Microstructural characterization of deep-fat fried breaded foods

Michael O. Ngadi, McGill University, Montreal
Akinbode A. Adedeji, McGill University, Montreal
Lamin Kassama, University of Wisconsin - Stout

Abstract

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 flavor components are developed, crusts are formed and pores are developed to form unique microstructures during the frying process (Moreira and Barrufet, 1996). All these changes combine to give fried foods their unique textural and sensory characteristics which have been difficult to replicate using any other 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 product’s surface due to pressure and concentration gradient, leaving behind pores that become significant 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 significant changes in the volume of the final product due to shrinkage at the elevated temperatures during frying. There have been substantial attempts to understand the changes that occur during deep-fat frying at the macro level. However, several of these changes occur at micro levels. Thus it is vital to examine microstructure evolution in fried products in order to develop techniques that would enhance their effective study and control. Techniques that are used in medical, biological and material sciences to study materials at the micron scale are recently being adapted to study foods (Aguilera, 2005). Microscopy techniques and X-ray imaging have been used to some degree. Advances in computer image analysis have also enhanced the digital and quantitative analysis of obtained image dataset. The contribution of these techniques in the study of microstructural changes during food processing such as frying is considerable. In this chapter, the focus is on reviewing the microstructural changes during deep-fat frying; present various modern approaches to studying food microstructures and illustrate how quality is affected by microstructural changes.