Effect of different drying methods on the quality of restructured rose flower (Rosa rugosa) chips

Rose flower chips were produced by freeze drying (FD), pulse spouted vacuum-microwave freeze drying (PSVMFD), vacuum-microwave freeze drying (VMFD), and microwave-assisted vacuum drying (MVD). Drying time, color attributes (L*, a*, b* and h), flavor, texture, Vitamin C, flavonoids content, shrinkage value, DPPH radical scavenging capacity, and microstructure were compared. Results showed that MVD was the fastest (120 min) method of drying and FD was the slowest (560 min) method to achieve the target moisture content (under 5%). Considering product quality, FD samples exhibited the highest vitamin C (2.40 +/- 0.14 mg/100 g) and flavonoids content (88.33 +/- 0.22 mg/100 g), with the strongest DPPH radical scavenging capacity, followed by PSVMFD samples. Additionally, FD samples showed the lowest shrinkage (3.89 +/- 0.01%) followed by PSVMFD samples (15.02 +/- 0.02%) whereas the MVD chips had the highest shrinkage (50.12 +/- 0.12%). FD and PSVMFD samples exhibited loose porous structure, while VMFD and MVD samples showed more compact structure. Considering the drying time and product quality comprehensively, PSVMFD was a novel and promising drying method to produce high quality rose flower chips.