Introduction

Plant phenols are a main class of chemicals that contain one or more hydroxyl groups on their benzene skeleton and are composed of 8000 different phenolic structures. They are broadly distributed in the plant kingdom and are the most abundant secondary metabolites of natural plants, which cover from simple molecules (such as phenolic acids) to highly polymerized structures (such as tannins and lignin, see Fig. 1.1). Several typical plant phenolic compounds include eugenol, vanillin, ferulic acid, cardanol, urushiol, and catechol (Lu et al., 2022). Due to their unique chemical structure and attractive properties, they have been widely used in various fields of industry, including antioxidants, UV screens, functional materials, biomedical devices, and food ingredients.