Experimental study on transport mechanisms during deep fat frying of chicken nuggets

Two important factors affecting oil uptake of food products during deep fat frying (DFF) are water content and pressure development. This study tries to explain the complex mass transfer mechanisms taking place during DFF with respect to real time pressure variations inside chicken nuggets. Breaded chicken nuggets were made with and without 5 g/100 g methylcellulose (MC) added to predust. Frying experiments were performed at 175 °C and 190 °C for 0, 30, 60, 120 and 240 s. The gage pressure increased rapidly after the nuggets were introduced into hot oil. As frying progressed the pressure inside the nugget decreased to negative values (suction). During post frying cooling there was a further reduction in pressure. The MC-coated nuggets had lower fat uptake and moisture loss than control nuggets for both frying temperatures. Scanning electronic microscopic analysis showed that the control nuggets had greater randomness in the crust, core and meat layers in terms of microstructure development, surface texture, rigidity and pore sizes than MC-coated nuggets. Higher frying temperature resulted in increased complexity of microstructure. The nuggets fried in dyed oil showed oil penetration up to 1-4 mm into the meat layer. This implied that the oil uptake was a surface phenomenon.