Texture of Glassy Tapioca-Flour—Based Baked Products as a Function of Moisture Content

摘要

Texture change of tapioca-flour–based baked products as impacted by moisture content (MC) was investigated along with the products' glass transition. The baked products were initially in a glassy state with water activity (a_w), MC, and midpoint glass transition temperature (T_(g,m),) of 0.38, 3.9% and 148°C, respectively. While a_w remained lower than 0.54 (6% MC), the products' crispness was satisfactorily preserved (score > 5). A mechanical test showed a concave dependence of the products' hardness and work (area under the hardness peak) with increasing MC. When the products' hardness or work reached a maximum and began to reduce, at a_w 0.54 (MC 6% and T_(g,m) = 132.8°C), the products' texture became slightly soft (score = 5, unacceptable texture). This suggests that maximum hardness and work could be used to identify critical a_w which results in an unacceptable loss of crispness. The sorption isotherm indicates the amount of water in the monolayer was –2.5% MC (a_w~0.1). This amount of water was much lower than that at the critical a_w for acceptable crispness. A plasticizing effect of water on the products' glass transition in the a_w range of 0-0.86 resulted in a decrease in T_(g,m) from 173.7 to –10.1°C. Such texture deterioration occurred even though the products were still in a glassy state.