Freeze- and oven-drying of red ginger juice (Zingiber officinale var. Rubrum): A comparative study on physicochemical properties, bioactive retention, and microstructural characteristics

• Effects of drying methods and temperatures on red ginger juice were evaluated. • Freeze-drying retained most 6-gingerol but had a long drying time and low yield. • Oven-drying at 50°C gave good drying time and preserved key bioactives. • Drying temperature ≥ 60°C degraded 6-gingerol and reduced antioxidant activity and color. • SEM showed that freeze-dried samples had better microstructure than oven-dried ones. This study evaluates the influence of drying methods and oven drying temperatures on the physicochemical properties, bioactive compounds, and microstructure of red ginger ( Zingiber officinale var. Rubrum ) juice powder. Two drying techniques were applied, freeze-drying (FD) and oven-drying (OD) at 40 °C to 80 °C. FD preserved the highest levels of bioactive compounds, particularly 6-gingerol, but required prolonged drying (63.0-72.0 hours) and yielded lower product mass. In contrast, OD at 50 °C provided the best compromise between processing efficiency (9.3-10.0 hours) and quality retention, maintaining high levels of total phenolic content (TPC), 6-gingerol, and antioxidant activity. Drying at ≥ 60 °C caused 6-gingerol degradation into 6-shogaol, reducing antioxidant capacity and altering color due to Maillard reactions. Scanning electron microscopy (SEM) revealed that FD retained intact microstructures, whereas OD at higher temperatures induced porosity and fragmentation. Overall, OD at 50 °C is recommended as a practical and effective method for producing high-quality red ginger juice powder on an industrial scale.