Comparative evaluation of quality characteristics of fermented napa cabbage subjected to hot air drying, vacuum freeze drying, and microwave freeze drying

Fermented napa cabbage (FNC) is a traditional probiotic-enriched food. In this study, the potential of different drying techniques, including hot air drying (HAD), vacuum freeze drying (FD), and microwave freeze drying (MFD), for the production of dehydrated FNCs was evaluated. To reach a moisture content of 0.12 g⋅ g−1 (d.w.b.), MFD took 2 h, which was half of the time needed for HAD. FD process required the longest drying time, which was 18 h. Therefore, MFD consumed significantly less power compared to FD and HAD, which was 12.63% of FD power usage and 30% of HAD power usage. Both MFD and FD products exhibited better rehydration ability than the HAD product due to their honeycomb-like structure with less shrinkage. MFD and FD were able to preserve the living probiotics, bioactive components, and antioxidant capacities of FNCs better than HAD. The taste and aroma of dehydrated FNC products were maintained better by microwave-induced oxidation reaction and Maillard reaction during MFD treatment, based on the quantitative results regarding amino acids, volatile compounds, and sensory evaluation. In general, MFD is a promising method for obtaining high-quality dehydrated FNCs as probiotic foods.