UHPLC-MS/MS and GNPS Elucidate Gallic Acid Transformation and Accumulation Mechanism in Phyllanthus emblica L. during Hot Air Drying

Phyllanthus emblica L. is a fruit with high medicinal and edible value. Its main bioactive component, gallic acid (GA), is significantly increased by hot air drying, yet the underlying chemical mechanism remains unclear. This study investigated the temperature-dependent transformation of phenolics during drying (80–130 °C) using UHPLC-MS/MS and Global Natural Products Social Molecular Networking (GNPS). High-temperature drying (110 to 130 °C) increases the GA content by 13.4–26.9 fold. Integrated metabolomic analysis suggests this accumulation results primarily from two nonenzymatic pathways: the thermal hydrolysis of glucose galloyl derivatives (e.g., glucogallin, digalloylglucose, and trigalloylglucose), and the degradation of glucuronic acid galloyl derivatives (e.g., 2-O-galloylgalactaric acid and monogalloylgalactonolactone). While temperatures >110 °C maximize gallic acid yield, the Maillard reaction products (e.g., 5-HMF) were also promoted. These findings elucidate the chemical mechanism of GA accumulation via ester bond cleavage, providing a scientific basis for optimizing drying protocols to balance medicinal quality and safety.