CONFOCAL LASER SCANNING MICROSCOPY IMAGING OF DEEP-FAT FRIED BATTER COATING

Porosity and pore size distribution are very important microstructural properties of fried foods needed in process optimization and product development. Confocal laser scanning microscopy provides a means of imaging food samples to qualify and quantify specific components identified by staining, and also produces images of higher resolution compared to the conventional light microscopy. The objectives of this study were to characterize pore properties and quantify fat distribution of deep-fat fried chicken nuggets batter coating using confocal laser scanning microscopy imaging. Chicken nuggets were fried at three temperatures namely 170, 180 and 190°C. Detached batter coatings were stained non-covalently with drops of 0.005% solution of Nile Blue A, cryosectioned to 60 µm and 2-D images were obtained at fluorescence and reflection modes of the microscope. The images were quantitatively analyzed for fat and pore characteristics. Fat distribution was significantly affected by frying temperature and time and it decreased within the depth of the coating's thickness. The correlation coefficients between fat distribution obtained from the image analysis and fat content obtained by the conventional method ranged between 0.60 - 0.79 and the relationship was only significant (P<0.05) at two temperatures, 180 and 190°C. Porosity ranged from 4.97 to 32.7% and was significantly influenced by frying temperature. Pore size varied between 1.2 and 523 µm. There was formation of small and big pores with frying time. The results show that fat distribution and pore properties of fried chicken nuggets batter coatings are influenced by the frying conditions, and that fat content can be predicted from fat distribution data at elevated frying temperatures.