Water sorption isotherms of vegetable seeds as influenced by seed species and storage temperature

Abstract

The water sorption isotherms of seeds of four vegetable species; carrot, cucumber, onion, and tomato were determined using the static method of eight saturated salt solutions (relative humidity range from 11 to 98%) at four storage temperatures; 5, 15, 25, and 35°C. The water sorption isotherms of each crop exhibited a reverse sigmoid shape. When seeds were stored at low relative humidity (RH), their equilibrium moisture contents (EMC) were relatively low. At 5°C, no major changes in moisture sorption up to 80% RH. Beyond this point, a sharp increase in EMC occurred. In general, no major differences in water sorption isotherms were observed between species at low relative humidities. Differences became obvious when seeds were stored at RH higher than 60% except for seeds held at 5°C and 15°C. In general, the increase in storage temperature increased the water activity (aw) of seeds. At 97% RH, seeds held at 25 and 35 °C deteriorated before reaching equilibrium. The experimental data were fitted well with GAB and Henderson equations. Equilibrium moisture content varied from a minimum of 0.00236 (g water/g dry matter) for tomato to a maximum of 0.0388 for carrot. The correlation coefficients (0.968 to 0.999 for GAB model and 0.922 to 0.961 for Henderson model) indicated a good fit to experimental data. The GAB model fits experimental data better than Henderson model as indicated by the higher correlation coefficient values.