Thermodynamic Properties of Seeds: A Review

Study of isotherms and thermodynamic properties become essential to understand the drying and imbibition mechanisms of seeds. Among post-harvest procedures of seeds, drying is widely known and used in order to assure quality and stability during storage and shelf life. Variation of moisture content through drying is important in order to understand the interaction between water molecules and the seed components, which is the key factor for correct drying and storage. Seed viability could be maintained during long periods owing to their glass structure, as a thermodynamic unstable state, with high viscosity. Thermodynamic properties were enthalpy (Amount of energy available to do work), entropy (Amount of energy present but it not available to do work) and gibbs free energy (Differential energy between the enthalpy and entropy). Thermodynamic properties of seed water determines the reaction kinetics during seed deterioration. Thermodynamic properties showed a critical upper limit, with tolerant species having higher values then susceptible species. In general the values of critical limits of the thermodynamic parameters decreased with increasing temperature. The differential enthalpy and entropy increased in seeds with period of storage and became asymptotic as the seed lost their viability. Thermodynamics properties increased with increase in temperature, indicating that drying and water absorption do not occur spontaneously it requires external energy. A radical drop in germination follows the trend of gibbs free energy increase and enthalpy decrease, indicating intensification of endergonic reaction. Hence, it is concluded that by using thermodynamic properties of seeds the seed quality can be determined without conducting the germination test in shortest period.