جستجوی مقالات مرتبط با کلیدواژه « microwave dryer » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

In this research, investigation drying of four rice cultivars (Fajr, Taromi , Dom-siah and Neda) were done by microwave dryer and using ohmic pre-treatment. Three voltages of 125, 150, 175 volts were selected for the pre- treatment ohmic in three times 5, 10 and 15 min and the weight changing were measured and recorded. Finally, the samples placed in the microwave by power 600 watt and every two minutes until dry weight changes were measured. The results of the experiment were analyzed using response surface methodology and artificial neural network. Investigation on rice varieties in the ohmic process showed that Fajr variety had the highest water extraction and weight loss compared to other varieties (Taromi , Dom-siah and Neda) and during the pre-treatment process of ohmic and also during drying by the microwave, those had more moisture extracted. And after that, Tarom and Dom-Siah had the highest amount of moisture removal, Also the lowest moisture removal during the Ohmic heating and drying process were in Neda cultivar. In addition to weight loss in drying with a microwave dryer, Increasing voltage and ohmic time had higher moisture content than low voltage and low ohmic time and rice cultivar Fajr had more weight loss than other cultivars. Also, the predicted values of the response surface method (RSM) models and artificial neural network showed that the accuracy of the artificial neural network was 0.30 more than the predicted RSM numbers.

Drying process has a major effect on the color, odor and taste of fresh saffron. In this research, effect of traditional including sun and shadow drying and industrial drying methods such as electrical oven at 50 and 80 oC and microwave at 300 and 800 watt on the saffron of Kurdistan province for reaching the optimal condition, was investigated. Results showed that the drying methods had significant effects (p <0.01) on the physiochemical, microbial and sensory properties of saffron.  Crocin content for dried saffron with microwave at 800watt  that was about 171 and for 300 watt was 263.5 and with electric oven at 80 oC  was about 220.5,  respectively, not only were higher than the acceptable level according to national standard of Iran (220), but also they were significantly higher than other methods (p <0.01). The highest level of picrocrocin and safranal content were measured in samples dried with microwave at 800 watt (113.75, 30.25), electronic oven at 80 oC (115.5, 29.05), and shadow (105, 29.35), respectively. The lowest levels of crocin (146.5), picrocrocin (86.7) and safranal (23.4) were measured in sundried saffron. As microwave power level and electronic oven temperature increase, the crosin and picrocrocin contents of saffron increase significantly (p <0.01).  The lowest microbial load was found in saffron dried with microwave at 800 W and then sunlight (p <0.01). Overall, sensory attributes were ranked highest for the samples dried with microwave at 800 W and electronic oven at 80 oC, respectively. However, microwave drying at high power at 800 watt in comparison to other methods, could be the best drying method for saffron due to several advantages including reducing the drying time, keeping qualitative characteristics, decreasing microbial contamination and obtaining the highest score in organoleptic evaluation of dried saffron.

Paddy drying is one of the most important and critical post-harvest processes of rice in order to prevent the growth of germs and fungi; which enhances the product storage time. In this study, drying process of Tarom Hashemi was evaluated in a continuous band microwave dryer and in a domestic microwave dryer. The obtained results indicated that the moisture ratio decreased by increasing the paddy thickness from 6 to 18 mm and the microwave power levels from 10 to 30%, whereas the seed breakage increased. The drying ratio in the domestic microwave dryer was always less than that in the continuous band microwave dryer except at the 10% input power level, whereas the seed breakage percent was always more in the domestic microwave dryer in comparison with the continuous band microwave dryer. The results indicated that the moisture diffusion coefficient was larger in drying with continuous band microwave dryer in comparison with the domestic microwave dryer at 10% microwave power levels, whereas this coefficient was less at the 50% microwave power. As a final conclusion, the use of household microwave dryer for drying the paddy is not recommended due to high percentage of seed breakage. In contrast using a continuous band microwave dryer with low input power levels (e.g., 10%) is recommended on a large scale due to the rapid moisture reduction and low seed breakage percentage.