Quantification of Changes in Relative Humidity and Seed Moisture Contents of Canola Cultivars under Different Temperatures Using Hygroscopic Equilibrium Curve

Introduction : Seeds, like other materials, are hygroscopic and exchange moisture with their surroundings. The changes in the moisture of seeds during storage depend on their hygroscopic nature and this feature plays an important role in determining the seed quality and longevity. Furthermore, studying the hygroscopic characteristics if seeds can be useful in seed storage studies as well as in commercial applications such as drying and seeds processing. Therefore, in this study, the relationship between seed moisture content and relative humidity in seed of rapeseed cultivars was studied. Material and Methods: In this study, the relationship between the ambient relative humidity and seed moisture content of three rapeseed cultivars at 10, 20 and 30 °C was investigated using hygroscopic equilibrium curves. Therefore, water desorption and absorption curves were studied separately. Water absorption and desorption curves were obtained by drying the seeds at 1% relative humidity and seed hydration at 100% relative humidity, respectively, followed by transferring the seeds to different relative humidities at different temperatures and finally determining the equilibrium moisture content of the seeds. It should be noted that glycerol and sulfuric acid solutions were used to creation different relative humidity. Finally, the relationship between seeds moisture content against the relative humidity was quantified by fitting the D’Arcy-Watt equation. Results: The results indicated that the seeds moisture content varied in cultivars and temperatures at different relative humidities. Also, there was a difference between water desorption and absorption curves in all cultivars and temperatures; desorption curves were generally higher than water absorption curves. The greatest difference among the cultivars regarding seed moisture content was observed at 100% relative humidity, and this difference was less severe at lower relative humidities. Also, the highest seed moisture content of rapeseed cultivars was observed at 20 °C and 100% relative humidity, and the lowest seed moisture content was recorded at 30 °C and 1% relative humidity. Conclusions: According to the results, it was found that the relationship between seed moisture content and relative humidity followed a sigmoidal function, and this relationship would also vary depending on cultivar and temperature. There was also a difference between the adsorption and desorption curves, which is called "hysteresis", and showed that the seed moisture content at a constant relative humidity was generally higher in the state of dehydration compared with that in the state of hydration. Due to this event, desorption curve is situated higher than the absorption curve.