**3. Bioactive compounds of ginger**

Ginger, the rhizome of *Zingiber officinale* Roscoe that belongs to Zingiberaceae family, is commonly used as a spice or dietary supplement and has been widely used in traditional medicine throughout history [40]. Ginger has been identified as having a multitude of different bioactive compounds, including lipids, carbohydrates, terpenes, and phenolic compounds, and its pharmacological effects are largely due to phenolic compounds and terpenes [41, 42]. Ginger-derived terpenes (α-zingiberene, camphene, ar-curcumene, β-phellandrene, E-α farnesene, β-bisabolene, α-piene) [43] are known to have antioxidant, anti-inflammatory, antibacterial, antidiabetic, analgesic, gastroprotective, neuroprotective, and anti-carcinogenic properties [41]. Of the 400 types of compounds present in ginger, four phenolic compounds are mainly responsible for its pharmacological effects: gingerols, shogaols, paradols, and ZGR [44, 45]. There are also other types of compounds related to gingerol (8-gingerol, 10-gingerol, and 12-gingerol) and shogaol (1-dehydrogingerdione, 6-gingerdione, and 10-gingerdione) [42].

The main pungent and most abundant compound, 6-gingerol, which is present in fresh ginger, attenuates various chronic disorders. By dehydration and after long storage, this compound is converted into 6-shogaol, which is more stable and has greater pharmacological effects than its precursor 6-gingerol [46, 47]. 6-Shogaol is converted to 6-paradol by bacterial metabolism, and both possess similar antiinflammatory and antioxidant properties [40, 47]. Antioxidant, antitumoral, antilipidermic, antibacterial, and anti-inflammatory actions are attributed to ZGR, and it is synthesized by reverse aldolization of gingerols when heating fresh ginger [47, 48]. **Figure 1** summarizes the metabolization pathways of 6-gingerol as a function of thermal processing.

**Figure 1.** *Properties and metabolism of gingerols.*

Zick et al. [49] observed that 6-shogaol and the 6-, 8-, and 10-gingerols have good bioavailability when consumed orally, being detected as sulfate and glucuronide conjugates. However, 6-gingerol has not been detected free in plasma after an oral dose of 2 g, despite it being the major compound in ginger extracts (2–64%) [50]. Pharmacokinetic studies showed that the half-life of the major compounds of ginger and its metabolites is approximately 1–3 hours. Based on bioavailability data, 6-, 8-, and 10-gingerol glucuronides and sulfates along with 6-shogaols could be good markers of ginger intake [50].

As for its therapeutic use, given its various anti-inflammatory, antimicrobial, anticancer, and antioxidant biological activities, ginger appears to be effective in the prevention and treatment of neurodegenerative, cardiovascular, obesity, diabetes mellitus, or respiratory disorders [45].
