Record Detail

This study aimed to understand the micromechanism
of thermosonic pretreatment and microwave vacuum drying on
Agaricus bisporus. The water state and glass transition temperature
(Tg) of fresh and thermosonically treated Agaricus bisporus
slices during microwave vacuum drying were studied using differential
scanning calorimetry (DSC), low-field nuclear magnetic
resonance (LF-NMR), and magnetic resonance imaging (MRI).
Results showed that four population groups were contained in
the initial distribution of transverse relaxation time (T2) data of
fresh A. bisporus slices: T21 (0.38–7.05 ms), T22 (9.33–
32.75 ms), T231 (37.65–265.61 ms), and T232 (305.39–
811.13 ms). Thermosonic pretreatment significantly decreased
the initial free water content of A. bisporus sample but was accompanied
by a sharp increase in its immobilized water. BSemibound
water transfer^ appeared during microwave vacuum drying
(MVD) at moisture contents (Xw) of 0.70 and 0.60 g/g (wet
basis (w.b.)) for untreated and thermosonically treated samples,
respectively. MVD caused dramatic changes in the water state
and enhanced the Tg by decreasing the content and mobility of
immobilized water in A. bisporus tissues. The mobility of semibound
water for thermosonically and MVD-treated samples was
higher than for MVD-untreated samples, resulting in Tg values
decreasing by approximately 2–11.5 °C, but the uniformity of
water distribution in thermosonic-treated and MVD-treated samples
was better at Xw ≤ 0.52 g/g (w.b.).