Characterization of Food Product Surfaces during Drying Using Fractal Geometry

Introduction ........................................................................................................ 483

Materials and Methods ..................................................................................... 484

Results and Discussion ..................................................................................... 486

Descriptive Model for Drying of Agar-Maltodextrin Slabs ...................... 490

References ........................................................................................................... 492

During drying, moisture and temperature profiles as well as morphology of

materials follow a nonlinear behavior. Variability of drying conditions and

heterogeneity of materials contribute to this phenomenon. It is also known

that microstructure of the material influences diffusion (Gekas and Lamberg,

1991; Cronin and Kearney, 1998; Aguilera and Stanley, 1999). Tensions within

structural networks and formation of crusts of different permeability to

water transport cause fractures associated to drying. The presence of

tensions in the structural networks of materials and the formation of

partially impermeable crusts on the exterior layers may cause fractures

associated to shrinkage and the presence of tension forces within thematerial

(Brinker and Sherer, 1990). An alternative to describe the complexity of

drying may be the use of the fractal theory (Doulia et al., 2000). Some authors

have proposed equations to describe molecular and convective transport

through fractal structures, and have also applied them to chemical kinetics

and media transport in more than two phases (Giona et al., 1996a, 1996b).

However, analysis of the surfaces of biological products and the application

of fractal geometry may provide useful information to find relationships

with processing variables. Fractal geometry leads a numeric description of

structural changes that biological products undergo when processed. In the

drying operation it may be interesting to correlate transport parameters as

well as operating conditions with fractal dimension of the material, and this

is the main objective of the present work.