True thermal conductivity determination of moist porous food materials at elevated temperatures

Thermal conductivity (k) of bread samples, moisture content 5% to 44%, (w/w , wet basis) and porosity 0.18 to 0.90, was measured in a sealed stainless steel vessel using the probe method from 25 to 85 degrees C. Significant di fferences were observed in measured thermal conductivity before and after a ir pressure was applied to the sample indicating the influence of vapor pha se moisture migration on thermal conductivity,The difference increased as t emperature and moisture content were increased. True thermal conductivity o f bread was found to agree with predictions using a volume fraction model w hen moisture migration was completely suppressed at an applied air pressure of 18 atm.