The effects of temperature, air speed and IR radiation on drying kinetics and some quality factors of saffron

Document Type : Research Article


1 PhD student, Department of Food Science and Technology, Ferdowsi University

2 Assistant Professor, Department of Food Science and Technology, Ferdowsi University

3 Associate Professor, Department of Biosystems Engineering, Ferdowsi University

4 Professor .Computer Engineering Department.Ferdowsi University


Saffron is a dry, red color of the Crocus Sativus L. It is the most expensive spice in the world. Drying is an important step in the process of saffron production. Drying causes physical, chemical and biochemical changes to achieve the desired properties of saffron. In this study, the kinetics of drying saffron stigma using a combined hot air-infrared dryer at three temperature levels of 40, 50 and 60°C and two hot air flow speeds of 0.3 and 0.6 m/s as well as an ordinary hot-air dryer using the same conditions were studied. The effect of the studied parameters on the amount of crocin, picocrocin and safranal and the microbial load of the final product were also investigated. The results showed that, the Midley model was found to be the best model in fitting data of both drying methods. Infrared irradiation and increased temperature and air velocity caused a dramatic reduction in the drying time of saffron. The infiltration coefficient ranged from 1.8003×10-08 to 2.38346×10-08 m2/s for the hot air-infra-red method and 5.07×10- 10 to 2.7892×10-09 m2/s for hot air drying. The amount of activation energy in the combination method of hot air-infrared  varied from 10.43 kJ/mol to 11.6 kJ/mol, and was obtained at 34.1 kJ/mol and 62.4 kJ/mol in hot-air drying. In terms of maintaining the color strength of saffron, the highest crocin was obtained when the combination of hot air-infrared at 50 ° C and 0.3 m / s was used with an average of   1%E440nm 278.5, which was the highest among all other treatments. According to the national standard of Iran, microbial tests were carried out including identification of E. coli, identification of enterococci, identification of sulfite reducing clostridia and counting mold and yeast on different treatments. No significant differences were observed between the treatments.

Graphical Abstract

The effects of temperature, air speed and IR radiation on drying kinetics and some  quality factors of saffron


  • Investigation of drying of Saffron stigma using combined hot air-infrared dryer.
  • Study on the effect of drying type on the amount of crocin, picocrocin and safranal and the microbial load of the final product.
  • Developing the best model to predict the drying kinetics of Saffron stigma


Main Subjects

[1] Masi, E., et al., PTR-TOF-MS and HPLC analysis in the characterization of saffron (Crocus sativus L.) from Italy and Iran. Food chemistry, 2016. 192: p. 75-81.
[2] Gresta, F., et al., Analysis of flowering, stigmas yield and qualitative traits of saffron (Crocus sativus L.) as affected by environmental conditions. Scientia horticulturae, 2009. 119(3): p. 320-324.
[3] Mazloumi, M., et al., Comparison of the Effects of Drying Processes: Vacuum Oven, Freeze, Solar and Microwave with Traditional Method on the Qualitative Characteristics of the Iranian Saffron. Pajoohandeh Journal, 2008. 13(3): p. 213-223.
[4]  امیدبیگى، ر.. ( 1390 ) تولید و فراورى گیاهان دارویى. جلد سوم. انتشارات آستان قدس رضوی ، ص 1-400.
[5] Husaini, A.M., et al., Saffron (Crocus sativus Kashmirianus) cultivation in Kashmir: Practices and problems. Functional Plant Science and Biotechnology, 2010. 4(2): p. 108-115.
[6] Kumar, D.P., H.U. Hebbar, and M. Ramesh, Suitability of thin layer models for infrared–hot air-drying of onion slices. LWT-Food Science and Technology, 2006. 39(6): p. 700-705.
[7] Mongpraneet, S., T. Abe, and T. Tsurusaki, Accelerated drying of welsh onion by far infrared radiation under vacuum conditions. Journal of Food Engineering, 2002. 55(2): p. 147-156.
[8] Pan, Z. and G.G. Atungulu, Infrared heating for food and agricultural processing. 2010: CRC Press.
[9] Akhondi, E., A. Kazemi, and V. Maghsoodi, Determination of a suitable thin layer drying curve model for saffron (Crocus sativus L) stigmas in an infrared dryer. Scientia Iranica, 2011. 18(6): p. 1397-1401
[10] Nadian, M.H., et al., Improvement of Kiwifruit Drying using Computer Vision System (CVS) and ALM Clustering Method. Drying Technology, 2016(just-accepted)
[11] Salehi, F., Kashaninejad, M., Sadeghi Mahoonak, A., and Ziaiifar, A.M. (2017). Kinetics Modeling of Thin-Layer Drying of Button Mushroom in Combined Infrared-Hot Air Dryer. Journal of Food Science and Technology, 13, 99-109 (in Farsi).
[12]  Salehi, F., Kashaninejad, M., and Asadi, A. (2016). Investigation of Mass Transfer Kinetics in  Combined Infrared-Hot Air Dryer for Eggplant slices. Food Innovation Technology, 7, 53-60 (in Farsi).
[13] Hosseini Ghaboos, S.H., Seyedian Ardabili, S.M., Kashaninejad, M., Asadi, G., and Alami, M. (2016). Mass transfer kinetics of combined infrared - hot air drying of Pumpkin. Journal of food technology and nutrition, 13, 5-16 (in Farsi).
[14] Taghinezhad, E. and V. Rasooli Sharabiani, The effect of combination dryer of hot air – infrared and microwave on some quality properties of parboiled rice. Innovative Food Technologies, 2017. 5(1): p. 25-38 (in Farsi).
[15] نادیان، ح. (1395). طراحی، ساخت و ارزیابی خشک کن هیبریدی هوای داغ- مادون قرمز برای فرآیند خشک کردن لایه نازک کیوی مبتنی بر ماشین بینایی و منطق فازی. پایان نامه دکتری مهندسی مکانیک بیوسیستم. دانشگاه فردوسی مشهد.
[16] ISO 3632-2, 2010. Saffron (Crocus sativus L.): Test Methods (2003 revised 2010).Switzerland:Geneva, International Standards Organization
[17] استاندارد ملی ایران (شماره5689)، 1388، میکروبیولوژی زعفران-ویژگیها، انتشارات موسسه استاندارد و تحقیقات صنعتی ایران.
[18] Wu, B., et al., Catalytic infrared and hot air dehydration of carrot slices. Journal of Food Process Engineering, 2014. 37(2): p. 111-121
[19] Alaei, B. and R.A. Chayjan, Modelling of nectarine drying under near infrared–Vacuum conditions. Acta Scientiarum Polonorum. Technologia Alimentaria, 2015. 14(1).
[20] Henderson, S.M. (1974). Progress in developing the thin layer drying equation. Transactions of the ASABE., 17, 1167–1172.
[21] Guarte, R.C. (1996). Modelling the drying behaviour of copra and development of a natural convection dryer for production of high quality copra in the Philippines. Ph.D. dissertation, 287. Hohenheim University, Stuttgart, Germany.
[22] Ali Reza, Y., N. Ghasemian, and A. Salari, Infrared drying kinetics study of lime slices using hybrid GMDH-neural networks. Innovative Food Technologies, 2017. 5(1): p. 91-105.
[23] Ertekin, C. and O. Yaldiz, Drying of eggplant and selection of a suitable thin layer drying model. Journal of food engineering, 2004. 63(3): p. 349-359.
 [24]  Karathanos, V.T. (1999). Determination of water content of dried fruits by drying kinetics. J. Food Eng., 39, 337-344.
[25] Midilli, A., Kucuk, H., Yapar, Z. (2002). A new model for single layer drying. Drying Tech., 20(7), 1503-1513.
 [26] Wang, C. Y.,  and Singh, R. P. (1978). A single layer drying equation for rough rice. ASABE., paper No. 3001.
 [27] Verma, L. R., Bucklin, R. A., Endan, J. B.,  and Wraten, F. T. (1985). Effects of drying   air parameters on rice drying models. Transactions of ASAE., 28: 296–301.
[28] Mortezapour, H., et al., Saffron drying with a heat pump–assisted hybrid photovoltaic–thermal solar dryer. Drying Technology, 2012. 30(6): p. 560-566.
 [29] Amiri Chayjan, R., Tabatabaei Bahrabad, S.M., Rahimi S.F. (2013). Modeling infrared-covective drying of pistachio nuts under fixed and fluidized bed conditions. J. Food Process. Preserv., pp 12083.
[30] Hebbar, H.U., Vishwanathan, K.H., Ramesh, M.N. (2004). Development of combined infrared and hot air dryer for vegetables. J. Food Eng., 65, 557–563.
[31] Karami, H., M. Rasekh, and Y. Darvishi, Effect of temperature and air velocity on drying kinetics and organo essential oil extraction efficiency in a hybrid dryer. Innovative Food Technologies, 2017. 5(1): p. 65-75. (In Farsi).
[32] Nadian, M.H., et al., Optimal pretreatment determination of kiwifruit drying via online monitoring. Journal of the Science of Food and Agriculture, 2016. 96(14): p. 4785-4796.
[33] Abbasi, S., Minaei, S. and Khoshtaghaza. M. H. (2014). Investigation of kinetics and energy consumption thin layer drying of corn. J. Agri. Machinery. 4(1), 98-107. (In Farsi).
[34] Tolaba, M. and C. Suarez, Simulation of the thin-layer drying of corn by means of the diffusional model. Lebensmittel-Wissenschaft+ Technologie= Food science+ technology, 1988.
[35] Ansari Far, M.H., et al., Investigation of Mazafati Dates Species Drying Kinetics and Effective Moisture Diffusivity under the Cabinet Solar Dryer. Food Science & Technology, 2016. 13(56): p. 125-141.
[36]  صفری, م., امیری چایجان، ر. و علائی، ب. (1396) مدل سازی برخی ویژگیهای مغز بادام در خشک‌کن پیوسته نیمه‌صنعتی. فصلنامه علوم و صنایع غذایی ایران, شماره 65 ،دوره 14، ص 37 - 25.
[37] Carmona, M., et al., Influence of different drying and aging conditions on saffron constituents. Journal of agricultural and food chemistry, 2005. 53(10): p. 3974-3979
[38]  آقائی, ز و همکاران. (1396) تأثیر روش‌های مختلف خشک‌کردن بر ویژگی‌های فیزیکوشیمیایی و حسی زعفران. فصلنامه علوم و صنایع غذایی ایران, شماره 65 ،دوره 14، ص 138 - 129.
[39]         Del Campo, C.P., et al., Effects of mild temperature conditions during dehydration procedures on saffron quality parameters. Journal of the Science of Food and Agriculture, 2010. 90(4): p. 719-725.
[40] Gregory, M.J., R.C. Menary, and N.W. Davies, Effect of drying temperature and air flow on the production and retention of secondary metabolites in saffron. Journal of agricultural and food chemistry, 2005. 53(15): p. 5969-5975.
[41] تسلیمی، ا. و همکاران. (1385) مقایسه اثرات فرآیندهای خشک کردن خورشیدی و خلاء با روش سنتی بر ویژگیهای زعفران. فصلنامه علوم و صنایع غذایی ایران, شماره 3 ،دوره 3، ص 17 - 9.
 [42] Atefi, M., et al., Effects of Freeze-drying processes on the qualitative characteristics of Iranian saffron. 2004.
[43] Azarpazhooh, E., A. Ehtiati, and P. Sharayei, Modelling the Chemical and Microbial Changes of Saffron Flower during Storage Using Artificial Neural Networks and Genetic Algorithm. Saffron agronomy and technology, 2016. 4(4): p. 279-289