The fact that the surface temperature
is higher than the surrounding air only implies that the heat of
respiration is heating the product. This is in agreement with Song
et al. (2002) who proposed a mathematical model based on heat
and mass transfer balances accounting for the respiratory and
transpiratory behaviour of fresh produce, and the transport
phenomenon across the package. When the ambient air is below
saturation level, the difference in water vapour pressure between
the product surface and the ambient air will cause moisture
evaporation from the product surface resulting evaporative
cooling. In this case, the produce surface temperature is lower
than the air temperature. This was evident from the measured
surface temperature of mushroom (10.8 C) which was below the
surrounding air temperature and the mushroom showed a rapid
decrease in mass due to transpiration (Fig 4).