Effect of blanching and microwave-hot air drying of Asparagus racemosus Willd. tuberous roots on shelf life

Abstract

The quality of dried tuberous roots of Asparagus racemosus Willd. depends on the drying method and storage conditions. This research aims to compare three methods for drying blanched and non-blanched root slices: tray drying at 60 °C (TD 60 C), microwave-assisted hot air drying at 1000 W with 60 °C (MW1000+60 C), and at 1500 W with 60 °C (MW1500+60 C). Drying efficiency was evaluated over a one-year shelf life. The blanching was carried out at 80 °C for 5 min. MW1000 60 C was the most suitable for brightness, total phenolic content (TPC), total flavonoid content (TFC), total saponin content (TSC), and sugar content. Its brightness (L*), TPC, TFC, and TSC were 90.90 ± 1.08, 1.96 ± 0.08 mg GAE/g DW, 0.69 ± 0.07 mg ECE/g DW, and 1256.8 ± 25.1 mg SE/g DW, respectively. Total sugar content and total reducing sugar content were 1577.1 ± 17.1 mg Glu/g DW and 47.43 ± 2.06 mg Glu/g DW, respectively. Blanching before MW1000+60 C decreased TPC, TFC, total sugar content, and total reducing sugar content by 31 %, 25 %, 20 %, and 43 %, respectively, but did not reduce the TSC. The optimum shelf life was 6 months. The storage for 12 months caused negative changes in moisture content, colour, TPC, TFC, sugar content, and microbial load. The saponin compounds were asparacoside, shatavarin IX, shatavarin V, asparanin A, aspafilioside B, and sarsasapogenin 3-[4''-glucosyl-6''-arabinosylglucoside]. Theasaponin E3 was found in blanched and dried roots after 12 months. Consequently, this research provided guidelines for drying methods and monitoring shelf life.