Microstructural changes during frying of foods

Food products undergo several chemical, nutritional and physical changes during deep-fat frying. Starch components are gelatinized, proteins are denatured, some nutrients are destroyed, various avor components are developed, crusts are formed and pores are developed to form unique microstructures during the frying process (Moreira and Barrufet 1996). These changes combine to give fried foods their unique textural and sensory characteristics which have been dif cult to replicate using anyother unit operation. Frying is a simultaneous heat and mass transfer process. Oil acts as the heating medium and facilitates mass transfer. Heating occurs from the surface into the interior of the food material by convection and conduction modes of heat transfer. The overall product temperature is increased, leading to formation of water vapor which burrows its way to the surface of the product due to a pressure and concentration gradient, leaving behind pores that become signi cant in subsequent oil absorption. Heat also causes caramelization of sugars and induces reactions between amino acids and reducing sugars, creating the brown or golden coloration and hardness of the crust that are characteristics of some fried foods. Further, there are signicant changes in the volume of the nal product due to shrinkage at the elevated temperatures during frying.