Moisture sorption and thermodynamic properties of Camellia oleifera seeds as influenced by oil content

Abstract

Moisture sorption isotherms and thermodynamic properties of Camellia oleifera seeds as influenced by oil content were investigated. Moisture desorption and adsorption isotherms of Camellia oleifera seeds, kernels and shells from three varieties were determined using constant temperature and humidity chamber method at different temperatures (10°C, 25°C, and 40°C) with water activity ranging from 0.20 to 0.90. Six selected mathematic models were employed to fit the experimental data. The Peleg model gave the best results for both seeds and kernels and Langmuir model was the best for shells. The difference of equilibrium moisture contents at the same water activities during desorption and adsorption indicated the occurrence of hysteresis of adsorption processes and the equilibrium moisture contents tended to decrease with the increasing oil content and temperature. The binding energy and average capacity per unit mass decreased with increasing temperature and oil content. The relationships between water activity and the logarithm of sorption activity showed the capillary porous body characteristics of the seeds.

Seed Moisture Isotherms, Sorption Models, and Longevity

“…In terms of composition, for heterogeneous materials such as seeds, the amount of oil they contain largely determines how much water will be adsorbed, as reflected in Cromarty's equation which includes oil content as a variable (Cromarty et al, 1982 ; see below and Figure 4D ). The lower the oil content, the greater the amount of water that will be adsorbed, as seen for example for seeds of Camellia oleifera with differing oil content (Zhu et al, 2021 ). This is a key reason why equilibrating seeds so they have the same eRH can be considered preferable to equilibrating seeds to the same moisture content when comparing physiological responses such as seed longevity across diverse species (Hay et al, 2022 ).…”

“…Temperature also modifies the shape of the isotherm. As temperature is reduced, for seeds with a given eRH, the moisture content is higher; or conversely, as temperature is reduced, at a given moisture content, the eRH is lower (Vertucci and Roos, 1993 ; Fang et al, 1998 ; Kartika et al, 2012 ; Zeymer et al, 2017 ; Arslan-Tontul, 2020 ; Zhu et al, 2021 ) ( Supplementary Figure 1 ). Again, this effect tends to be greater over the mid-eRH-range, as seen for example, for seeds of grape (Maleki Majd et al, 2013 ), rice (Mousa et al, 2014 ) and maize (Talla, 2014 ), though this pattern was less apparent in the isotherms determined for seeds of pea, soya bean and peanut by Vertucci and Roos ( 1993 ).…”