عنوان مقاله [English]
Introduction Edible Button Mushroom (Agaricusbisporus) is one of the crops that is widely used today as a food source. Mushrooms after harvesting due to high humidity, high respiration rate, lack of cuticle and severe enzymatic activity, with persistence and quickly than other vegetables rot and discoloration begins immediately after harvest. To increase shelf life, edible mushroom must undergo processing processes. Drying is one of the most common methods of processing and preserving edible mushrooms. Vacuum-infrared drying is conducted by lowering moisture at low pressure to improve the quality of the high nutritional value product. Since button mushrooms have many applications due to their high nutritional value and medicinal uses, the best drying mode should be chosen to have the least negative effect on the quality properties and ingredients of the powder.
Materials and Methods Fresh edible button mushroom After washing were cut by a cutter at 5 mm thickness and dried using a vacuum-infrared dryer at three temperature levels of 40, 55 and 70 ° C and three vacuum pressure levels of 20, 40 and 60 kPa. Then the dried mushroom slices were milled and powdered using a mill machine for one minute. To homogenize the particle size, the button mushroom powder was sifted by a laboratory sieve with mesh No. 50 (cavity size 0.5 mm).In this study, the effect of vacuum-infrared drying variables including indoor air temperature and vacuum pressure on the thermal properties (effective moisture diffusion coefficient and drying energy consumption) of button mushroom and chemical (total phenol content) and qualitative (color indices as ΔL *, Δa * and Δb*) button mushroom powders were studied. Statistical analysis of data and optimization of drying process were performed using response surface methodology and central composite design (CCD). After determining the optimum point of vacuum-infrared dryer, loose and compacted bulk density, work index, Hassner ratio, angle of repose, and button mushroom powder slides were measured at optimum point and Finally the flow-ability of the edible button mushroom powder was determined.
Results and Discussion The results showed that as the chamber temperature increased, the rate of evaporation of tissue moisture increased, which resulted in a decrease in the drying time of the edible button mushroom thin layers with vacuum-infrared dryer. Effective moisture diffusion coefficient of drying of edible button mushroom thin films ranging from 1.8 ×10-9 m2/s (40 kPa pressure and temperature 40 °C) to 8.9×10-9 m2/s (20 kPa pressure and 70 °C temperature) was varied. The results showed that the air temperature of the drying chamber had a positive effect on the effective moisture diffusion coefficient. This is because increasing energy and heat consumption increased the activity of water molecules and, as a result, more moisture penetrated outside the product at higher temperatures. The maximum amount of specific energy consumption was 1269.73 MJ/kg (60 kPa pressure and 40 ° C) and the lowest amount was 408.36 MJ/kg (40 kPa pressure and 70 °C). The results showed that at constant pressure with increasing temperature, as the drying time decreased sharply, the amount of specific energy consumption also decreased. The phenolic content of button mushroom powder was in the range of 270 mg/g (20 kPa pressure and 40 ° C) and 1.3 mg/g (40 kPa pressure and 70 ° C). As the temperature increased, the total phenol content decreased. The results showed that increasing the temperature caused a greater difference between the color indices of L*, a * and b* of button mushroom powder than fresh mushroom. Increase in temperature caused more darkening (decrease in L* index), decrease in redness (decrease in index a*) and decrease in yellowness (decrease in index b*) of mushroom powder. In general, color indices were closer to the values of fresh fungal samples at low temperatures. The optimum drying point of button mushroom was obtained at 40° C and vacuum pressure of 40.823 kPa. The optimum value of the independent variables including effective moisture diffusion coefficient, specific drying energy consumption, total phenol content and final color indices of edible button mushroom ΔL*, Δa* and Δb* were 3.06×10-9 m2/s, 1088 MJ/kg, 2.76 mg/g, 15.28, 2.55 and 9.26, respectively. The results showed that drying under lower temperature and medium vacuum pressure increased the desirability index. The flow-ability of edible button mushroom powder was reported to be good.
Conclusion According to the results of drying tests of edible mushrooms, the following results of this study are obtained in infrared vacuum drying: 1- The effect of air temperature on all variables of button mushroom response was significant in vacuum-infrared dryer. 2- The air inlet temperature to the dryer had a negative effect on the specific energy consumption of the drying process and the total phenol content of the button mushroom powder. 3- Increase in air temperature caused a greater difference between the color indices of L*, a* and b* button mushroom powder than fresh mushrooms. 4. The results showed that drying under mild conditions (lower temperature and medium vacuum pressure) increased the desirability index. 5-Flow-ability of edible button mushroom powder was reported to be good.