*2.2. Phytochemistry and Health Benefits*

With increasing interest in the therapeutic applications of natural products, ginger has received much attention in recent years, with numerous studies and reviews exploring its phytochemistry, pharmacological, and health-benefiting properties [14,21–26]. Overall, ginger is rich in phytochemicals, with over 300 identified constituents divided into three main categories: gingerols, volatile oils, and diarylheptanoids, as reported by Liu et al. [27]. The most notable are the phenolic compounds in gingerols, shogaols, and paradols, including 6-gingerol, 6-shogaol, 8-gingerol, 8-paradol, 10-gingerol, and many more [28]. These compounds are responsible for the unique pungent smell and taste of ginger. Other gingerolrelated compounds include zingerone, gingerenone A, and 1-dehydro-10-gingerdione [29]. In addition, the volatile oils of ginger also contain terpene compounds such as *β*-bisabolene, *α*-curcumene, zingiberene, *α*-farnesene, and *β*-sesquiphellandrene [30]. The ginger's diarylheptanoid contents can be divided into linear diphenyl heptane and cyclic diphenyl heptane compounds with antioxidant activity [27].

Ginger is also known to contain many secondary metabolites of flavonoids and other phenolic components such as quercetin, rutin, catechin, epicatechin, kaempferol, naringenin, fisetin, morin, hesperidin, salicylic acid, and chlorogenic acid [31–33]. The concentrations of these secondary metabolites in ginger may vary significantly across samples as their contents are influenced by the environmental conditions (including light intensity, temperature, insects, etc.) where ginger is grown and methods of drying and storage. Higher pheno-

lic and flavonoid content in ginger is known to increase its antioxidant activities [34,35]. Figure 1 provides an overview of ginger and its constituents.

**Figure 1.** An overview of ginger and its main groups of active constituents of gingerols, volatile oils, diarylheptanoids, and flavanoids with some sample structural formulas. In the formulas of gingerols, <sup>n</sup> denotes the number of repeating units of CH2. R1, R2, and R3 in the selected diarylheptanoid structures are sites for functional groups or substituents (e.g., H, CH3, OCH3, or COCH3).

Among these constituents, 6-gingerol is the most pharmacologically active compound [26], whereas 6-shogaol has a higher potency than 6-gingerol in terms of bioactivities but exists in a lesser quantity naturally [36]. By studying ginger's typical metabolic pathways in a mouse model, the in vivo effects were found to derive mainly from 6-gingerol and 6-shogaol, with hydrogenation, demethylation, glucuronidation, sulfation, and thiolation being their major metabolic reactions [16]. Shogaols are metabolised through more complicated pathways than gingerols, and these two compounds have different molecular targets even though both are reported to have potent antioxidant and anti-inflammatory actions [37].

The pharmacological effects of ginger and its active compounds have been recently reviewed by many authors, including Unuofin et al. [23], Mao et al. [28], and Choi et al. [38]. Notable effects include anti-diabetic [39–41], anti-emetic [42–44], anti-nauseant [45,46], antiobesity [47–51], anti-inflammatory [52–55], antioxidant [56–60], nephroprotective [61–63], neuroprotective [64–66], gastroprotective [67,68], and anti-melanogenesis [69,70] effects. Moreover, ginger may also be protective against male infertility [71]. The anti-inflammatory and antioxidant activities of ginger extract, and 6-gingerol in particular, have also been shown to have antiproliferative and anticancer properties in another review by de Lima et al. [26]. For clinical application, a systematic review of 109 randomised controlled trials (RCTs) by Anh et al. [25] found evidence to support the use of ginger for improvement in nausea and vomiting in pregnancy, inflammation, metabolic syndromes, digestive function, and colorectal cancer markers.
