Thermo-physical properties of wheat germ: Heat and mass transfer during convective heating

Abstract

Wheat germ is one of the most nutritious parts of the grain. It is not fully exploited because it is highly perishable. Many attempts were done in order to stabilize the germ, being the most traditional one convective heating. The aim of the present work is the determination of thermo-physical properties of wheat germ by using a specific methodology considering temperature and moisture content variations. A single-phase mathematical model was used to validate the properties of wheat germ. The particulate material was considered from a continuum approach. Coupled heat and mass transfer equations were solved using a finite element method. The model was validated against experimental trials at three different oven temperatures (150°C, 180°C, and 200°C). A good accuracy was achieved considering the complexity of the material and processes involved. Water activity and lipase activity (two very important stability parameters) of the heated samples were predicted from average moisture content and temperature. Practical Applications: Wheat germ is a highly available by-product. Stabilization procedures are mandatory in order to use it in food formulation. Properties like density, specific heat capacity, and thermal conductivity of the particle and bulk, as well as effective moisture diffusivity, heat, and mass transfer coefficients might be useful when describing similar thermal stabilization procedures of wheat germ or other particulate materials. Changes of these properties during thermal treatment involving a wide range of temperature (25–100°C) and moisture content (0%–13%) are also useful in designing, optimization, or scaling-up processes.