Clove (Syzygium aromaticum) phenolics: extraction, compositions, and biological activities

Abstract

Clove herb is a tropical evergreen tree of Syzygium aromaticum L. Merr and Perry (syn. Eugenia caryophyllata, Caryophyllus aromaticus, L.). The herbal part is the unopened flower buds (Singletary, 2014). Clove belongs to the Myrtaceae family, which is native to India, Pakistan, and Indonesia (Chaieb et al., 2007; Maheswari et al., 2020). There are four key varieties of the clove: Ambon, Siputih, Zanzibar, and Sikotok, with the Zanzibar variety superiority to produce a higher amount of flowering buds than others considered the broadest cultivated variety (Alfikri et al., 2020). The clove tree has a vegetative cycle that can reach more than 100 years, with a height of 10–20m; also, it has smooth oval leaves and reddish flowers with several terminal clusters positioned at the end of the branches (Cort esRojas et al., 2014). Clove fruit has an elongated shape with a distinctively strong aroma (Cort es-Rojas et al., 2014). Clove buds are among the richest sources of clove plant parts in dietary phenolics with several uses in traditional medicine (Issac et al., 2015). Phenolic compounds, also known as polyphenols, are ubiquitous molecules in the vegetable kingdom and occur in a rich, diversified range of structures with a well-known essential role for plants growth and reproduction and specific function to protect injured plants against pathogens (Chiorcea-Paquim et al., 2020). Phenolic compounds are one of the largest secondary metabolites groups containing one or more hydroxyl groups binding to aromatic compounds (Rampadarath et al., 2014). Major classes of phenolic compounds are flavonoids, phenolic acids (hydroxycinnamic and hydroxybenzoic acids), and tannins (Chew and Nyam, 2019). Hydroxycinnamic acid derivatives include caffeic, ferulic, and p-coumaric acids with C3-C6 structure (Ramadan, 2019), meanwhile hydroxybenzoic acids derivatives such as gallic, syringic, and vanillic acids with C1-C6 skeleton (Boualem et al., 2017). Phenolic compounds possess a wide range of biological activities, including anti-allergic, anticarcinogenic, anti-inflammatory, antimutagenic, modulating enzymatic activities, pharmacological actions against oxidative damage diseases, including age-related diseases, coronary heart disease, and strokes (Chiorcea-Paquim et al., 2020). The reported biomolecular mechanisms for their action include angiogenesis inhibition, binding of electrophiles, apoptosis rate increment, H-donation, inhibition of cellular proliferation, reactive oxygen species (ROS) inactivation, protective enzymes induction, lipid peroxidation inhibition, and inhibition of DNA oxidation (Patil and Masand, 2018; Chiorcea-Paquim et al., 2020). This chapter provides an overview of the clove (Syzygium aromaticum) phenolics composition, structure, and biological activities, as well as their reported mode/mechanism of action.