Ph.D. Dissertation:

Design and fabrication of a fluidized bed dryer for drying of saffron petals and study on its performance and thermo-dynamical properties and also quality indicators of final product

Saffron is one of the most important agricultural products and export items in Iran. Saffron petals considered as waste during the harvesting process. In order to investigate the quantitative and qualitative changes of saffron petals during drying and design and construction of a suitable dryer to maintain quantitative and qualitative characteristics, a factorial experiment was conducted in Islamic Azad University (Sabzevar Branch), in 2018. Factors were drying air temperature (35, 45 and 55 °C), drying method (fixed bed, with air velocity equal to 0.2 m / s), semi-liquid bed (with air velocity equal to 0.7 m / s) and the fluid bed (with an air velocity of 1.7 m / s). MATLAB software was used for mathematical modeling of drying kinetics and the most suitable model was selected based on the highest R2 and the lowest SSE and RMSE. Methanolic extract was used to determine antioxidant activity, total phenolic compounds and free radical scavenging activity. The results showed that the highest drying time was obtained in the fixed bed method at 35 °C and the lowest time was obtained in the fluidized bed method at 55 °C. At 35 °C, the best semi-experimental model fitted for drying by the fixed bed method was the Page model, the semi-fluid bed was the modified Henderson and Pubis model, and the fluidized bed method was the logarithmic model. At 45 °C, the best semi-experimental model fitted to the fixed bed method was the Silva model, the semi-fluid bed method was the binomial model , and fluid bed method was the logarithmic model. But at 55 °C in the fixed bed method, Henderson and Pubis modified model, the semi-fluid bed, the binomial model and in the fluid bed method Henderson and Pubis model were the best models with the lowest amount of SSE and RMSE and the highest coefficient of determination (R2). Effective diffusion coefficient under the influence of temperature and speed of air in the dryer were inconsistent from 9.32776×10^(-11) to 3.5328×10^(-10) m2/s and in fixed bed method, 3.7583×10^(-10) to 2.455×10^(-9) m2/s in the semi-fluid bed method, and 5.0826×10^(-9) to 1.963×10^(-9) m2/s in the fluid bed method. Also, with increasing temperature and drying speed, the value of this coefficient was increased. Dried samples in fluidized bed method had the highest amount of phenolic compounds, the percentage of free radical scavenging, the amount of rehydrating, the amount of b *and ?E, the lowest amount of a * and bulk density, while the samples dried in the semi-bed, had the highest anthocyanin content, the lowest alcohol solubility, the highest a* and luminosity (L *), and the lowest ?E. In the fixed bed method, the samples had the highest solubility in water and the highest amount of ?E. The highest amount of anthocyanin compounds, the highest amount of b * and the lowest amount of brightness and the amount of a * were observed at drying in 35° C. The highest amount of phenolic compounds, free radical scavenging activity, solubility in water, the highest amount of a * and the lowest amount of b * were obtained in the samples dried at 45 °C. The highest rehydration, solubility in alcohol and the brightness and the lowest apparent density were obtained in samples dried at 55 °C. Overall, the results of this experiment showed that the use of 55 ° C temperature and fluidized bed method with better drying process parameters such as less time, lower activation energy(Ea) and effective moisture penetration coefficient can provide better results in maintaining Saffron petals compounds. In terms of qualitative characteristics, 35 °C temperature by the fluidized bed method and in terms of physical characteristics, 45 ° C temperature in the semi-fluidized bed method could introduced as the most appropriate drying method. In relation to product color changes, the product dried at 55 ° C by semi-fluidized bed method had he lowest ?E.

Keywords: Saffron petals, Drying kinetics, effective moisture penetration Coefficient, Activation energy