Abstract
The purpose of this study was to clarify the effect of surfactant-added oils on the glass transition as a function of water content, fracture behavior, color, and crude oil content of the fried coatings (post-fried wheat flour-water mixture) obtained under various frying conditions (at 150-180 °C for 1.0-4.5 min). Polyglycerol oleic acid esters having hydrophile-lipophile balances of 7.4 (hydrophobic) and 13.3 (hydrophilic) were employed, and canola oils with and without 0.5 % (w/w) surfactants were used for frying. The samples obtained at 170 °C became glassy after frying times of 1.4 min, 1.9 min, and 2.4 min in the hydrophilic surfactant-added oil, hydrophobic surfactant-added oil, and surfactant-free oil, respectively. The glassy samples showed brittle fracture behavior, and the maximum fracture force for the glassy samples obtained using the surfactant-added oils was lower than that obtained using surfactant-free oil. The frying time to obtain glassy samples decreased with increasing frying temperature, and the frying time in the hydrophilic surfactant-added oil was reduced by 60-80 % compared to the surfactant-free oil. When the browning color of the glassy samples obtained for the shortest frying time was compared at each temperature, the samples fried in the hydrophilic surfactant-added oil showed less browning than those fried in the surfactant-free oil due to the reduction of frying time. There were no significant differences in the crude oil content between surfactant-free oil (69.9-105.7 g/100 g-defatted DM, dry matter) and the hydrophilic surfactant-added oil (78.6-115.5 g/100 g-defatted DM) at each frying temperature (except for 150 °C).