The migration of frying oil into the chicken nuggets was observed by frying the nuggets in oil dyed with lipid soluble, heat
stable and water insoluble Sudan red dye. The migration of oil and Sudan Red were similar into the food. So, it can be used as a marker that is identical to localized oil in fried foods (Keller et al.,1986). The nuggets were fried in oil for 0.5,1, 2, 4 and 8 min durations at 175 C and 190 C temperatures. The Fig. 15 shows the localization of the dyed oil in the control and MC chicken nuggets. The primary aim of these experiments was to determine, whether the oil uptake was a surface phenomenon. The observation of the figure shows that the oil deposition in the chicken nuggets was mainly around the crust region, and interface between the crust and core. The oil did not reach up to the center of the nuggets. The dyed oil content in the outermost layer of core corresponds to greater average fat uptake in crust and lower fat uptake into the core region of the nuggets as mentioned in the fat analysis section. The oil penetrated up to a depth of 2 mm in all the treatments. Slightly higher oil penetration was observed in control nuggets when compared to the MC nuggets. This might be due to higher magnitude of negative pressure in the control nuggets. Similar observation on oil penetration limiting to the crust less than 1 mm depth was made for French fries by Farkas and Singh (1991) and Keller et al. (1986). The moisture loss, and dye penetration into the nuggets increased with the increase in frying temperature, and time. The thin layer of crust appeared to act as a barrier to mass transfer during DFF. Thus, the oil was mostly localized around the corners and edges of the crust and broken slots (Pinthus & Saguy, 1994). Most of the cooking oil will be located in the outer two layers of the food (Aguilera & Gloria, 1997). The results from various frying experiments for DFF potato products showed that the location of the oil was mainly on the crust as well as in the regions around the middle layer of cells just beneath the crust, and the core was virtually oil free.