Infrared thin layer drying of saffron (Crocus sativus L.) stigmas: Mass transfer parameters and quality assessment

Saffron is the most precious and expensive agricultural product. A dehydration treatment is necessary to convert Crocus sativus L. stigmas into saffron spice. To the best of our knowledge, no information on mass transfer parameters of saffron stigmas is available in the literature. This study aimed at investigating themoisture transfer parameters and quality attributes of saffron stigmas under infrared treatment at different temperatures (60, 70,., 110 degrees C). It was observed that the dehydration process of the samples occurred in a short accelerating rate period at the start followed by a falling rate period. The effective moisture diffusivity and convective mass transfer coefficient were determined by using the Dincer and Dost model. The diffusivity values varied from 1.1103 x 10(-10) m(2) .s(-1) to 4.1397 x 10(-10) m(2) . s(-1) and mass transfer coefficient varied in the range of 2.6433 x 10(-7)-8.7203 x 10(-7) m.s(-1). The activation energy was obtained to be 27.86 kJ.mol(-1). The quality assessment results showed that the total crocin content increased, when the temperature increased up to 90 degrees C but, in higher temperatures, the amount of crocin decreased slightly. The total safranal content of the samples decreased slightlywhen drying temperature increased from 60 degrees C to 70 degrees C and then continuously increased up to 110 degrees C. Also, the amount of picrocrocin increased from 83.1 to 93.3 as the drying temperature increased from 60 degrees C to 100 degrees C. (C) 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.