Particle Size Reduction to Nanoscale Modulates Extraction Yield, DPPH Radical-Scavenging Activity, and Metabolite Profile of Red Ginger Powder (Zingiber officinale Var. rubrum).

This study evaluated the effect of particle size reduction of red ginger (Zingiber officinale var. rubrum) powder on extraction yield, DPPH radical-scavenging activity, and chemical profile. Powders with D50 ranging from 2256 to 0.22 µm were extracted using methanol and analyzed for yield, DPPH radical-scavenging activity, ATR-FTIR fingerprint, and metabolite composition using LC-HRMS. Multivariate analysis was applied to correlate spectral features with DPPH radical-scavenging activity. Particle size reduction significantly increased extraction yield from 3.36% ± 0.26% to 10.31% ± 0.20%. However, the DPPH radical-scavenging activity expressed per gram of extract showed a non-linear trend, with the highest value observed in coarse particles (18.10 ± 1.42 mg TE g-1 extract), decreasing at microscale, and partially recovering at nanoscale (15.88 ± 0.44 mg TE g-1 extract). ATR-FTIR combined with OPLS identified spectral features associated with the DPPH radical-scavenging activity, including O─H, C═O, aromatic C═C, and C─O vibrations, indicative of phenolic ketone structures. LC-HRMS profiling indicated particle-size-associated compositional differences, including lower relative 6-gingerol signals and higher relative shogaol-related signals at the microscale, as well as higher relative lipid-related signals at the nanoscale. Particle size reduction modulates both extraction efficiency and chemical selectivity. While nanoscale processing enhances extract recovery, it alters metabolite composition and reduces DPPH radical-scavenging activity per unit extract, highlighting a trade-off between extract yield and DPPH radical-scavenging activity per unit extract. PRACTICAL APPLICATIONS: Reducing the particle size of red ginger powder to the nanoscale substantially increases the extraction yield. Therefore, planetary ball milling remains an efficient strategy for maximizing the utilization of red ginger raw materials in the food and nutraceutical industries.