Radiofrequency (RF) treatment is a dielectric heating method (Cao et al., 2021; Jiao et al., 2017; Mao et al., 2021), using RF energy as a heating source in the drying process of agricultural products because of the superiorities of large penetration depth and volumetric heating, as well as high thermal efficiency (Liao, Damayanti, Xu, et al., 2020; Liao, Damayanti, Zhao, et al., 2020; Zhang et al., 2023), which are important considerations for industrial processing. Recently, RF heating in combination with conventional hot air drying techniques has been widely applied in agricultural products to improve drying efficiency and obtain high-quality products, including rice (Mahmood et al., 2023), shelled hazelnuts (Chen et al., 2021; Wang et al., 2020), carrot cubes (Gong et al., 2020), wheat germ (Liao, Damayanti, Xu, et al., 2020; Liao, Damayanti, Zhao, et al., 2020), and corn seeds (Xie et al., 2020). Indica-japonica hybrid rice (IJHR) is obtained by hybridizing indica rice and japonica rice, which has been widely cultivated due to its outstanding interspecific hybridization, and the yield improvement is perfectly meaningful compared to conventional rice varieties (Yin et al., 2021). Recently, most studies on IJHR have focused on cultivation and yield (Xu et al., 2020; Zhou et al., 2023), while sparse information is available about the effect of the drying processes on the protein structural and functional properties of IJHR. Therefore, as a new variety with high yield, the nutritious characteristics of IJHR will attract increasing attention from researchers, consumers and rice industrialists.

With its wide application in food processing, the effect of RF heating on the physicochemical properties of proteins from various sources has attracted increasing attention. RF energy is a high-frequency alternating electromagnetic wave, and polar groups of protein molecules can absorb electromagnetic energy during RF heating; thus, the conformation and advanced structure of protein molecules are strongly disturbed by electromagnetic waves, which might lead to aggregation and unfolding of the protein (Zhang et al., 2020), thus changing the structural and functional properties of the protein Guo et al. (2017) investigated the effect of RF heating treatment at different temperatures up to 90 °C on the structure of soy protein isolate. The obtained results showed that RF treatment did not modify the major structure of soy protein. Furthermore, Hassan et al. (2019) also showed that RF heating at different temperatures had no effect on the protein structure of maize while improving the oil-holding capacity and emulsifying properties of maize flour. Boreddy et al. (2016) found that RF-combined thermal processing heating at different temperatures (60, 70, 80 and 90 °C) improved the functional properties of egg white powder.

Rice protein is the most popular protein among all cereal proteins in terms of its amino acid structure because it contains the second highest content of lysine (D. Li et al., 2023). Compared with other plant proteins, rice protein is considered an efficient protein source because of its hypoallergenic property as well as its similar protein efficiency ratio to milk casein (Zhao et al., 2020). Several researchers have investigated the effect of RF treatment on protein structure and functional properties. However, little information is presented on the effects of different RF treatment times on the drying efficiency, protein structural, functional and thermal properties of IJHR during drying, especially compared to other drying processes. Based on this, this study was set up to investigate how different RF treatment times could affect the protein structural, functional and thermal properties of IJHR during drying.