Thermal characteristics of Agaricus bisporus mushroom: freezing point, glass transition, and maximal-freeze-concentration condition

The stability of foods strongly depends on the state of water (i.e. water activity) and temperature. Agaricus bisporus mushroom plays an important role as a nutritional and functional food; however little information is available on the effect of processing on its stability. This study measures the thermal characteristics and sorption isotherm of Agaricus bisporus by differential scanning calorimetry (DSC) and isopiestic method, respectively. Thermograms of samples containing un-freezable water (below moisture content 0. 11 g/g sample, i.e. wet basis) showed no glass transition which is indicative of the complexity of mushroom texture. Samples containing freezable water above 0.17 g/g sample exhibited glass transition. The BET monolayer value was 0.061 g/g dry-solids (i.e. dry basis). Actual maximal-freeze-concentration conditions was found as Xs’ (characteristic solids content) = 0.782 g/g sample, and Tm’ (characteristic end point of freezing) = -30°C. The glass transition data and isotherm of A. bisporus containing un-freezable water could be used to determine stability region of dried mushroom during its storage, whereas Tm’ to determine the stability for the frozen storage. In addition it could be used in designing drying and freezing processes, respectively.