Rapeseed meal (RSM), mainly used as a protein-rich component of animal feed, is susceptible to quality degradation under the influence of high relative humidity and ambient air temperature. The aim of this study was to
present empirical data and water vapour sorption isotherms for rapeseed meal at various ambient air conditions.
The equilibrium moisture contents (EMCs) of RSM at two temperature levels (25 °C/40 °C), a wide range
of water activities (0.3‒0.9) and two sorption pathways (adsorption /desorption) were determined, using a static
gravimetric method. Mathematical equations were applied to analyse the experimental data, of which the modified GAB and modified Halsey were found to be the best fitting models, with correlation coefficients ranging
from 0.983 to 0.998. It was observed that the EMC of RSM decreased with increasing temperature, but this
effect was not statistically significant at water activities above 0.6. The hysteresis was statistically significant
in the region of water activities from 0.3 to 0.6, but the greatest differences between moisture bound by attachment and evaporation mechanisms were revealed at the lower values of this range. The area of the hysteresis
loop was smaller for the isotherms plotted at higher temperature. It was concluded that a moisture content up
to 10.5% would be appropriate for short-term handling of RSM during trading, whereas for long-term storage
at temperatures of 20 °C or below, a moisture content between 5.5% and 8.5% wet basis should be maintained.
The results presented in this study may be applicable to the design of technological and storage parameters,
necessary to ensure the microbiological and chemical stability of RSM during handling in international trade.