**1. Introduction**

Ginger is a widely cultivated food and medicinal crop in many parts of the world. It is amongst the most widely used spices globally [1]. It was first cultivated in Ethiopia in the 1200s and continues to be cultivated despite challenges of low quality, reduced economic output and poor handling by farmers and sellers [2]. Although with similar health benefits as fresh ginger, ginger essential oil is said to be the most potent portion of ginger [3].

The essential oil of ginger is the yellowish or green coloured volatile oil extracted from ginger rhizomes, which is about 1–3% of a rhizome. It may be obtained from fresh ginger rhizome, dried rhizomes or ginger peel, with oil from the fresh ginger reported to be of better fragrance than that from dried ginger [4, 5]. As it is known with spices, ginger oil is generally regarded as safe [GRAS] [6, 7]. It is known as the oil of empowerment because it gives the user a feeling of self-assurance and courage [3].

Ginger oil may be extracted from ginger rhizomes in different ways. It can be obtained traditionally (when it is crushed, macerated in water for about 12 h, heated with sesame oil, filtered and centrifuged), conventionally (crushed, macerated in sesame oil for 7 days, filtered and centrifuged) or by hydro distillation (with the use of Clevenger-type apparatus) [8]. GC–MS analysis of ginger essential oils shows its major constituents to be Zingiberene, β-bisabolene, ar- curcumene, camphene, citral and geranial [5].

The volatile oil of ginger possesses extensive biological effects. The essential oil of ginger has been indicated as an antispasmodic, anti-inflammatory, antinociceptive and antioxidant agent [9–12]. It has also been used in the treatment of joint stiffness and pain [13] as well as a tonic for the uterus, brain and the stomach [14]. In addition, it is useful in managing respiratory disorders [15], relieves anxiety and is heart and liver friendly [16–18]. In fact, it has been proffered that the benefits derived from the use of essential oils of ginger is similar to that derived from fresh ginger [3], suggesting that the chemical constituents of fresh ginger are retained in its oils. It possesses antiseptic, antimicrobial, healing, anti-nausea and anti-stress properties and is thus employed in facilitating healing after surgical procedures [19, 20]. It aids digestion and is used in the treatment of stomach disturbances [21]. In addition, the essential oil of ginger is useful as a flavouring, preservative, perfumery and pesticidal agent [22]. These properties have been attributed to the volatile constituents such as monoterpenes and sesquiterpenes and pungent fractions of ginger, specifically, shogaols, gingerols and paradols [23]. The constituents of ginger essential oil are however affected in composition, potency and quantity by place, duration and region of cultivation, thus affecting its bioactivity, colour, aroma and ultimately its use.
