Comparative assessment of drying techniques on the quality of millet (Sorghum bicolor) microgreens

Microgreens are increasingly popular due to their unique nutritional profile, diverse phytochemical composition, and intense flavor. Considering their rapid senescence, this study examined oven drying (OD), conductive hydro drying (CHD), and freeze-drying (FD) to retain the quality of sorghum microgreens. All dried samples exhibited quality changes, with fresh (F) samples serving as the control. FD sample resulted in low moisture (4.34 ± 0.08) and water activity (0.42 ± 0.01), as well as the highest phenolic (40.92 ± 0.18 mg/g) and flavonoid (10.10 ± 0.12 mg/g) contents. Both FD and CHD yielded excellent flow properties; CHD provided higher ascorbic acid retention (12.42 ± 0.38 mg/g). F had 58.42 mg/100 g of total chlorophyll and 5.97 mg/100 g of carotenoids, and the FD sample retained highest pigment content (54.62% more than OD, 42.22% more than CHD). The Midilli-Kucuk kinetic model demonstrated the best fit (R² > 0.99). In summary, while FD offers a higher quality, CHD is a time- and cost-effective technique.