INFLUENCE OF THICKNESS ON THE DRYING OF PAPAYA PUREE (Carica papaya L.) THROUGH REFRACTANCE WINDOWTM TECHNOLOGY
Palabras clave:
drying, papaya, refractance window, diffusion coefficient, mathematical modeling (es)
INFLUENCE OF THICKNESS ON THE DRYING OF PAPAYA PUREE (Carica papaya L.) THROUGH REFRACTANCE WINDOWTM TECHNOLOGY
INFLUENCIA DEL ESPESOR EN SECADO DE PURÉ DE PAPAYA (Carica Papaya L.) POR TECNOLOGÍA DE VENTANA DE REFRACTANCIA®
MARÍA U. OCORÓ-ZAMORA
MSc. Young Researcher, School of Food Engineering, Universidad del Valle, Cali-Colombia, mariaurany@gmail.com
ALFREDO A. AYALA-APONTE
PhD. Professor, School of Food Engineering, Universidad del Valle, Cali-Colombia, alfredo.ayala@correounivalle.edu.co
Received for review August 15th, 2012, accepted April 26th, 2013, final version May, 20th, 2013
ABSTRACT: The aim of this study was to evaluate the influence of sample thickness (2, 3 and 4 mm) on the drying kinetics, water activity (aw) and color (∆E) of papaya puree slices processed through Refractance WindowTM technology (RW™). Additionally, the water diffusion coefficient (Deff) was evaluated taking into account the shrinkage effect. The experimental values of moisture were fitted using Newton's and Midilli's models. The results showed that the lower the thickness, the faster the drying, the lower the values of aw and the higher the ∆E. The samples reached 0.0652, 0.1132 and 0.2624 g water/ g dry solid in 60 min for 2, 3 and 4 mm slices, respectively. Midilli's model was the most appropriate to predict the experimental curves of papaya drying through RW™. Deff decreased at a lower thickness and its order of magnitude was of 10-10 m2/s.
KEYWORDS: drying, papaya, refractance window, diffusion coefficient, mathematical modeling.
RESUMEN: El objetivo de este trabajo fue evaluar la influencia del espesor de las muestras (2, 3 y 4 mm) sobre las cinéticas de secado, actividad de agua (aw) y color (∆E) de rodajas de puré de papaya procesadas por tecnología de ventana de refractanciaTM (RW™). Adicionalmente se evaluó la difusividad del agua (Deff) teniendo en cuenta el encogimiento. Los datos de humedad se ajustaron mediante los modelos de Newton y Midilli. Los resultados mostraron que a menor espesor el secado fue más rápido, los valores de aw fueron menores y los ∆E superiores. Las muestras alcanzaron 0.0652, 0.1132 y 0.2624 g agua/ g sólido seco en 60 min para rodajas de 2, 3 y 4 mm, respectivamente. El Modelo de Midilli fue el más apropiado para predecir las curvas de secado de papaya por RW™. Deff disminuyó a menor espesor y su orden de magnitud fue de 10-10 m2/s.
PALABRAS CLAVE: secado, papaya, ventana de refractancia, coeficiente de difusión, modelamiento matemático.
1. INTRODUCTION
Papaya is a tropical fruit which originated from Mexico and Central America, and it is a good source of vitamins (C, A, B1, B2 and carotenoids) [1, 2]. Papaya is highly perishable, mainly due to its high moisture content (between 80 and 85% wb), so it is important to find alternatives for its preservation and/ or processing [3-5].
Drying is one of the most commonly-used processes for food preservation due to the significant reduction of water activity and consequently, the reduction of microbiological activity and physical and chemical changes during storage of the product [6]. During drying, foods undergo changes in volume, shape, porosity and density that can cause shrinkage or structural collapse, thus affecting the quality of the final product [7]. Therefore, changes in volume should be considered for the modeling of mass transfer during a drying process [7-8].
Several methods of food drying have been developed (spray drying, tray drying, freeze drying, among others) but none provide economical and high quality products [9]. Freeze drying is considered one of the best food processing methods to produce high-quality dehydrated food, but it is a costly and time-consuming process.
Refractance WindowTM (RW™) is an innovative drying technology developed by MCD Technologies Inc. (Tacoma, Washington, USA), featuring short drying times, low energy consumption, and high-quality of products [10]. This technology is used for drying of fruit puree, where the puree is spread on a plastic belt that moves over a reservoir of hot water (temperature below the boiling point), with infrared radiation from the water passing through the belt and causing the drying of the material [11].
As RW™ is a relatively novel technology, there are not many scientific publications related to the influence of puree thickness, and water temperature, on product characteristics [9-16].
The aim of this study was to evaluate the influence of samples thickness (2, 3 and 4 mm) on the drying kinetics, water activity (aw) and color (∆E) of papaya puree slices dried through the RW™ technique. Additionally, the water diffusion coefficient was evaluated, taking into account the shrinkage effect.
2. MATHERIALS AND METHODS
2.1. Raw material and experimental design
Papaya fruits were obtained at a local market (Cali-Colombia) and were selected with uniform soluble solids content (10 - 12º Brix). These were prime-quality samples, according to the Colombian Technical Standard NTC 1270 [17]. The fruits were washed, peeled (using a stainless steel knife) and cut into two pieces to remove the seeds. The fruit puree was obtained with a food processor (Oster, 3167, USA). Preformed plastic molds were used to obtain puree slices of 2, 3 or 4 mm of thickness and 30 mm in diameter.
The slices were dried in a prototype designed to reproduce the RW™ principle (Figure 1). This consists in a tank filled with water (length: 0.6 m, width: 0.4 m, depth: 0.1 m), where a polyester membrane (MylarTM type - transparent to infrared radiation) slides over the water surface at a speed of 0.001 m/min. The water was recirculated at a rate of 2.74 L/min in order to recover the unused heat. The water temperature was set up at 70°C.
A completely randomized design was carried out considering the thickness of the puree slices (2, 3 and 4 mm) and the drying time (0, 10, 20, 30, 60, 90, 120 and 180 min) as the experimental factors. The response variables were moisture content (MC), water activity (aw), total color difference (∆E), apparent density (rat), and volume (V). Experiments were conducted in triplicate.
2.2. Physicochemical analysis
The MC was determined by drying the samples in a vacuum oven until constant weight at 60°C (AOAC, 1980) [18]. The aw was measured with a dew-point hygrometer (Decagon, AquaLab CX-1, USA) with a sensitivity of 0.0001.
The color was measured between 400-780 nm, employing a spectrocolorimeter (Hunter-Lab, ColorFlex, USA) and using as standard the illuminant D65 and the 10º observer in order to obtain the color coordinates CIE-L*a*b*. ∆E was determined through (1):
The rat of the samples was determined by means of the volume displacement method, using a pycnometer and distilled water at 20±٠.٣°C as the displacement medium. The V of the slices was calculated from rat data.
2.3. Mathematical modeling
The drying kinetics were fitted using Newton's (2) and Midilli's (3) models, widely used for modeling moisture ratio (MR) in biological materials [19-21].
where k, a, n and b are parameters of the models and t is the drying time.
MR is defined in accordance with (4).
where Xt is the moisture content at a given time, Xe is the equilibrium moisture content and X0 is the initial moisture content (g water/g dry solid). However, MR was simplified to (5), taking into account that the RW™ equipment used for the experiments does not control the relative humidity of air in contact with the material [21-23].
The analytical solution of Fick's second law was used in order to determine the effective diffusion coefficient (Deff), considering the geometry of a semi-infinite sheet with thickness l and assuming that the drying process is controlled by internal moisture diffusion in an axial direction. The analytical solution is given by (6) [24], which is valid only for the falling rate drying period.
To take shrinkage into account, the sample thickness must be considered as a function of time l(t)(7)[25]:
where mt is the mass at a given time (g), rat is the apparent density at a given time (g/cm3) and R is the ratio of the papaya slices, equivalent to 0.015 m. Deff values were calculated with and without considering shrinkage.
2.4. Statistical Analysis
The order of the experiments and the effect of thickness on the response variables were determined by means of the Minitab statistical program (version 15.1.20.0, 2007), for a significance of 0.05 and a confidence interval of 95% (p<0.05). Regressions to estimate the parameters of Newton's and Midilli's models were performed, using the Polymath 5.0 (version 5.1, 2000) statistical software. The fitting quality of the experimental data to the models was assessed using the correlation coefficient (R2), reduced Chi-square (χ2), and the Root Mean Square Error (RMSE). These statistical parameters were calculated using equations (8), (9) and (10) [26], respectively. The highest values of R2 and the lowest values of χ2 and RMSE were taken as the optimum criteria.
where N is the number of observations, z is the number of model parameters, MRexp is the experimental moisture ratio, and MRpre is the predicted moisture ratio.
3. RESULTS AND DISCUSSION
3.1. Moisture content (MC)
The initial MC of papaya puree was 8.2262 ± 0.4519 g water/g dry solid. The MC decreased faster at a lower thickness; the samples of 2 mm reached 0.0652 g water/g dry solid in 60 min, while those of 3 and 4 mm reached 0.1132 and 0.2624 g water/g dry solid, respectively. Figure 2 shows MC variation of papaya samples during the drying time.
Thinly sliced samples dried faster due to the reduced distance the water travels in order to be extracted [27]. Similar results were observed during drying of mango [16] and orange [28] by RW™, and during convective drying of eggplant [29], papaya and garlic [30]. According to Geankoplis (1993) [31], the drying time is directly proportional to the weight of dry solid, which increases with the increasing of thickness. The ANOVA (Analysis of Variance) showed a significant effect (p<0.05) of thickness and drying time on MC of papaya samples.
3.2. Water activity (aw)
Thickness affected the aw of the samples significantly (Figure 3). Findings showed that the lower the thickness, the lower the value of aw, at a specific time. Similar results were obtained during drying of mango using the RW™ technique [16].
After 60 min of drying, samples of 2 and 3 mm reached values of aw below 0.6, but 2 mm samples reached the lowest value (0.41); these results indicate the growth restriction of pathogenic microorganisms such as fungi, yeasts, and bacteria [32]. After 90 min of drying, these samples present values of aw below 0.4, which are characteristic of highly stable food during storage [33]. This result is relevant for the preservation of papaya because of its high susceptibility to mold growth [34]. The ANOVA evidenced a significant effect (p<0.05) of thickness and drying time on the aw of papaya samples.
3.3. Color
Figure 4 presents the values of ∆E of papaya samples during the drying process. For the three sample thicknesses investigated, it can be observed that ∆E increases until about 60 min of drying and subsequently stabilizes. This behavior shows the ability of RW™ technique to self-regulate and protect the characteristics of the puree at low moisture content [35]. The influence of thickness on ∆E is also observed, obtaining a higher value for the samples of lower thickness. This result is due to the fact that thinner samples reach higher internal temperatures which causes further degradation of the papaya carotenoids (licopene, ß-criptoxanthin, ß-carotene). Ahmed et al. (2002) [36] report that the change in color of papaya puree is a direct consequence of the change in the carotenoids; the authors also point out that the color change reaction has first order kinetics, where the rate constant depends on the temperature and follows the Arrhenius relationship.
The ANOVA showed that thickness and drying time had a significant influence (p<0.05) on the ∆E of papaya puree slices.
3.4. Mathematical modeling of drying kinetics
Table 1 shows the estimated kinetic parameters of Newton and Midilli's models, including criteria to evaluate the fitting quality.
It is observed that the parameter k increases at a lower thickness of the samples, having a higher value for the samples of 2 mm with 7.5617x10-2 (min-1). The variable k is often temperature dependent, consequently, an increase in k is related to an increase in drying temperature [37]. Generally, higher drying temperatures resulted in steeper curves and shorter drying times [38]. In this study, the temperature was constant (70ºC), therefore, this behavior is probably due to the fact that thinner samples reached higher temperature at their geometrical center as a result of the smaller mass per unit of surface area.
Both proposed models showed a good fit of the experimental values, nevertheless, Midilli's model was the one with the best fit (Figure 5) corresponding to the highest values of correlation coefficient and the lowest values of χ2 and RMSE.
Some researchers have found that Midilli's model accurately characterized the drying behavior of different foods, as in apple drying with infrared rays [19] and red pepper drying by combining hot air and ultrasound [21].
3.5. Effective diffusion coefficient (Deff)
Deff was calculated for the first falling rate drying period using the first term of the analytical solution of Fick's second law, which was the most significant. For this calculation, shrinkage or volume change (see Figure 6), of the slices as a function of drying time was considered, which was calculated from rat (values not shown). According to the results, thickness influenced volume change during drying; specifically, the thicker the sample, the smaller the changes (4 mm samples showed the highest values of V).
Table 2 shows the influence of thickness and volume change on Deff of papaya puree slices during drying, which have a similar magnitude order to those reported in drying of papaya by convection [39] and treatment by osmotic dehydration [5].
It can be seen that Deff and Deff* are higher when puree thickness increases, because the thicker samples exhibit less shrinkage for a fixed time (Figure 6), thus, significantly facilitating diffusion. Similar results were obtained in convective drying of papaya slices [30], mango drying by RW™ [16], and sun and convective drying of grape products [27].
Table 2 also shows that the diffusion coefficient values corrected by volume (Deff*) were lower than the uncorrected values (Deff), since food shrinkage modifies the distance required for the movement of water molecules [40]. The diffusion coefficient is overestimated between 58.78 and 90.60%, when volume correction is not taken into account.
4. CONCLUSION
Thickness of papaya puree significantly influenced drying kinetics, water activity and the color of the product; the lower the thickness, the faster the drying, the lower the aw and the higher the ∆E. Midilli's model was the most appropriate to predict the experimental drying curves of papaya puree processed by RW™. The diffusion coefficient was higher when not considering shrinkage. These findings show that the RW™ technique is highly suitable for papaya drying; it makes it possible to dry the product reaching a low moisture content in shorter times, reducing the aw to values below 0.4 and preserving a similar color.
REFERENCES
[1] De Oliveira, J.G. and Vitória, A.P., Papaya: Nutritional and pharmacological characterization, and quality loss due to physiological disorders. An overview, Food Res Int., 44 (5), pp. 1306-1313, 2011.
[2] Gayosso, L.E., Yahia, E.M. and González, G.A., Identification and quantification of phenols, carotenoids and vitamin C from papaya (Carica papaya L., cv. Maradol) fruit determined by HPLC-DAD-MS/MS-ESI, Food Res Int, 44 (5), pp. 1284-1291, 2011.
[3] Fernandes, F.A.N., Rodrigues, S., Gaspareto, O.C.P. and Oliveira, E.L., Optimization of osmotic dehydration of papaya followed by air drying, Food Res Int, 39 (4), pp. 492-498, 2006.
[4] El-Aouar, Â.A., Moreira Azoubel, P. and Xidieh Murr, F.E., Drying kinetics of fresh and osmotically pre-treated papaya (Carica papaya L.), J Food Eng, 59 (1), pp. 85-91, 2003.
[5] Rodrigues, A.C.C., Cunha, R.L. and Hubinger, M.D., Rheological properties and color evaluation of papaya during osmotic dehydration processing. J Food Eng, 59 (2-3), pp. 129-135, 2003.
[6] Mayor, L. and Sereno, A.M., Modelling Shrinkage during convective drying of food materials: a review. J Food Eng, 61 (3), pp. 373-386, 2004.
[7] Khalloufi, S., Almeida-Rivera, C. and Bongers, P.A., Theoretical model and its experimental validation to predict the porosity as a function of shrinkage and collapse phenomena during drying. Food Res Int, 42 (8), pp. 1122-1130, 2009.
[8] Mayor, L., Moreira, R. and Sereno, A.M., Shrinkage, density, porosity and shape changes during dehydration of pumpkin (Curcubita pepo L.) fruits, J Food Eng, 103 (1), pp. 29-37, 2011.
[9] Abonyi, B.I., Tang, J. and Edwards, C.G., Evaluation of energy efficiency and quality retention for the refractance windowTM drying system. [Research Report]. Pullman, Washington D.C: U S. Washington State University, 1999.
[10] Topuz, A., Feng, H. and Kushad, M., The effect of drying method and storage on color characteristics of paprika. Food Sci Tech, 42 (10), pp. 1667-1673, 2009.
[11] Abonyi, B.I., Feng, H., Tang, J., Edwards, C.G. and Chew, B.P, et al. Quality retention in strawberry and carrots purees dried with refractance windowTM system. J Food Sci, 67 (3), pp. 1051-1056, 2002.
[12] Topuz, A., Dincer, C., Özdemir, K.S., Feng, H. and Kushad, M., Influence of different drying methods on carotenoids and capsaicinoids of paprika (Cv., Jalapeno). Food Chem, 129 (3), pp. 860-865, 2011.
[13] Nindo, C.I., Feng, H., Shen, G.Q., Tang, J. and Kang, D.H., Energy utilization and microbial reduction in a new film drying system. J Food Process Pres, 27 (2), pp. 117-136, 2003.
[14] Nindo, C.I., Wang, S.W., Tang, J. and Powers, J.R., Evaluation of drying technologies for retention of physical quality and antioxidants in asparagus (Asparagus officinalis, L).Food SciTech, 36 (5), pp. 507-516, 2003.
[15] Nindo, C.I., Powers, J.R. and Tang, J., Influence of refractance window evaporation on quality of juices from small fruits. Food Sci Tech, 40 (6), pp. 1000-1007, 2007.
[16] Ochoa-Martínez, C.I., Quintero, P.T., Ayala, A.A. and Ortiz, M.J., Drying characteristics of mango slices using the Refractance WindowTM technique. J Food Eng, 109 (1), pp. 69-75, 2012.
[17] INSTITUTO COLOMBIANO DE NORMAS TÉCNICAS Y CERTIFICACIÓN (ICONTEC)., Norma Técnica Colombiana NTC 1270: Industria Alimentaria. Papaya, ICONTEC, Bogotá, 1993.
[18] AOAC., Official methods of analysis, 13th edition, Association of the Official Agricultural Chemists, Washington D.C, 1980.
[19] Togrul, H., Simple modeling of infrared drying of fresh apple slices. J Food Eng, 71 (3), pp. 311-323, 2005.
[20] Vega-Gálvez, A., Ayala-Aponte, A., Notte, E., De La Fuente, L. and Lemus-Moncada, R., Mathematical Modeling of mass transfer during convective dehydration of brown algae Macrocystis Pyrifera. Dry Technol, 26 (12), pp. 1610-1616, 2008.
[21] Schössler, K., Jäger, H. and Knorr, D., Effect of continuous and intermittent ultrasound on drying time and effective diffusivity during convective drying of apple and red bell pepper. J Food Eng, 108 (1), pp. 103-110, 2012.
[22] Togrul, I.T. and Pehlivan, D., Mathematical Modelling of solar drying of apricots in thin layers. J Food Eng, 55 (3), pp. 209-216, 2002.
[23] Togrul, I.T. and Pehlivan, D., Modelling of thin layer drying kinetics of some fruits under open-air sun drying process. J Food Eng, 65 (3), pp. 413-425, 2004.
[24] Crank, J., The mathematics of diffusion, Second edition, Clarendon Press, Oxford, 1975.
[25] Dissa, A.O., Desmorieux, H., Bathiebo, J. and Koulidiati, J., Convective drying characteristics of Amelie mango (Mangifera Indica L. cv. 'Amelie') with correction for shrinkage. J Food Eng, 88 (4), pp. 429-437, 2008.
[26] Kavak-Akpinar, E., Bicer, Y. and Cetinkaya, F., Modelling of thin layer drying of parsley leaves in a convective dryer and under open sun. J Food Eng, 75 (3), pp. 308-315, 2006]
[27] Maskan, A., Kaya, S. and Maskan, M., Hot air and sun drying of grape leather (pestil). J Food Eng, 54 (1), pp. 81-88, 2002]
[28] Viveros, J.G., Cano, C.A., Ayala, A.A. y Ochoa, C.I., Implementación de un método novedoso (Ventana de Refractancia) para reducir el tiempo de secado en alimentos sólidos. Aplicación en rodajas de naranja. Memorias VII Congreso Iberoamericano de Ingeniería de Alimentos (CIBIA VII). Bogotá, Colombia, Septiembre 2009.
[29] Ertekin, C. and Yaldiz, O., Drying of eggplant and selection of a suitable thin layer drying model. J Food Eng, 63 (3), pp. 349-359, 2004.
[30] Fernando, W.J.N., Ahmad, A.L., Shukor S.R, ABD and Lok, Y.H., A model for constant temperature drying rates of case hardened slices of papaya and garlic. J Food Eng, 88 (2), pp. 229-238, 2008.
[31] Geankoplis, C.J., Transport processes and unit operations. Third edition, Prentice-Hall International Inc, USA, 1993.
[32] Labuza, T.P. and Hyman, C.R., Moisture migration and control in multi-domain foods: Review. Trends Food Sci Tech, 9 (2), pp. 47-55, 1998.
[33] Singh, R.P. and Heldman, D.R., Introduction to food engineering, Second edition, Academic Press, Inc, USA, 1993.
[34] Beserra-Nogueira, S., Labate, C.A., Gozzo, F.C., Pilau, E.J., Lajolo, F.M., et al. Proteomic analysis of papaya fruit ripening using 2DE-DIGE. J Proteomics, 75 (4), pp. 1428-1439, 2012.
[35] Clarke, P.T., Refractance WindowTM-"Down Under". Proceedings of the 14th International Drying Symposium. Brazil, Vol B, pp. 813-820, Aug 2004.
[36] Ahmed, J., Shivhare, U.S. and Sandhu, K.S., Thermal degradation kinetics of carotenoids and visual color of papaya puree. J Food Sci, 67 (7), pp. 2692-2695, 2002.
[37] Vega-Gálvez, A., Miranda, M., Clavería, R., Quispe, I., Vergara, J. et al. Effect of air temperature on drying kinetics and quality characteristics of osmo-treated jumbo squid (Dosidicus gigas). J Food Sci Tech, 44 (1), pp. 16-23, 2011.
[38] Torres, R., Montes, E.J., Andrade, R.D., Perez, O.A. and Toscano, H., Drying kinetics of two yam (Dioscorea alata) varieties. Dyna. 79 (171), pp. 175-182, 2012.
[39] Kurozawa, L.E., Hubinger, M.D. and Park, K.J., Glass transition phenomenon on shrinkage of papaya during convective drying. J food Eng, 108 (1), pp. 43-50, 2012.
[40] Hernández, J.A., Pavón, G. and García, M.A., Analytical solution of mass transfer equation considering shrinkage for modeling food-drying kinetics. J Food Eng, 45 (1), pp. 1-10, 2000.
Cómo citar
IEEE
ACM
ACS
APA
ABNT
Chicago
Harvard
MLA
Turabian
Vancouver
Descargar cita
Visitas a la página del resumen del artículo
Descargas
Licencia
Derechos de autor 2013 DYNA
![Creative Commons License](http://i.creativecommons.org/l/by-nc-nd/4.0/88x31.png)
Esta obra está bajo una licencia internacional Creative Commons Atribución-NoComercial-SinDerivadas 4.0.
El autor o autores de un artículo aceptado para publicación en cualquiera de las revistas editadas por la facultad de Minas cederán la totalidad de los derechos patrimoniales a la Universidad Nacional de Colombia de manera gratuita, dentro de los cuáles se incluyen: el derecho a editar, publicar, reproducir y distribuir tanto en medios impresos como digitales, además de incluir en artículo en índices internacionales y/o bases de datos, de igual manera, se faculta a la editorial para utilizar las imágenes, tablas y/o cualquier material gráfico presentado en el artículo para el diseño de carátulas o posters de la misma revista.