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This paper reports on an experimental investigation of the drying characteristics and kinetics of camellia oleifera seeds under microwave intermittent drying conditions. The effects of key parameters such as microwave power, heating time, and the length of the intermittent time are discussed in detail. The energy consumption in the drying process along with the main quality parameters of camellia oil, namely the peroxide and acid values, have also been determined and compared with hot‐air drying. Results show that the microwave drying curve consists of an acceleration rate period, a constant rate period and a falling rate period. As the microwave power and heating time increase, the drying time decreases. While as the length of the intermittent time increases, the drying time increases. The hot‐air drying time was found to be much longer than microwave drying time, and the energy consumed during hot‐air drying was also several hundred times higher than that used during microwave intermittent drying. The acid and peroxide values of camellia oil after hot‐air and microwave drying were both within the allowable range in the National Standard of China. The Midilli and Kucuk model was the best model to describe the kinetics of the drying process.Practical applicationsDrying is the first step in the processing of camellia oleifera seeds, which not only affects the storage of camellia oleifera seeds, but also affects the quality of camellia oil, and has thus become a research hotspot in recent years. However, several disadvantages of hot‐air drying have been identified like the slowness of the drying process and the relatively large energy consumption. Therefore, finding a drying method that is more suitable is necessary. Microwave intermittent drying is a type of discontinuous drying. The moisture and temperature inside the material can be evenly redistributed during the intermittent time, so that the material is not overheated. This feature of preserving the quality of the products to be dried has made microwave intermittent drying attractive and has been successfully applied to agricultural, forestry, and food products.

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The heat transfer characteristics and kinetics of Camellia oleifera seeds under hot-air drying were investigated at different temperatures (40, 60, and 80 °C) and loading densities (0.92, 1.22, and 1.52 g/cm2) with a constant air velocity of 1 m/s. Twelve common drying kinetic models were selected to fit the experimental data. The most suitable model was chosen to describe the hot-air drying process of C. oleifera seeds and help in its optimization. The results showed that the drying temperature has a significant influence on the hot-air drying characteristics of C. oleifera seeds. As the drying air temperature increases, the drying time decreases. The effect of the loading density on the drying characteristics of C. oleifera seeds is much smaller than that of temperature. With the increase in the loading density, the drying time slightly increases. The hot-air drying curve of C. oleifera seeds consists of a very short acceleration rate period at the beginning and a long falling rate period, indicating that the drying of C. oleifera seeds is mainly controlled by the diffusion of moisture inside the material. An effective moisture diffusion coefficient of C. oleifera seeds was estimated to range from 0.81256 × 10−9 to 3.28496 × 10−9 m2/s within the temperature range studied. The average activation energy was 28.27979 kJ/mol. The logarithmic model was found to be the best model to describe the kinetics of hot-air drying of C. oleifera seeds.

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Infrared drying characteristics and quality variations (color change, hardness, contents of polyphenol and flavonoid) of lily bulb under blanching pretreatment are investigated. Influences of parameters such as pretreatment temperature and time, and infrared drying temperature are discussed. Effective moisture diffusion coefficient, activation energy and energy consumption were calculated. The drying time was reduced by 62.5%, 56.3% and 61.5% at 90 C compared to 60 C when blanching time was 4, 5 and 6 min, respectively. A blanching time of 5 min and drying temperature of 70 C were ideal for pretreatment and drying to maintain good color quality. Hardness value of lily bulb decreased as drying temperature and blanching time increased. 70 - 80 C was ideal drying condition to maintain good hardness quality. Blanching time and drying temperature differently affected contents of flavonoids and polyphenols of lily bulb. Basically, when blanching time was relatively long and drying temperature was relatively high, the content of flavonoids and polyphenols was high. Traditional lily bulb drying methods, sun drying and fire drying, may cause browning, and hence nutritional value and appearance quality are deteriorated. Infrared drying has high drying efficiency and good preservation of nutrients, and blanching pretreatment can effectively alleviate the degree of browning. Thus infrared drying with blanching pretreatment is ideal for lily bulb drying, however, investigations are limited. This paper presents effects of pretreatment temperature, pretreatment time and infrared drying temperature on drying kinetics and quality variations to provide guidance for storage and processing of lily bulb.

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.