Evaluation of freeze drying combined with microwave vacuum drying for functional okra snacks: Antioxidant properties, sensory quality, and energy consumption

- The main quercetin and epigallocatechin in okra fruit were identified and quantified.
- FD-MVD was first applied in functional okra snacks.
- Comprehensive evaluation of quality and energy consumption was built by PCA.
- FD-MVD is very promising for functional okra snacks in good quality and cost saving.

This study evaluated freeze drying combined with microwave vacuum drying (FD-MVD) for functional okra snacks. FD-MVD was compared using four different drying methods: hot air drying (AD), freeze drying (FD), microwave vacuum drying (MVD), and hot air drying combined with microwave vacuum drying (AD-MVD). For main antioxidant components including epigallocatechin gallate (EGC), epicatechin gallate (EGCG), epigallocatechin (ECG), quercetin 3-O-diglucoside, and quercetin 3-O-(malonyl) and antioxidant properties (IC50, AEAC, FRAP, ABTS, TF, and TPC) and color (L*, a*, and b*), the values of FD-MVD were similar to those of FD and significantly higher than those of AD, MVD, and AD-MVD (P < 0.05). Compared to FD, FD-MVD provided moderate hardness (22.43 ± 1.18 N) and crispness (6.74 ± 0.87 N), and reduced the drying time and energy consumption by approximately 75.36% and 71.92%, respectively. Principal component analysis (PCA) of physicochemical and drying efficiency indexes indicated that FD-MVD is a promising technique for the processing of functional okra snacks.