Microwave intermittent drying characteristics of camellia oleifera seeds

Abstract

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.

Effect of intermittent microwave drying on nutritional quality and drying characteristics of persimmon slices

“…Figure 2 presents the three stages of the drying process of persimmon slices under different microwave powers; acceleration, constant speed, and deceleration. Similar results were reported in the study of IMD of camellia oleifera seeds and ginkgo fruits (Zhang et al, 2013;Huang et al, 2021). Microwave power has a great influence on the drying rate of persimmon slices.…”

“…First, the dry basis moisture rate in the drying process of Gongcheng persimmon slices was calculated according to Equation 1 (Huang et al, 2021):…”

“…Microwave heating is an emerging technology. Compared with traditional heating, it can save more energy than traditional heating, because microwave heating speed is faster (Huang et al, 2021;Martins et al, 2022a). This is because, in the process of microwave heating, the microwave interacts directly with the material.…”

Evaluating of Microwave Drying for Hawthorn Slice as Alternative to Convective Drying

“…Similar results have been observed in the microwave drying of sliced Trabzon persimmon [13], green peas [15] and mango ginger [20]. The electromagnetic intensity increased by the increase of microwave power and therefore more microwave energy was absorbed by samples, which resulted shorter drying time due to accelerated the moisture migration and evaporation rate [10]. Figure 2 presents the changes of drying rate versus drying time.…”

“…Although convectional drying has been used for a long time due to its simplicity and affordability, it presents a highenergy consumption due to long process, and also leads to loss of quality because of high temperature [8]. Therefore, microwave-drying method is recently being studied as alternative to convective drying method due to high drying velocity and better food quality [10][11][12][13][14]. Microwave drying is based on electromagnetic waves to heat the material volumetrically, which leads to remove moisture from the food due to rising of temperature during microwave drying by application of an electromagnetic field [15].…”