**1. Introduction**

Turmeric *(Curcuma longa* L.), belonging to Zingiberaceae, is a rhizomatous plant native to Southeast Asia, but is extensively cultivated worldwide, particularly in tropical countries (e.g., India, Pakistan, Bangladesh, China, Taiwan, Thailand, Sri Lanka, East Indies, Burma, Indonesia, northern Australia, Costa Rica, Haiti, Jamaica, Peru, and Brazil) [1–4]. Turmeric is well known for its use as a culinary ingredient and a traditional herbal medicine [5]. It is extensively used in Asian cuisine and is one of the key ingredients in curry powders [6]. Turmeric, either fresh or in dried form, has a long history of medicinal use, dating back 4000 years [7]. Due to its bright yellow/orange color, turmeric is often referred to as the "Indian saffron" or "golden spice". Curcuminoids are considered the main bioactive components of turmeric. Turmeric's medical properties are credited mainly to the curcuminoids, which are abundant in turmeric rhizome [8]. The total curcumin (sum of all curcuminoids) was proven to have significant health benefits along with the potential to prevent various diseases, including Alzheimer's, coronary heart disease, and cancer [9]. Due to a plethora of scientific articles on the health benefits of turmeric, the demand for turmeric is steadily increasing in the US and now represents an estimated US\$36 million per annum. The US imports 90% of its requirements from various countries [10]. Due to recent inconsistencies associated with quality and production methods of raw materials imported from Asian countries, many US manufacturers of herbal products are seeking domestically-produced materials that meet their standards and requirements. Turmeric (*Curcuma longa*) is one such crop. The rhizome from which the curcumins are derived is tuberous, with a rough and segmented skin. The primary rhizome is called the "mother rhizome" or bulb, which is

**Citation:** Setzer, W.N.; Duong, L.; Poudel, A.; Mentreddy, S.R. Variation in the Chemical Composition of Five Varieties of *Curcuma longa* Rhizome Essential Oils Cultivated in North Alabama. *Foods* **2021**, *10*, 212. https://doi.org/10.3390/foods 10020212

Academic Editor: Severino De Alencara Received: 4 December 2020 Accepted: 18 January 2021 Published: 21 January 2021

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pear-shaped in the center (Figure 1). The branches of mother rhizomes are the secondary rhizomes, called lateral or "finger rhizomes" [11]. The mother rhizomes are more matured than finger rhizomes, therefore containing higher curcuminoid concentrations and perhaps higher essential contents than finger rhizomes. However, the curcumin yield from finger rhizomes is higher than that from mother rhizomes [12].

**Figure 1.** Underground parts of *Curcuma longa* showing the rhizomes and roots.

One of the important components of turmeric is its volatile oil. The role of turmeric oil in the treatment of a wide variety of diseases in animals and humans were reviewed in detail [4,7]. Thus, curcuma oil appears to be a promising agent for the treatment of simple dermatitis, cerebral stroke, and other disorders associated with oxidative stress [13]. The essential oils of turmeric are relatively complex, with hundreds of components. The major components, however, are α-turmerone (12.6–44.5%), β-turmerone (9.1–37.8%), *ar*-turmerone (12.2–36.6%), β-sesquiphellandrene (5.0–14.6%), α-zingiberene (5.0–12.8%), germacrone (10.3–11.1%), terpinolene (10.0–10.2%), *ar*-curcumene (5.5–9.8%), and α-phellandrene (5.0–6.7%) [14].

Turmeric is considered a viable cash crop with a ready market in Alabama and in the US. Similar to any essential oil crop, turmeric's essential oil also varies with variety, soil type, and environmental conditions [15,16]. Hence, evaluating different varieties for essential content and composition is an important consideration for determining a variety for cultivation in a particular location. Turmeric is a tropical crop and grows well in warm and humid environments with mean air temperatures between 20 and 30 ◦C. It can be planted in all soil types, but it does best in well-drained clay loam or sandy loam soils

rich in humus or organic matter with a soil pH of about 5.5 to 6.5. It grows in a wide range of climatic conditions but requires about 100 to 200 cm of rainfall a year. Thus, Alabama's hot, humid, and rainy summer season is suited for turmeric production in the southeastern US. Furthermore, turmeric is potentially suited for catering to the herbal products industry, which prefers locally sourced materials. The purpose of the present study was to determine the variation in the essential oil chemistry of five *C. longa* genotypes that could potentially be cultivated for commercial purposes in north Alabama and to note any differences between the mother rhizome and the lateral rhizomes of each cultivar.

#### **2. Materials and Methods**

#### *2.1. Curcuma longa Varieties*

The five varieties used in this study were selected out of fourteen varieties according to three criteria: high yield but low curcuminoid content (varieties, CL5, CL3), low yield but high curcumin content (CL10), and high yield and high curcumin content, thus, high curcumin yield (CL9, CL11), based on studies at Auburn University and Alabama A&M University. Thus, CL3 and CL5 may be considered for the fresh rhizome market, CL 10 for the high curcumin dry rhizome herbal products market, and CL9 and CL11, which have attractive, orange-colored rhizomes, could serve both fresh and dry herbal produce markets. The two varieties CL3 and CL9 were consistent in their performance over three years in both south and north Alabama. A knowledge of their relative oil yield and composition could help in value-addition for either fresh rhizomes or dry herbal markets.
