Effects of different drying techniques of stigma on humidity content, drying time and qualitative criteria of saffron

Saffron is considered to be one of the most expensive agricultural products in the world. Saffron specific compounds including crocin, picrocrocin and safranal. Different drying methods, not only differ in energy consumption but also, influence the chemical and sensory properties of saffron. Accordingly, the current study was aimed to investigate the effect of different drying techniques on quality of saffron. The experiment was laid out as a completely randomized design with four replications at Ferdowsi University of Mashhad Faculty of Agriculture, Mashhad Iran in 2015, 2016 and 2017. Four different drying techniques i.e. traditional technique (shade dried at laboratory temperature), oven (at 40, 60 and 80° C), microwave (at 200, 400 and 600 watts), freeze (at -18° C for 5 h and then heating at 60±5 with evacuation intervals of 15, 10, 10 and 10 minutes) were considered as the treatments. Chemical tests were performed according to ISO 3632-2 (E) 1993 and safranal was measured using chromatography. The results indicated that chemical properties of stigma including moisture percentage, total ash, insoluble ash in acid and soluble extract in cold water and nitrogen are in accordance with Iranian National Standards. The maximum picrocrocin (140.66%) and safranal (42.64%) were obtained when stigmas were dried using microwave technique at 600 w. The maximum crocin percentage was related to freezing technique (299.64). The maximum (245.91) and minimum (88.15) safranal weight percentage were observed when freezing and traditional techniques were practiced. According to the results, although preserving all the qualitative features of saffron during drying process seems difficult, in order to achieve a higher level of quality, controlled methods such as microwave or freezing techniques are recommended.