Revealing moisture migration characteristics of Camellia Oleifera shell in hot air drying through steam partial pressure, moisture binding energy, shrinkage

The moisture migration characteristics of Camellia oleifera shell (COS) have a critical role in the shell explosion of Camellia oleifera fruit under hot air drying. To reveal the moisture migration characteristics of COS, a drying setup was constructed. Additionally, an equilibrium moisture content equation for COS was provided. Also, the evolving patterns of equilibrium moisture content, shrinkage, shell explosion rate, and moisture migration parameters were explored. Results indicated that the coefficients A, B, and n of the equilibrium moisture content equation fitted by the modified Henderson model were 6.424 × 10^–4, 38.8, and 1.213, respectively. The surface steam partial pressure of COS initially increased and then decreased with increasing drying time. The moisture binding energy was close to zero when the moisture content was greater than or equal to 70% (d.b), and moisture content of 70% (d.b) was adopted as the reference point for adjusting the drying process parameters. The shrinkage rate of COS dried to the moisture content of 15% (d.b) ranged from 43.1% ~ 65.3% within the temperature of 45–85 °C. The shell explosion rate at the temperature of 50 °C was only 8.3% of that at the temperature of 70 °C, the starting time of shell explosion of Camellia oleifera fruit at the temperature of 70 °C was 44% earlier than that at the temperature of 50 °C.