FORMATION OF PORES IN FOODS DURING DRYING AND FRYING : A THEORETICAL MODEL

Characteristics of pores in food are one of the key structural parameters in many food products. Pores occur in diverse food products, such as cakes, breads and biscuits, breakfast cereals, extruded, fried and dried products and the issues of pores in foods are generic. The process of pore formation or collapse during drying is very complex in nature, and it is a challenge to the food engineers and scientists to predict characteristics of pores. A theoretical model (ideal condition) to predict the porosity in foods during drying is developed based on conservation of mass and volume principle, and assuming that volume of pores formed is equal to the volume of water removed during drying. As expected the ideal model may not be valid in many practical cases. The ideal model is then extended for non-ideal conditions, when there is either shrinkage, collapse or expansion, by defining a shrinkage-expansion coefficient. Experimental porosity data from the literature was used to estimate the shrinkage-expansion coefficient for selected food materials.