Moisture sorption isotherms of four vegetable seeds as influenced by storage conditions

The moisture sorption isotherms (MSI) of beet, cabbage, lettuce, and okra seeds were determined using the static method of nine saturated salt solutions (relative humidity range from 13.2 to 96.5%) at four storage temperatures (5, 15, 25 and 35degreesC). The MSI for each crop exhibited a reverse sigmoid shape. In general, there were variations of sorption isotherms among crops. It was observed that, at a given moisture content, water activity (a(w)) was higher for cabbage, followed by lettuce and beet and then okra. The differences became noticeable when seeds were stored at relative humidity higher than 60%. This suggests that cabbage seed is the most susceptible to deterioration and okra seed is expected to have higher longevity. As anticipated, temperature increased a(w) at a given equilibrium moisture content (EMC)t. At 35degreesC, a(w) was higher at any given EMC and at 5degreesC little changes occurred in moisture sorption up to 80% ERH. Beyond this point, a sharp increase in EMC occurred. At 97% ERH, seeds held at 35degreesC deteriorated before reaching equilibrium. The experimental data fitted well GAB and Henderson models. The correlation coefficients were 0.882 to 0.996 for GAB model and 0.964 to 0.994 for Henderson model, respectively.