Characterization of deep-fat frying in a wheat flour-water mixture model using a state diagram.

BACKGROUND Crispness is an important characteristic to be controlled in deep-fat fried products. The physical state of food polymers influences the development of cellular structure and textural qualities of fried food. Glassy state is believed to play an important role in the mechanical properties of low-moisture food. Therefore, an understanding of the physicochemical phenomena in the development of fried food structure using a state diagram of the frying process is discussed. RESULTS Wheat flour models containing 400 and 600 g kg(-1) initial moisture content were fried in frying oil at 150 °C for 1-7 min. Thermal properties of wheat flour, structure alteration and textural properties of fried samples were evaluated. The porous structure continuously enlarged when the sample was in the rubbery state. As the frying time was prolonged, the state of the product became glassy due to a decrease in water content, resulting in the ceasing of porous enlargement. CONCLUSION The results revealed that physicochemical changes during frying influence the alteration of microstructure and quality of fried food, and the state diagram could be applied to explain the formation of microstructure during the frying process and used as a decision-making tool to choose the proper conditions to provide desirable qualities in fried food. Copyright © 2007 Society of Chemical Industry.