Optimization of variable-temperature drying of Camellia oleifera seeds

Abstract

The processing method of Camellia oleifera fruit used in the industry was investigated, that is, fresh C. oleifera fruit was shelled in the drying equipment first and then the remaining C. oleifera seeds returned until the target moisture content (about 10% d.b.) was reached. The variable-temperature drying of C. oleifera seeds was investigated for the first time and the drying process was optimized and compared with constant-temperature drying. Two independent variables, including hot air drying temperature and air velocity, were studied by central composite design. The responses were drying time and quality of Camellia oil, including acid value and peroxide value. Results showed that the optimal constant-temperature drying conditions were drying at a temperature of 60.5°C and air velocity of 2.1 m/s. Under this condition, the total drying time was 607 min, and the acid and peroxide values were 1.72 mg/g and 0.12 g/100 g, respectively. The optimal variable-temperature drying conditions were drying at a constant air velocity of 2 m/s and a drying temperature of 55°C for 67 min, then 60°C for 213 min, and finally 65°C for 297 min. Under these conditions, the acid value was 1.75 mg/g and the peroxide value was 0.1 g/100 g. The optimal variable-temperature drying efficiency was 16.7% higher than that of constant-temperature drying when the optimization objective of drying time, acid value and peroxide value was 2:1:1.