The effect of process parameters and microstructural changes on a new convenience food – quick-frozen paste-coated mushrooms (Agaricus bisporus)

The technology of quick-freezing paste-coated mushrooms ( Agaricus bisporus ) was studied and optimized. The best microwave pretreatment condition for 1 cm slices, regarding color protection, was 5.4 W/g, for 55, 55–60 and 60 s for mushrooms with 3, 4 and 5 cm diameter caps respectively. For a batch of paste (668.2–1034.6 g), the process parameters considered were oil content (46.6–63.4 g), water content (381–562.6 g) and flour content (166–334 g) with a constant additional content of 30 g starch, 9 g baking powder, 2.6 g carrageenan, 30 g salt and 3 g pepper. These parameters were investigated using response surface methodology (RSM) with a central composite design. The optimal levels of the major paste components were 300 g flour, 432.5 g water and 50 g oil. The freezing time and sensory acceptability for paste-coated Agaricus bisporus (PCAB) under the optimized conditions were 7.49 min and 6.2 respectively. The freezing curves of PCAB were established at different temperatures and the freezing rates were calculated to find the freezing characteristics. In addition, the cell structure of PCAB, frozen at −75 °C, the lowest freezing temperature, and studied using transmission electron microscopy, was similar in quality to that of fresh Agaricus bisporus. The results suggested that Agaricus bisporus can be quick-frozen with a paste coating to produce an acceptable and nutritious convenience food.