Pretreatment With Dense-Phase Carbon Dioxide Improves Jujube Quality After Hot-Air/Microwave Drying

Jujube is widely recognized as a highly nutritious food. However, due to its high moisture content at the harvesting stage, efficient drying techniques are typically required for extending its shelf life and maintaining quality. This study investigated the effects of three pretreatment strategies-nonthermal dielectric-barrier discharge plasma (plasma), alkaline ethyl oleate (AEEO), and dense-phase carbon dioxide (DPCD) treatment-on the drying kinetics, energy consumption, and final quality of jujubes dried using a coupled hot-air/microwave system. All pretreatments significantly enhanced the drying rate of jujubes, with the AEEO group exhibiting the most rapid drying. In this group, the total drying time was 33.3% lower than that in the control group. Color analysis revealed an increase in the a* value across all pretreated samples. However, the DPCD group demonstrated the smallest total color difference (ΔE*) when compared to fresh jujube samples, reflecting the superior color preservation in this group. Moreover, DPCD-treated samples also retained the highest levels of bioactive compounds, including vitamin C, total phenols, and flavonoids, thus achieving the strongest antioxidant and free radical-scavenging capacity. Microstructural observations revealed that DPCD created a porous tissue structure in jujubes, facilitating moisture migration. Although thermal treatment generated the most diverse profile of volatile aroma compounds in jujubes, it provided a slower drying rate. Meanwhile, despite achieving the fastest drying rate, AEEO led to the significant (p < 0.05) degradation of bioactive components. Therefore, DPCD can effectively combine accelerated drying with superior retention of product quality and nutritional value. These findings highlight the potential of DPCD for the industrial-scale production of high-quality dried jujubes.