Studying the thin‐layer drying kinetics and qualitative characteristics of dehydrated saffron petals

Saffron petal is mostly considered the waste part of harvested saffron flower which may have a substantial potential in industry in terms of color and valuable contents. Hence, the primary objective of the present study was to determine the most appropriate semi‐empirical kinetic model for describing the given drying process including three temperatures (40, 50, and 60 °C) and air velocity levels (0.7, 1.4, and 2.1 m s−1), and the secondary was to investigate the effects of thin layer drying on qualitative characteristics of saffron petals (Total anthocyanin content and the antioxidative activity) as decisive factors on its favorability to food industry. The results also showed that increasing air temperature from 40 to 60 °C could remarkably reduce the drying time from 92 to 15 min while the air velocity increase within two steps from 0.7 to 1.4 m s−1 and 1.4 to 2.1 m s−1 was accompanied by two opposite trends, that is, increase and decrease in drying time, respectively. Besides, the amount of moisture loss of saffron petals during drying showed that kinetic parameters like effective moisture diffusivity, energy of activation and Arrhenius constant were all affected by both factors of temperature and velocity while the ranges of changes were gained 7.7×10−12– 5.1×10−11 m2 s−1, 4.43–6.28 kJ mol−1, and 1.35×10−8– 3.1×10−7 m2 s−1, respectively. In the meanwhile, Logarithmic model was also found as the best model fitted to most experimental data. The experimental results revealed that the given qualitative characteristics were much better preserved at 50 °C and 1.4 m s−1 combination. PRACTICAL APPLICATIONS: Drying or “dehydrating” food is a one of the widely used and oldest methods of food preservation that removes enough moisture from the food so bacteria, yeast and molds cannot grow. Besides, drying process has had a significant effect on the drying kinetics and quality of the dried product Saffron petals is a rich source of antioxidant which is also regarded as a natural food colorant and a healthy substitute for the chemical ones. Besides, it is reported that around 12,000 ton petals of saffron is annually produced in Iran which is mostly considered waste which can be returned to industry and production. Meanwhile, due to high moisture content, this study aimed to investigate the effect of thin layer drying on qualitative characteristics of saffron petals, anthocyanin content, and the antioxidative activity, and also to determine the most appropriate semi‐empirical kinetic model for describing the drying process.