Introduction: Considering the serious challenges related to the waste of agricultural products and the limitations in the traditional storage and processing methods, the use of new technologies such as drying and tablet production seems necessary. Mushrooms also have antifungal, anti-inflammatory, anti-cancer, antiviral and antibacterial effects. After harvesting, mushrooms have a shorter shelf life than other vegetables due to their high humidity, high respiration rate, lack of cuticle and intense enzymatic activity. They spoil quickly and begin to change color immediately after harvesting. In order to increase their shelf life, edible mushrooms must undergo processing processes, so researchers have investigated various methods for preserving and increasing the shelf life of mushrooms. However, drying is one of the most common methods used for edible mushrooms. Therefore, this research was done with the aim of optimizing the drying and tableting processes for a valuable and perishable product such as edible button mushrooms.

Materials and Methods: Edible button mushrooms were purchased from the local market and after cleaning and washing, they were cut into pieces with a thickness of three millimeters. Then, the samples were placed in the oven for 24 hours to obtain its initial moisture, and finally they were dried by two methods of drying in the shade and drying with a continuous dryer. Then the dried mushrooms were powdered and shaped into smooth round tablets. For this purpose, the tests were defined in the form of a central composite design in Design Expert software version 13. Independent variables (input) to Design Expert software in continuous dryer including temperature (50, 60 and 70 degrees Celsius) and air speed (1.5, 2.5 and 3.5 m/s) and dependent variables for drying included total phenol, antioxidant property and color parameters. Regarding the optimization of the tableting process, independent variables include: pressure (50×105, 60×105, 70×105, 80×105 and 90×105 Pa), stress relaxation time (3, 8, 13, 18 and 22 s) and mold diameter (10, 14, 18, 22 and 26 mm) and the dependent variables included penetration resistance, stress along the diameter and density.

Results and Discussion: According to the findings, the air temperature variable had a greater effect on the response variables than the air velocity variable. According to the results obtained from the optimization, the conditions in which the air temperature was 64.1°C and the air velocity was 2.49 m/s were selected as the optimal conditions with a desirability of 76.3%. The edible button mushroom sample dried in optimal conditions has a total phenol content of 10.7 mg of gallic acid in the weight of the dry sample, antioxidant property of 91.72%, brightness index (L*) 69.73, redness index (a*) was -23.44 and the jaundice index (b*) was 1.80. The shade-dried sample also has a total phenol content of 2.87 mg of gallic acid in the weight of the dry sample, antioxidant property of 91.27%, brightness index (L*) of 72.54, redness index (a*) of 09 -9/ and the yellowness index (b*) was 6.74. According to the total phenol content and antioxidant property in the continuous drying method, this method was more favorable than the shade drying method. Among the factors affecting the mechanical properties of tablets prepared from dried mushroom powder by the continuous method and shade, the die diameter variable was more effective than the other two variables. To optimize the tablet obtained from dried mushroom powder by continuous method, the conditions in which the pressure was equal to 72.74 ×105 Pa, the die diameter was 14 mm, and the stress relaxation time was 8 seconds, with the desirability of 71.8% as a point. Optimum was selected. For shadow-dried mushroom powder tablets, the conditions in which the pressure was equal to 80×105 Pa, the diameter of the mold was 18.70 mm, and the stress relaxation time was 18 seconds were selected as the optimal point with a desirability of 60.1%.

Conclusion: From the comparison of the optimal conditions obtained from the optimization for the two powders dried by the shade and continuous methods, it can be stated that the optimal tablet sample obtained from mushroom powder dried by the continuous method was more desirable than the optimal tablet obtained from mushroom powder dried in the shade.
In general, it can be concluded that drying by continuous method can be a good option to replace drying by traditional method. Because the tablet obtained from mushroom powder dried by the continuous method had a higher density, penetration resistance and stress along the diameter compared to the shadow method.