Optimization of Freeze-Drying Process Parameters for Qualitative Evaluation of Button Mushroom(Agaricus bisporus)Using Response Surface Methodology

Button mushroom cubes of constant cross-sectional area (0.75 cm × 1.5 cm) and varying thickness (2 mm, 5 mm, and 8 mm) were freeze-dried. Pressure (0.04, 0.07, and 0.10 mbar), primary drying temperature (−2°C, −5°C, and −8°C), and secondary drying temperature (25°C, 28°C, and 31°C) were taken as drying parameters. The protein, ascorbic acid, and antioxidant contents were taken as quality estimates for freeze-dried mushrooms. It was observed that the secondary drying temperature affected the protein ( p<0.05 ) and antioxidant content ( p<0.01 ) significantly, whereas all three freeze-drying parameters affected the ascorbic acid content with higher effect due to temperature parameters ( p<0.01 ) as compared to pressure ( p<0.05 ). The optimized values for protein, ascorbic acid, and antioxidant content obtained using response surface methodology were 7.28±0.56 mg/g, 26.92±0.87 mg/100 g, and 8.60±0.44 mg/g, respectively, as compared to 8.43±0.21 mg/g, 28.00±0.53 mg/100 g, and 9.10±0.10 mg/g, respectively, for fresh button mushrooms. The optimum values for process variables were obtained as 0.09 mbar, 0.36 cm, and −7.53°C and 25.03°C for pressure, sample thickness, and primary and secondary drying temperatures, respectively.