Effects of Trehalose Content and Water Activity on the Fracture Properties of Deep-fried Wheat Flour Particles and Freeze-dried Porous Waxy Corn Starch Solids.

Wheat flour-based batter containing 0 to 20 % trehalose was deep-fried, dried and held in various water activity ( ) conditions. The effects of trehalose content and on oil content, water sorption, isothermal mechanical relaxation, and fracture properties were investigated. For comparison, the fracture properties of freeze-dried porous waxy corn starch solids were also investigated. The 10 % trehalose sample had the lowest oil content, water content, and . A force-reduction value (∆) of the samples was evaluated as a typical mechanical relaxation parameter. ∆ gradually increased with increasing and sharply increased above a specific presumed to be associated with the glass to rubber transition. Compared to ∆ values among the glassy samples, 10 and 20 % trehalose samples had higher ∆ values (were more rigid) than 0 and 5 % trehalose samples. From the fracture measurements of the glassy samples, the first fracture force increased linearly and the number of fracture peaks decreased linearly with increasing . At each , 10 % trehalose had the lowest first fracture force and the highest the number of fracture peaks. Freeze-dried porous waxy corn starch solids showed similar fracture properties to deep-fried samples. These findings suggest that around 10 % trehalose content is optimal for producing deep-fried foods with a brittle texture.