Improvement of <i>Larimichthys crocea</i> Drying Using Radio Frequency Combined Hot Air Treatment: Dielectric Properties, Drying Kinetics, Quality Attributes, and Flavor Profiles

This study evaluated the potential of radio frequency combined hot air drying (RFHAD) on Larimichthys crocea, focusing on its dielectric properties, drying kinetics, quality attributes, taste-active compounds, and volatile flavor compounds. RFHAD (50 °C, electrode gaps of 8.0, 8.5, and 9.0 cm) significantly reduced the drying time by 33.53–54.12% compared to hot air drying (50 °C, HAD) and offered better heating uniformity than radio frequency drying (electrode gap of 8.5 cm, RFD8.5). RFHAD8.0 and RFHAD9.0 caused a more severe lipid oxidation to L. crocea than HAD and RFD8.5, while RFHAD8.5 exhibited comparable levels of malondialdehyde and peroxide value to RFD8.5. The water activities in RFHAD8.0 and RFHAD8.5 were significantly decreased relative to the other three dried samples. Compared to HAD, the levels of L*, b*, and C were dramatically increased under the RF cotreatment at 8.0 and 8.5 cm, showing a bright yellow appearance. Texture parameters showed that RFHAD treatment improved the softness of the dried L. crocea while alleviating the springiness and resilience declines caused by RF energy. Furthermore, the taurine contents in the RFHAD samples were significantly higher. Taste profile analysis revealed that RFHAD8.5 resulted in an improved umami taste, with equivalent umami concentration values 1.77 and 1.23 times that of the HAD and RFD8.5 groups, respectively. Moreover, RF energy could significantly reduce the formation of bitter free amino acids. The alcohols (1.26 times) and esters (1.55 times) were significantly elevated by RFHAD8.5 compared to RF energy alone, contributing a more pronounced pleasant odor. The oily, disagreeable, and sour components, including 3-methyl-1-butanol, 2-methyl-1-propanol, and acetic acid, found in HAD-dried samples were effectively reduced by RFHAD8.5 treatment. However, an elevation in the levels of aldehydes was observed in the RFHAD8.5 samples relative to the HAD and RFD8.5 ones, which may produce undesirable odors. This study indicates that RFHAD is a promising technique for processing high-quality dried fish, offering a high drying rate and improved heating uniformity.