The Effect of Temperature and Air Velocity on Drying Kinetics of Pistachio Nuts during Roasting by using Hot Air Flow

Document Type : Research Article

Authors

• A. Dini ¹
• N. Sedaghat ¹
• S. M. A. Razavi ¹
• A. Koocheki ¹
• B. Malaekeh-Nikouei ²

¹ Department of Food Science, Engineering and Technology, Faculty of Agricultural, Ferdowsi University of Mashhad (FUM), Mashhad, Iran

² Nanotechnology Research Center, Mashhad University of Medical Sciences, Mashhad, Iran

https://doi.org/10.22067/jam.v7i2.55115

Abstract

Introduction
Pistachio nut is one of the most delicious and nutritious nuts in the world and it is being used as a saltedand roasted product or as an ingredient in snacks, ice cream, desserts, etc. The purpose of roasting is to promote flavour and texture changes in nuts that ultimately increase the overall palatability of the product.Roasting involves a number of physico-chemical changes, including heat exchange, chemical reactions and drying. Knowledge of desorption kinetics is essential to predict the behavior of the material during roasting process and to design roaster equipment.The main aim of this research was to evaluate suitable models for predicting moisture ratio, the effect of air temperature and velocity on the drying kinetics of pistachio nuts and obtain the effective diffusivity coefficient and activation energy in the drying process during the roasting of pistachio nuts.
Materials and Methods
Dried Ahmadaghaei pistachio nuts were supplied from Kashefan Kavir company (Doraj co.) in Rafsanjan. Pistachio nuts were soaked in 17% salt solution for 8 minute and roasting was investigated at air temperatures of 120,130, 145, 160 and 170 °C and air velocities of 0.6, 0.88, 1.3, 1.72 and 2 ms^-1. Five semi-theoretical and two empirical kinetic models were fitted to drying experimental data using nonlinear regression analysis techniques in the Curve Expert 2.2 computer program.
Results and Discussion
Tow-way ANOVA indicated that temperature and hot air velocity significantly affected the drying process during roasting of shelled pistachio nuts. The higher roasting temperatures and air velocities resulted in the higher drying rates. During first 10 min of roasting at constant air velocity of 1.3 ms^-1, 64.5%, 70.3%, 77.1%, 83.5%, 89.7% of the moisture were removed at roasting air temperatures of 120 °C, 130 °C, 145 °C, 160 °C, 170 °C, respectively. The high regression coefficients (R²>0.996) and low reduced chi-square (χ2), mean relative deviation modulus P (%) and Root Mean Square Error (RMSE) indicated that the Weibull models are suitable for predicting moisture ratio. Correlations of the Weibull model constants with the variables of temperature and velocity were determined. Additionally, effective diffusivity (Deff) determined by using Fick’s second law was varied from 4.418×10-09 to 2.648×10-08 m2s^-1 over the temperature and air velocity ranges. The lowest and highest Deff values were found for samples roasted at temperature of 120°C with air velocity of 0.6 m s^-1 and temperature of 170°C with air velocity of 2 ms^-1, respectively. Temperature dependence of the diffusivity coefficient was described by Arrhenius-type relationship. Also average activation energy was obtained 26.615 kJ mol^-1.
Conclusion
The results of this study showed that temperature and hot air velocity significantly affect the drying kinetics during roasting of pistachio nuts.The effective diffusion coefficient determined in this study was more than the limits specified in food products drying at lower temperatures and there was direct relationship between temperature and hot air velocity with effective diffusion. Activation energy was obtained close to some agricultural products.

Keywords

• Ahmadaghaei pistachio nuts
• Drying
• Effective diffusion
• Kinetics
• Roasting

20.1001.1.22286829.1396.7.2.7.4

References

1. Aghbashlo, M., M. H. Kianmehr, and S. R. Hassan-Beygi. 2010. Drying and rehydration characteristics of sour cherry (Prunus cerasus L.). Journal of food processing and preservation 34: 351-365.

2. Akpinar, E. K. 2006. Determination of suitable thin layer drying curve model for some vegetables and fruits. Journal of food engineering 73: 75-84.

3. Bruce, D. 1985. Exposed-layer barley drying: three models fitted to new data up to 150 C. Journal of Agricultural Engineering Research 32: 337-348.

4. Corzo, O., N. Bracho, and C. Alvarez. 2010. Weibull Model for thin-layer drying of mango slices at different maturity stages. Journal of food processing and preservation 34: 993-1008.

5. Corzo, O., N. Bracho, A. Pereira, and A. Vasquez. 2008. Weibull distribution for modeling air drying of coroba slices. LWT-Food Science and Technology 41: 2023-2028.

6. FAO. Food and Agriculture organization. 2014. Available at: http://faostat3.fao.org/browse/Q/QC/E

7. Fortes, M., and M. R. Okos. 1981. Non-equilibrium thermodynamics approach to heat and mass transfer in corn kernels. Transactions of the ASAE [American Society of Agricultural Engineers] 24: 761-0769.

8. Henderson, S. 1974. Progress in developing the thin layer drying equation [for maize]. Transactions of the ASAE 17:1167-1168.

9. Henderson, S., and S. Pabis. 1961. Grain drying theory I. Temperature effect on drying coefficient. Journal of Agricultural Engineering Research 6: 169-174.

10. Henderson, S., and S. Pabis. 1962. Grain drying theory: IV. The effect of air flow rate on the drying index. Journal of Agricultural Engineering Research 7: 85-89.

11. Hutchinson, D., and L. Otten. 1983. Thin‐layer air drying of soybeans and white beans. International Journal of Food Science & Technology 18: 507-522.

12. IPA (Iranian Pistachio Association website). 2015. Iran and US annual pistachio production comparison. Available at: http://iranpistachio.org/en/statistical-archive.

13. Karatas, S., and F. Battalbey. 1991. Determination of moisture diffusivity of pistachio nut meat during drying. Lebensmittel-Wissenschaft Technologie 24: 484-487.

14. Kashaninejad, M., A. Mortazavi, A. Safekordi, and L. Tabil. 2007. Thin-layer drying characteristics and modeling of pistachio nuts. Journal of Food Engineering 78: 98-108.

15. Kouchakzadeh, A. 2011. Moisture diffusivity of five major varieties of Iranian pistachios. American Journal of Food Technology 6: 253-259.

16. Madamba, P. S., R. H. Driscoll, and K. A. Buckle. 1996. The thin-layer drying characteristics of garlic slices. Journal of food engineering 29: 75-97.

17. Mohammadpour, V., M. H. Mosavian, and A. Etemadi. 2007. Determination of effective diffusivity coefficient and activation energy of shelled pistachio by using fluidized bed dryer. Archive of SID.

18. O’callaghan, J., D. Menzies, and P. Bailey. 1971. Digital simulation of agricultural drier performance. Journal of Agricultural Engineering Research 16: 223-244.

19. Overhults, D., G. White, H. Hamilton, and I. Ross. 1973. Drying soybeans with heated air. Transactions of the ASAE 16: 112-0113.

20. Özdemir, M., and Y. Onur Devres. 1999. The thin layer drying characteristics of hazelnuts during roasting. Journal of Food Engineering 42: 225-233.

21. Özdemir, M., and O. Devres. 2000. Analysis of color development during roasting of hazelnuts using response surface methodology. Journal of Food Engineering 45: 17-24.

22. Palipane, K. B., and R. H. Driscoll. 1994. The thin-layer drying characteristics of macadamia in-shell nuts and kernels. Journal of food engineering 23: 129-144.

23. Parti, M. 1993. Selection of mathematical models for drying grain in thin-layers. Journal of Agricultural Engineering Research 54: 339-352.

24. Rafiee, S., M. Sharifi, A. Keyhani, M. Omid, A. Jafari, S. S. Mohtasebi, and H. Mobli. 2010. Modeling effective moisture diffusivity of orange slice (Thompson Cv.). International Journal of Food Properties 13: 32-40.

25. Razavi, S. M., B. Emadzadeh, A. Rafe, and A. M. Amini. 2007. The physical properties of pistachio nut and its kernel as a function of moisture content and variety: Part I. Geometrical properties. Journal of Food Engineering 81: 209-217.

26. Rizvi, S. S. 1986. Thermodynamic properties of foods in dehydration. Engineering properties of foods 2:223-309.

27. Saklar, S., S. Katnas, and S. Ungan. 2001. Determination of optimum hazelnut roasting conditions. International Journal of Food Science & Technology 36: 271-281.

28. Tavakolipour, H. 2011. Drying kinetics of pistachio nuts (Pistacia vera L.). World Appl Sci J 12: 1639-1646.

29. Thompson, T., R. Peart, and G. Foster. 1968. Matllematical Simulation of Corn Drying A New Model. Transaction of the ASAE 11: 582-586.

30. Vega-Galvez, A., K. Di Scala, K. Rodriguez, R. Lemus-Mondaca, M. Miranda, J. Lopez, and M. Perez-Won. 2009. Effect of air-drying temperature on physico-chemical properties, antioxidant capacity, colour and total phenolic content of red pepper (Capsicum annuum L. var. Hungarian). Food Chemistry 117: 647-653.

31. Wang, C., and R. Singh. 1978. Use of variable equilibrium moisture content in modeling rice drying. Transactions of American Society of Agricultural Engineers 11: 668-672.

32. Xiao, H. W., C. L. Pang, L. H. Wang, J. W. Bai, W. X. Yang, and Z. J. Gao. 2010. Drying kinetics and quality of Monukka seedless grapes dried in an air-impingement jet dryer. Biosystems Engineering 105: 233-240.

33. ZaMan, W. Z., and T. A.Yang. 2013. Effect of Superheated Steam and Convection Roasting on Changes in Physical Properties of Cocoa Bean (Theobroma cacao). Food Science Technology Research 19 (2): 181-186.

34. Zhu, A., and X. Shen. 2014. The model and mass transfer characteristics of convection drying of peach slices. International Journal of Heat and Mass Transfer 72: 345-351.