Comparative Evaluation of Phenolic Composition and Antioxidant Activities of Gastrodia elata Rhizome Cultivated in the Indoor Facility and Outdoor Field: Effects of Cultivation Type, Growth Stage and Harvest Season

Gastrodia elata rhizome (GER), long used medicinally and as food in East Asia, is now produced via outdoor field (OFC) or indoor facility (IFC) cultivation. This study evaluated phenolic composition and antioxidant properties of GER by cultivation method, growth stage, and harvest season. Seven compounds were quantified by HPLC; parishin A, parishin B, parishin E, and p-hydroxybenzyl methyl ether (p-HBME) were the major constituents. Among mature samples, their total content ranged from 13.21 to 18.33 mg/g DW in OFC-grown GER and was 12.15 mg/g DW in IFC-grown GER, while immature GER contained up to 26.16 mg/g DW. However, IFC and OFC samples originated from different regions, so differences cannot be attributed solely to cultivation method. Spring-harvested GER had a higher total content of the seven compounds than autumn-harvested GER (20.67 ± 0.17 and 12.01 ± 0.19 mg/g DW, respectively) and stronger DPPH, FRAP, and ABTS activities, whereas total phenolic content (TPC) was higher in autumn. Seasonal comparisons reflect extraction replicates of composite samples, not independent biological replicates. ABTS activity was positively correlated with gastrodin, 4-hydroxybenzyl alcohol (4-HBA), p-HBME, parishin A, and total flavonoid content (TFC). PCA explained 71.5% of total variance (PC1–PC2), supporting discrimination among GER samples by phenolic and antioxidant profiles.