Effects of porous structure and water plasticization on the mechanical glass transition temperature and textural properties of freeze-dried trehalose solid and cookie

This study aimed to examine the effects of porous structure and water plasticization on the mechanical glass transition temperature (Tg) of freeze-dried trehalose solid and cookie. The thermal Tg and mechanical Tg were evaluated by differential scanning calorimetry (DSC) and thermal rheological analysis (TRA), respectively. The mechanical Tg of the porous trehalose sample was slightly higher than that of the pellet sample. The mechanical Tgs for pellet and porous trehalose samples were higher than thermal Tg. Although pellet, crust, and crumb cookie samples showed indistinct glass transition behavior in the DSC thermosgrams, TRA revealed a clear glass transition. There were little differences in the mechanical Tg of the cookie samples. The mechanical Tg decreased with an increase in water content, and mechanically and thermally critical water contents (water content at Tg = 25 °C) were evaluated. Fracture properties of the cookie sample changed discontinuously at the thermally critical water content.