Universal or species-specific influence of moisture on the glass transition in various horticultural seeds?

Preferably plant seeds are stored in the glassy state to slow deterioration reactions. Thus, it is valuable to know at which moisture content (MC) seeds reach the glassy state and if this is universal or species-specific. We investigated the glass transition temperature (Tg) of seeds using several methods. Dynamic mechanical analysis of intact seeds with a 3 °C/min heating rate was the most suited analysis method for brassica seeds. This method was applied to seeds from four Brassica oleracea (brassica), two Lactuca sativa (lettuce) varieties and one Daucus carota (carrot) variety, equilibrated to several MCs. As oil does not mix with water, it will not contribute to the glass transition. Hence, MC should be based on the dry matter only present in the hydrophilic phase, thus excluding oil, to more accurately describe the Tg curve. This results in significant differences for different species based on MC excluding the oil content, which is a novel approach. Lettuce has a higher oil content and thus a significantly higher Tg curve than brassica. However, the curves are rather similar when based on MC including oil, as observed in previous studies. Thus, a universal Tg curve can be advised as a rule of thumb if no other information is available. For precise drying and storage optimisation, the species-specific Tg curve can be used.