Water relations of drumstick tree seed (Moringa oleifera): imbibition, desiccation, and sorption isotherms

Interest in seed propagation of drumstick tree (Moringa oleifera) has created a need for information about the water relationships of its seeds. Thus, we studied the imbibition and desiccation kinetics and adsorption/ desorption isotherms of drumstick tree seeds. Seeds absorbed water readily when imbibed at 23oC. After 17 h of exposure to an atmosphere of 100% relative humidity (RH), seed moisture content increased from 10 to 150% on a dry weight basis (dwb). Seeds lost water rapidly in a 1% RH still-air environment, and returned to their original seed moisture content in 24 h, indicating seed covering tissues are highly permeable to water. Adsorption and desorption equilibrium moisture content curves at 25oC were determined using the dynamic gravimetric method. Drumstick tree seeds equilibrated at relatively low moisture contents over all humidities, remaining below 10% (dwb) at RH levels below 80%. Five equations that are used to model seed moisture content as a function of RH were fit to the data using a non-linear regression method (modified Henderson, modified Chung-Pfost, modified Guggenheim-Anderson-de Boer, modified Halsey, and D’Arcy-Watt). The D’Arcy-Watt model resulted in the best fit for predicting the seed moisture content of drumstick tree seeds. In humid environments, drying seeds before long-term storage may increase the longevity of stored drumstick tree seeds.