Valorisation of Zingiber officinale hydrodistillation residual cake as a sustainable source of bioactive gingerols and shogaols: Quantification by validated HPLC-DAD and multi-spectroscopic characterization

Zingiber officinale Roscoe (ginger) hydrodistillation for essential oil production generates large quantities of residual cake, an underutilized by-product rich in non-volatile phenolics. This study characterized and quantified gingerols and shogaols in fresh Ecuadorian ginger rhizomes ( FZO ) and residual cakes from laboratory ( GRC-L1–3 , 1.5–2.5 h) and industrial-scale ( GRC-CH , ∼10 h) hydrodistillation. Proximate analysis showed depletion of ash, fat, protein, and fiber in residues, with relative enrichment in carbohydrates (NFE up to 78.04% dry basis). UV-Vis, fluorescence, and FTIR spectroscopy (with PCA) provided supporting qualitative evidence for differences in phenolic composition. A validated isocratic HPLC-DAD method (C18, 65:35 acetonitrile:water + 0.1% formic acid, 282 nm) showed excellent linearity for external calibration curves (R² ≥ 0.9915), precision (%RSD <2%), and recovery (81.6–118.9). Fresh rhizomes contained ∼3.15 mg g⁻¹ total gingerols (6-gingerol dominant). The industrial cake retained ∼2.59 mg g⁻¹ gingerols but showed the highest shogaol content (∼1.01 mg g⁻¹). These findings highlight ginger hydrodistillation residues as a promising sustainable sources of bioactive compounds for nutraceuticals, and cosmeceuticals in a circular economy framework.