Influence of Temperature and Solid Concentration on the Physical Properties of Noni (Morinda citrifolia L.) Juice

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1 Food Bioprocess Technol (2011) 4: DOI /s ORIGINAL PAPER Influence of Temperature and Solid Concentration on the Physical Properties of Noni (Morinda citrifolia L.) Juice Andri Cahyo Kumoro & Diah S. Retnowati & Catarina S. Budiyati Received: 12 April 2009 / Accepted: 28 August 2009 / Published online: 19 September 2009 # Springer Science + Business Media, LLC 2009 Abstract The effect of temperature on the physical properties of fresh noni (Morinda citrifolia L.) juice with three different solid concentrations (5, 10, and 15 Brix) was investigated. The flow behaviour index (n) and thermal conductivity (k) were found to increase with the increase in temperature. On the other hand, the juice density (ρ) and consistency coefficient (K) were found to decrease with increasing temperature. The increase in solid concentration leads to increase juice density and consistency coefficient, but reduce flow behaviour index and thermal conductivity. The experimental data were then correlated with temperature and solid concentration using nonlinear regression equations or empirical models. It was found that the physical properties calculated using proposed equations agree well with the experimental data with coefficient of determinations (R 2 ) ranged from to Keywords Noni. Consistency coefficients. Flow behaviour index. Density. Thermal conductivity Nomenclatures a 1,a 2,a 3 Constants in Eq. 7 b 1,b 2,b 3 Constants in Eq. 8 C Solid concentration Brix c 1,c 2,c 3 Constants in Eq. 9 d 1,d 2,d 3 Constants in Eq. 10 k Thermal conductivity of the sample, (W. m 1. C 1 ) K Consistency coefficient, (Pa s n ) A. C. Kumoro (*) : D. S. Retnowati : C. S. Budiyati Department of Chemical Engineering, Faculty of Engineering, Diponegoro University, Prof. H. Sudharto, SH Road, Tembalang Campus, Semarang, Indonesia c.k.andrew@undip.ac.id L Length of the copper cylinder used in Eq. 6, (m) n Flow behaviour index, (-) q Heat flux in the thermal resistance, (W) r Radius, (m) R 1,R 2 External and internal radius of the internal and external cylinder, (m) S Surface area of a cylinder of radius r, (m 2 ) T Temperature, ( C) T 1 Steady state temperature in the internal cylinder, ( C) T 2 Steady state temperature in the immersing cell thermostatic bath, ( C) Greek γ Shear rate, (s 1 ) η Viscosity, (Pa.s) ρ Density, (kg.m 3 ) Introduction Noni is the Hawaiian name for the fruit of Morinda citrifolia L. (Rubiaceae). It is well known as mengkudu in Indonesia, Malaysia, and Singapore (Wang et al. 2002). Noni is native from Southeast Asia to Australia and is cultivated in Polynesia, India, the Caribbean, and Central and northern South America (Dixon et al. 1999; Ross 2001).In traditional pharmacopoeia, the fruit is claimed to prevent and cures several diseases. It is primarily used to stimulate the immune system and thus, to fight bacterial, viral, parasitic, and fungal infections; it is also used to prevent the formation and proliferation of tumours, including malignant ones (Dixon et al. 1999; Earle 2001). Noni juice is also claimed to relieve inflammation. Most noni is consumed as juice, although leaves, flowers, bark, and roots

2 Food Bioprocess Technol (2011) 4: can also be used (Dixon et al. 1999; Earle 2001; McClatchey 2002).Two clinical studies reported a relief of arthritis and diabetes associated with noni consumption (Elkins 1998): the observed beneficial effects may result from certain compounds such as scopoletin, nitric oxide, alkaloids, and sterols and also to the antioxidant potential of noni. As a result of this reputation, consumption of this fruit is currently high, not only in the producing countries, but also in the United States, Japan, and Europe. In response to this demand, some countries such as Costa Rica and Cambodia have increased the fields being cultivated in noni. In these countries, the fruit is often commercialised fresh or as juice in both formal and informal markets, but it is also found as pasteurised juice, either pure or mixed with other juices (usually grape or blackberry). Commercial interest in noni has tremendously increased in recent years, as provided by the number of patents registered. In the United States alone, 19 patents have been registered by the US Patent and Trademark Office since 1976 (USPTO 2005). Noni juice has been recently accepted in the European Union as a novel food, and the commercial noni juices are marketed with total soluble solid ranged from 9 to Brix and ph ranged between 3.4 and 3.6 (European Commission, Scientific Committee for Food 2002). The effect of temperature on flow behaviour must be known in the design of foodprocessing equipment such as evaporators, pasteuriser, pumps, filters, and mixers (Vitali and Rao 1982; Bayindirli 1993). In addition, density and viscosity are quality indices (Alvarado and Romero 1989). Specific pasteurisation conditions are required to produce high quality juice in terms of nutrients content and taste and also to make sure it is safe for consumption. A correct design of pasteurisation unit and conditions of pasteurisation process of fruit juice require the mathematical models which represent operating conditions and physical properties such as consistency coefficient or viscosity, flow behaviour index, density, and thermal conductivity (Constenla et al. 1989). Fruit juices are commonly treated as sugar-containing solutions. The official table of density values for sucrose at 20 C (Plato 1900) is still commonly in use in calculation of density for mechanisation of fruit juice industrial applications (Nagy et al. 1993). However, for more exact calculation, it is advantageous to use specific equations. For juice of common apple (Malus domestica), Constenla et al. (1989) proposed equations that related the density with soluble solids concentration ( Brix) and temperature. Alvarado and Romero (1989) proposed an expression of density as a function of concentration and temperature for fruit juices including apple. Although the physical properties of many liquid foods have been reported (Bayindirli 1993), no report is available in the literature for noni juice. The objectives of the present study are to investigate the effect of temperature (30 70 C) on physical properties of three different concentrations (5, 10, and 15 Brix) of noni juice and to propose empirical mathematical models that can be used to describe the relationship between the temperature, solid concentration, and physical properties of the juice. Materials and Methods Juice Preparation The ripened noni fruits were first washed using tap water. The fruits were then cut into smaller pieces and juiced using laboratory scale juicer/juice extractor (Green Power Co., Model GP-E1503 Gold, Anaheim, CA, USA) to obtain seedless noni juice. The extracted juice was filtered twice to remove the remaining pulp and other impurities. Concentrated juices with various soluble solid contents (5, 10, and 15 Brix) were obtained from the original concentrate using a rotary glass vacuum evaporator (BÜCHI Labortechnik AG, Model R-205, Postfach, Switzerland) at temperature below 60 C. The evaporation chamber was rotated at a constant rotational speed in water bath at 40 C. Soluble solid concentrations were determined in a handheld refractometer (NSG Precision Cells, Model Atago Uricon-N, Farmingdale, NY, USA) at 20 C and expressed as Brix. Consistency Coefficient and Flow Behaviour Index A programmable Brookfield rheometer (Brookfield Engineering Laboratories, Vertriebs GmbH, Model DV-111, Lorch, Germany) was used to determine the viscosity and shear rate of juice. An 8-ml sample was put in the concentric cylinder of the rheometer and heated in water bath (MK70, MLW, Dresden, Germany) at the required temperature (30, 40, 50, 60, and 70 C). From the apparent viscosities measured at different shear rates ranged from 50 to 1,000 s 1, the power law (Eq. 1) parameters were determined (Hasaan and Hobani 1998). h ¼ Kg ðn 1Þ ð1þ Density The relative density was determined in capillary tube pycnometer of 10 ml capacity; the water and juice weight were recorded in analytical balance with g precision (Mettler-Toledo GmbH, Model AL54, Greifensee, Switzerland) after stabilisation in a thermostatic bath (0.1 C). The pycnometer had previously been calibrated with distilled water in a heating process, where the sample pycnometer was weighed at 10 C intervals from 30 to 70 C. The temperature was controlled by a thermostatic water bath

3 1484 Food Bioprocess Technol (2011) 4: (MK70, MLW, Dresden, Germany). The experiments were carried out at temperatures in the range from 30 to 70 C at intervals of 10 C. The densities for noni juices were determined for the concentrations of 5 and 15 Brix. All of these determinations were carried out in triplicate. Density was determined using a specific gravity bottle as shown in Eq. 2 (Earle 1985): density ¼ specific gravity of noni juice density of water at the same temperature Thermal Conductivity ð2þ Thermal conductivity at various temperatures and water contents were measured using the method described by Bellet et al. (1975) based on a cylindrical cell, where the liquid whose properties are determined fills the annular space between two concentric cylinders. The physical characteristic is specified in Fig. 1, which presents: two coaxial copper cylinders (a and b), 180 mm in length, separated by a 2-mm annular space, which was filled with the sample; 50 mm thick covers (c) made of a low thermal conductivity material (0.225 W.m 1 C 1 ) to prevent axial heat transfer; a heater made with a constantan wire (resistance 15 W), electrically insulated by a varnish and coiled around a copper stick; two thermocouples type T to measure the temperature differences between the two cylinders, located at half the length of the cell, with wires placed inside 0.5-mm gaps, parallel to the cell axis. The external diameters of the outer and inner copper cylinders were 34 and 20 mm, respectively, while the internal diameters were 24 and 10 mm for the outer and inner cylinders, respectively. To keep the external temperature constant, the cell was immersed in a thermostatic bath (MK70, MLW, Dresden, Germany) containing ethyl alcohol. The power input to the heater resistance was from a laboratory DC power supply (Emerson Network Power, Model LPS 200-M, Bagumbayan, Quezon City, Philippines), which adjusted the current with a stability of 0.05%. An HP data logger, model B, an HP-IB interface, and an HP PC running a data acquisition program written in IBASIC monitored the temperatures with an accuracy of 0.6 C. In order to measure the temperature, one and three copper constantan thermocouples were embedded in the surfaces of the inner and outer cylinders, respectively. The cell was calibrated with distilled water. In the steady state, conduction inside the cell was described by the Fourier equation in cylindrical coordinates, with boundary conditions corresponding to heat transfer between two concentric cylindrical surfaces kept at constant temperatures, as given by Eqs. 3 ð3þ Tr¼ ð R 1 Þ ¼ T 1 ð4þ Tr¼ ð R 2 Þ ¼ T 2 ð5þ Equation 3 was integrated in the form: k ¼ q log ð R 2=R 1 Þ ð6þ 2pLðT 1 T 2 Þ Statistical Analysis Analysis of variance of experimental data was carried out using SPSS version 11.5 (SPSS 2000), and where appropriate, results were expressed as mean±standard error of the mean. Empirical regression was performed to adjust the models to the data, and the suitability of the fitted models was evaluated by the coefficient of determination (R 2 ), the level of significance (p), and residual analysis. Effect of solid concentration and temperature on the coefficient of consistency, flow behaviour index, thermal conductivity, and density were considered significant at p All of the samples were made in three repetitions, and the experiments were accomplished in triplicate. Power supply c Sample a b Results and Discussions Effect of Temperature and Total Soluble Solids on Consistency Coefficient and Flow Behaviour Index Thermocouple (e) Heater (d) Thermocouple (e) Fig. 1 Cross-sectional view of thermal conductivity measurement apparatus Figures 2 and 3 show the changes in consistency coefficient (K) and flow behaviour index (n) of noni juice with temperature. The consistency coefficient decreased with increasing temperature while the flow behaviour index increased. For the studied concentrations and the range of pasteurisation temperature investigated, noni juice retain

4 Food Bioprocess Technol (2011) 4: their shear-thinning (pseudoplastic) characteristic as indicated by the values of n which were less than 1 ( ). Similar results were reported for Roselle extract at all concentrations and temperatures (Hasaan and Hobani 1998), pink guava juice (Zainal et al. 2000), yellow mombin juice (Assis et al. 2006), and macromolecular suspensions, such as guar and xanthan gums (Queiroz and Fontes 2008). The flowing behaviour index decreased when total soluble solids increased. This tendency is similar to low pulp concentrated orange juice (Vitali and Rao 1984), apricot puree (Duran and Costell 1982), and yellow mombin juice (Assis et al. 2006). The increased in solid concentration also increased the consistency coefficient, but decreased the flow behaviour index. The viscosity of a solution is a function of the intermolecular forces and water solute interactions that restrict the molecular motion. These forces are affected by changes in both concentration and temperature. When a solution is heated, the viscosity decrease since thermal energy of the molecules increases and the intermolecular distances increase due to thermal expansion (Constenla et al. 1989). The changes in rheological properties of noni juice as a function of temperature are in agreement with raspberry and tomato juice as reported by Ibarz and Pagan (1987) and Filkova et al. (1987), respectively. Decrease in consistency coefficient of guava puree, orange juice, and clarified apple juice with increasing temperature has also been reported by Vitali and Rao (1982), Ibarz et al. (1994) and Constenla et al. (1989), respectively. When the solution is heated, the viscosity decreases as the thermal energy of the molecules increases, and the intermolecular distances increase due to thermal expansion (Guimaraes et al. 2009). In addition, it is important to note that the consistency coefficient decreased as solid concentration decreased. When the solid concentration increases, the viscosity increases because of the increase in hydrogen bonding with hydroxyl groups and the distortion in the velocity pattern of the liquid by hydrated molecules of the solute. The intermolecular distance is also a factor that affects the viscosity inversely proportional to it due to changing temperatures (Guimaraes et al. 2009). This decrease in the consistency coefficient, would agree with the findings by Vitali and Rao (1982), Bayindirli (1993), and Ibarz et al. (1994) who showed that the apparent viscosity decreased as the concentration of the guava puree, grape juice, and orange juice decreased, respectively. A decrease in consistency coefficient will increase the flowing rate of juice due to less resistance flowing (Earle 1985). The increase of the flowing rate of juice means that heating and holding time in flowing lines during pasteurisation at recommended operating variables will be shorter. The effect of temperature on the consistency coefficient and flow behaviour index can be described by Arrhenius equation (Ibarz et al. 1994). The Arrhenius model is quite applicable to nonpolar liquids. Nevertheless, in fluids constituted of molecules that interact through hydrogen bridges, dipoles, or covalent bonds, for instance, a deviation from this model may occur, mainly, due to temperature influence. Although fluid foods could hardly be considered as constituted by nonpolar molecules, the Arrhenius model has been often and successfully applied to describe the temperature dependence of rheological properties of fluid foods, such as fruit juices (Telis-Romero et al. 1999), coffee extract (Telis-Romero et al. 2001), honey (Yanniotis et al. 2006), aqueous carbohydrate solutions (Telis et al. 2007), and grape pekmez (Kaya et al. 2008). As can be seen in Figs. 2 and 3, the changes in K and n for noni juice also well fitted the modified Arrhenius equation with coefficient of determination (R 2 ) of and , respectively. The models describing the Fig. 2 Effect of temperature and solid concentration on consistency coefficient of noni juice TSS = 10 Brix Equation Temperature, o C

5 1486 Food Bioprocess Technol (2011) 4: Fig. 3 Effect of temperature and solid concentration on flow behaviour index of noni juice Flow Behaviour Index TSS = 10 Brix Equation Temperature, o C Fig. 4 Effect of temperature and solid concentration on density of noni juice TSS= 10 Brix Equation Temperature, ( o C) Fig. 5 Effect of temperature and solid concentration on thermal conductivity of noni juice TSS=10 Brix Equation Temperature, ( o C)

6 Food Bioprocess Technol (2011) 4: relationships between the rheological properties of two different concentrations of noni juice and temperature can be given as: Consistency coefficient: a 3 K ¼ a 1 : exp a 2 :C þ ðt þ 273Þ ð7þ with a 1 =0.0053, a 2 = , and a 3 = , respectively. Flow behaviour index: b 3 n ¼ b 1 : exp b 2 :C þ ðt þ 273Þ with b 1 =0.1984, b 2 =0.1275, and b 3 = , respectively. Effect of Temperature and Solid Concentration on Density ð8þ Figure 4 shows the effect of temperature and solid concentration on juice density. The density of noni juice increased with increasing solid concentration, but decreased with increasing temperature. This result is in agreement with pectinised and clarified pear juice (Ibarz and Miguelsanz 1990), grape juice (Bayindirli 1993), clarified apple juice (Constenla et al. 1989), clarified peach and orange juice (Ramos and Ibarz 1998), guava juice (Shamsudin et al. 2005), and clear grape juice (Zuritz et al. 2005). In addition, Magerramov et al. (2008) also reported similar results for melon, cherry plum, plum, and tangerine juices. They also further mentioned that fruit juice behaviour is like pure water behaviour, because water is the major component of all fruit juices. The relationship between the density of noni juice and temperature and solid concentration can be represented by the equation below: r ¼ c 1 þ c 2 :C þ c 3 :T ð9þ with c 1 = , c 2 =1.3476, and c 3 = , respectively. The coefficient of determination (R 2 ) obtained from this equation was At a fix pump pressure, decrease in density will cause increase in volumetric flow rate of the juice due to reduction in weight. Shorter heating and holding times in flow lines as required during pasteurisation could be achieved at low density juice. Effect of Temperature and Solid Concentration on Thermal Conductivity Figure 5 shows the thermal conductivity of noni juice at different temperature and solid content. Thermal conductivity decreased slightly with increasing solid concentration as reported for tomato juice (Filkova et al. 1987). In contrast to that, the thermal conductivity increased with increasing temperature. A similar result was reported by Telis-Romero et al. (1998) for thermal conductivity of orange juice. This result showed that the thermal conductivity of a food product is a function of water content and structure as reported by Heldman and Lund (1992). Based on Fig. 5, a regression equation correlating temperature and solid concentration with thermal conductivity of noni juice is proposed as: k ¼ d 1 þ d 2 :C þ d 3 :T ð10þ with d 1 = , d 2 = , and d 3 =1.0279, respectively. The coefficient of determination (R 2 ) obtained from this equation was Conclusions From this study, it was found that density, thermal conductivity, and flow characteristics of noni juice were temperature- and concentration-dependent. However, in order to obtain clearer thermal conductivity dependency on concentration, it is recommended that the solid concentration range must be widened. The regression equations or models proposed in this study are capable to simulate the physical properties of the juice during pasteurisation. Acknowledgements The authors would like to express their gratitude to Diponegoro University for the financial support of this research project through the Faculty of Engineering Cluster Research Grant 2008, contract number 3993/H7.1.31/PG/2008. References Alvarado, J. D., & Romero, C. H. (1989). Physical properties of fruits I. density and viscosity of juices as functions of soluble solids content and temperature. Latin American Applied Research, 19, Assis, M. M. M., Lannes, S. C. S., Tadini, C. C., Telis, V. R. N., & Telis-Romero, J. (2006). Influence of temperature and concentration on thermophysical properties of yellow mombin (Spondias mombin, L.). European Food Research Technology, 223, Bayindirli, L. (1993). Density and viscosity of grape juice as a function of concentration and temperature. Journal of Food Processing and Preservation, 17, Bellet, D., Sangelin, M., & Thirriot, C. (1975). Determination des Proprietes themophysiques de liquides non-newtniens a l áide d une cellule a cylindres coaxiaux. International Journal of Heat Mass Transfer, 18(10), Constenla, D. T., Lozano, J. E., & Crapiste, G. H. (1989). Thermophysical properties of clarified apple juice as a function of concentration and temperature. Journal of Food Science, 54 (3), Dixon, A. R., McMillen, H., & Etkin, N. L., (1999). Ferment this: The transformation of Noni, a traditional Polynesian medicine (Morinda citrifolia, Rubiaceae). Ecological Botony, (53),

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