Gallic Acid Derivatives Are the Active Ingredients of the Optimized Phenolic Extracts of Chinese Tallow Tree

The Chinese tallow tree (Sapium sebiferum (L.) Roxb) (CTT) is a valuable forest resource, and its leaves have long been utilized in Traditional Chinese Medicine for the treatment of various diseases, primarily due to the antioxidant activity of phenolic compounds. In this study, a simple ultrasonic-assisted phenolic extraction method was established using response surface methodology. The highest total phenolic content was obtained by extracting with 40% ethanol (v/v) in a solid-liquid ratio (g/mL) of 1:48 for 20 min at 30°C, employing an ultrasonic bath with a power of 270 W and a frequency of 40 kHz. Using the optimized phenolic extract, a non-target metabolomics approach was adopted to evaluate the antioxidant ingredients of the CTT. Most of the identified phenolic compounds were depleted after reacting with free radicals, indicating their significant contribution to the antioxidant activity of CTT leaves. Among them, gallic acid derivatives, geraniin, and ethyl gallate were identified as the predominant antioxidant ingredients. Overall, a simple ultrasonic-assisted phenolic extraction method was optimized, and the antioxidant ingredients of the valuable CTT leaves were identified. These findings significantly promote the development and application of CTT leaves.