermally treated pasteurized pineapple juice demonstrated a higher activation energy than the untreated and UV-irradiated juice According to Krokida et al (2001), the value of the activation en- -4.8 Table Experimental data fitted to parameters of Arrhenius model -4.9 -5 -5.1 0.0033 Untreated 0.0035 1/T (1/K) Ultraviolet Thermal 0.0037 Fig Applicability of the Arrhenius model to the plastic viscosity of untreated, ultraviolet irradiated and thermally pasteurized pineapple juice Treatment K (Pa s) Ea (kJ/mol) R2 Untreated Ultraviolet Thermal 5.03 Â 10À4 ± 2.18 Â 10À4a 3.13 Â 10À4 ± 2.25 Â 10À4a 3.01 Â 10À4 ± 1.08 Â 10À4a 6.80 ± 1.35a 8.19 ± 1.07a 8.50 ± 2.14a 0.9140 0.9317 0.9775 Values follow by the same letter within the same column are not significantly different from each other (p > 0.05) 552 R Shamsudin et al / Journal of Food Engineering 116 (2013) 548–553 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 solution Nindo et al (2005) also reported that the activation energy of blueberry and raspberry juice increased as the solids content increased from 10 to 65 °Brix The values of constant K were found to be 5.03 Â 10À4 ± 2.18 Â 10À4 Pa s for the untreated juice, 3.13 Â 10À4 ± 2.25 Â 10À4 Pa s for the UV-irradiated juice and a figure of 3.01 Â 10À4 ± 1.08 Â 10À4 Pa s was recorded for the thermally pasteurized juice as shown in Table The thermally pasteurized juice exhibited a non-significant (p > 0.05) lower value than the untreated and UVirradiated juice In this study, the thermally pasteurized juice which had a higher amount of soluble solids, exhibited a higher activation energy and a lower constant K value compared to the untreated and UV-irradiated juice As a result, the activation energy of the juices increased and the constant, K decreased as the soluble solids of the juice increased Shamsudin et al (2009) reported 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– 69 °Brix) (Ibarz, 1992), in which the activation energies of the flow increased and the values of the constant K decreased with an increase in the soluble solids content Conclusion Untreated, UV-irradiated and thermally pasteurized pineapple juice both behaved as non-Newtonian fluids with the existence of yield stress at temperatures °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 °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 temperatures of °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 temperature on the plastic viscosity of the juices The plastic viscosity of the untreated, UV-irradiated and thermally pasteurized juice decreased with increasing temperature from °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 References Abdulagatov, A.I., Magerramov, M.A., Abdulagatov, I.M., Azizov, N.D., 2008 Effect of temperature, pressure and concentration on the viscosity of fruit juice: experimental 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plastic viscosity of the thermally pasteurized juice. .. Fig Flow curves of ultraviolet irradiated pineapple juice at different temperature The plastic viscosity of the untreated, UV -irradiated and thermally pasteurized pineapple juice decreased with... the untreated, 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