1. Introduction
The nutmeg plant has fruit, seeds and flowers which can be extracted as very important commodities. Parts of the nutmeg plant such as flowers, fruit (flesh and seeds) are widely used in cosmetics, medicine, beverage, perfume, aromatherapy, and food industries. Nutmeg oil extracted from nutmeg seeds can be used as a raw material for making soap, medicine, perfume, and aromatherapy [
1,
2,
3].
Nutmeg oil can be produced from nutmeg seeds through a distillation process. The method widely used for extracting nutmeg oil is Water Steam Distillation (WSD). Nutmeg oil is used by the pharmaceutical industry as a raw material for medicines, additives in food and drinks. Nutmeg oil contains chemicals such as myristicin, limonene, sabinene, alpha and gamma-terpinene [
4,
5]. Myristicin is a very important compound in nutmeg oil. The myristicin content in nutmeg oil
(Myristica fragrans) according to the ISO 3215:1998 standard is at least 10%. Myristicin levels also determine the quality of nutmeg oil. Other parameters to determine the quality of nutmeg oil are colorless or pale yellow, has a characteristic aroma of nutmeg oil, refractive index of 1.470-1.497, density of 0.880-0.910 g/mL, optical rotation +8-25
o, solubility in ethanol 90% (1:3) clear and maximum remaining evaporation is 2% [
6,
7].
The pharmaceutical industry widely uses nutmeg oil as a precursor. Based on research results, it shows that nutmeg oil has biological activity. Myristicin is a compound in nutmeg oil that has long been used as medicine. This compound has analgesic, antimicrobial, anti-inflammatory, hepatoprotective and antioxidant effects. This compound is also known as a hallucinogenic compound, namely a compound that acts as a serotonin receptor antagonist [
8,
9]. This compound also acts as a neurotoxic agent in neuroblastoma, namely by inhibiting monoamine oxidase. Myristicin used in excessive doses can cause damage to human organs. Symptoms caused by poisoning with this compound are nausea, seizures, delirium, blurred vision, and palpitations [
9].
Nutmeg oil refined by water steam distillation (WSD) meets SNI for export purposes. The weaknesses of the extraction process by water vapor distillation are low yield, long distillation time (24 hours), wasteful of fuel, wasteful of manpower, produces polluting gases which damage the environment and requires a lot of water as a coolant. Refining nutmeg oil by WSD yields little profit. Refining nutmeg oil by water steam distillation produces a yield of 9-10% [
10]. Because of these problems, the researchers proposed the use of a new extraction method are the supercritical fluid extraction (SCFE) method using CO
2 gas.
Extraction of nutmeg oil using WSD has many disadvantages such as long extraction time, uses a lot of fuel, is a source of air pollution and high costs. SCFE is a new extraction method that is more efficient and lower cost. This method does not produce air pollution gases and is environmentally friendly. SCFE requires little solvent, resulting in high yields and shorter extraction times. SCFE is very suitable for the extraction of materials that cannot withstand high temperatures and are sensitive to heat. CO
2 gas used in SCFE does not destroy ozone, is not flammable, safe for human health and environmental, reusable, inert, has high solubility, non-flammable, non-corrosive and is non-toxic. This gas is easy to apply and controlled with temperature changes. CO
2 gas works in a supercritical state which is influenced by temperature and pressure. Supercritical fluid is a fluid with a temperature higher than the critical temperature and a pressure higher than the critical pressure [
11].
SCFE is an extraction method based on the solubility of chemicals with supercritical CO2 liquid. This method can be used for the extraction of active ingredients from plants and animals. The CO2 gas that has been extracted is released and reused. This method is known as supercritical fluid extraction. SCFE can use carbon dioxide gas, sulfur hexafluoride, heptane, ammonia, ethane, and nitrous oxide. CO2 gas is often chosen for the SCFE process because it has several advantages such as being colorless, low critical temperature, chemically inert, easy to obtain in a pure state and cheap. CO2 gas is widely used to extract natural materials.
CO2 gas as an extractant is in a critical state at a temperature of 31.1 oC and a pressure of 7.38 MPa. Cheap operational conditions, suitable for materials that are sensitive to heat and high boiling points. Natural ingredients that are often extracted with CO2 gas include essential oils, spices, flavorings, and vitamins. CO2 gas is very stable, non-toxic, and does not cause products to oxidize. Extraction with CO2 gas does not contain nitrates, dangerous heavy metals and is free from dangerous residual solvents. CO2 gas is easily recovered in its pure state by changing the temperature and pressure. CO2 gas can be reused for the next process, so supercritical CO2 extraction is more efficient.
SCFE with CO
2 gas is an environmentally friendly extraction model [
12,
13,
14]. Several researchers have used the SCFE method for the extraction of essential oils such as extraction of turmeric [
15], cumin
(Carum carvi L.) [
16], sucupira branca seeds [
17], algerian rosemary [
18], lippia thymoides and Schauer
(Verbenaceae) [
19], Leptocarpha rivularis [
20], dry ginger [
21], candeia wood
(Eremanthus erythropappus) [
22], clove leaves
(Syzygium aromaticum) [
23], rosehip seeds [
24], Santolina chamaecyparissus [
25], perovskia atriplicifolia benth [
26] and chamaecyparis obtuse [
27].
Therefore, the SCFE method needs to be applied for the extraction of food, biological, pharmaceutical, and cosmetic ingredients. Materials containing aromatic compounds are very suitable for extraction using this method. The SCFE method can maintain aroma and increase product purity. This method is widely used to extract various types of seeds such as fennel, cumin, and celery. This method also has the potential to extract essential oils from various types of plants. The method can be used to extract essential oils such as jasmine, rose, cinnamon, ginger, chrysanthemum, and various types of spices. One of the essential oils with a lot of market demand is nutmeg oil. Meanwhile, nutmeg oil is obtained by water steam distillation (WSD). This method is widely used by nutmeg oil entrepreneurs. This method has many disadvantages, namely long extraction time (24 hours), requires a lot of fuel, complicated product separation and produces polluting gases. Therefore, it is necessary to carry out comparative research on nutmeg oil extraction using the WSD and SCFE methods. Nutmeg plants and seeds are shown in
Figure 1.
In this paper, the research results of extracting nutmeg oil are presented using a new method is SCFE. Comparative data on the yield, physical and chemical properties of nutmeg oil between the two methods are WSD and SCFE, are presented in the results of this study. SCFE can be used as a solution to increase the productivity of agricultural products, especially nutmeg oil.
4. Discussion
The physical properties of nutmeg oil are indicated by color. The color is related to the chemical content in nutmeg oil. Nutmeg oil extraction with WSD takes 24 hours for one process. Nutmeg oil contains a light fraction that can be extracted with WSD without pressure. The light fraction was produced at an extraction time of 12 hours. Heavy fractions were extracted by WSD using pressure. The light fraction is above the water while the heavy fraction is below the water. After being separated from the water, the two fractions are then mixed [
10]. The color of nutmeg oil extracted using WSD is colorless (clear), while nutmeg oil extracted using SCFE is yellow. The color difference is due to the different compounds extracted using the two methods. The WSD method is for extracting volatile compounds, while SCFE extracts compounds that are soluble in liquid CO
2. The non-volatile compounds in nutmeg are also extracted by CO
2 gas. Non-volatile compounds such as oil, fat and lignin are extracted by CO
2 gas, giving rise to a yellow color.
The WSD and SCFE extraction methods produce nutmeg oil with very significantly different chemical compound compositions. The significant difference is that extraction with WSD contains the main component myristicin (30.30%) while SCFE contains the largest component sabinene (29.94%). This difference is caused by the properties of the two compounds. Myristicin has volatile properties and tends to be polar, while sabinene has volatile and non-polar properties. CO2 gas has non-polar properties so sabinene has better solubility compared to myristicin. Comparison of the results of nutmeg oil characteristics with both methods shows almost the same results and meets the requirements of ISO 3215:1998. Both extraction methods produce nutmeg that meets ISO 3215:1998 including color, odor, density, refractive index, solubility in ethanol, rotation optical residue evaporator and myristicin content (minimum 10%).
The advantages of the SCFE method compared to the WSD method are the yield and extraction time. The yield with the SCFE method is 12%, while the WSD method produces a maximum yield of 11% (
Table 2). The main advantage is that the extraction time is faster, a maximum of 1 hour, while the WSD is 24 hours. The advantage of the SCFE method is that it does not require fuel that produces CO
2 gas. CO
2 gas used for the extraction process in SCFE can be reused by releasing it into CO
2 in the gas phase. This process makes the SCFE method very efficient and environmentally friendly [
33]
. The weakness of the SCFE method is to produce nutmeg oil which requires refining, because it contains non-volatile chemical compounds. Non-essential chemical compounds such as lignin, oil and fat are also extracted in nutmeg oil [
34]. Tabel 3 shows a comparison of yield and extraction time between WSD and SCFE methods. The extraction method with SCFE produces a higher yield than WSD. This method also requires a shorter extraction time. The SCFE extraction method is preferred because of its high efficiency, shorter extraction time and high selectivity [
30,
31].
The SCFE method in this research has not optimized the powder material parameters, pressure, and temperature. Further research that can be carried out is the optimization of various parameters that influence the quality and quantity of nutmeg oil. Important parameters that influence the extraction method with SCFE are CO
2 gas flow rate, pressure, temperature, and extraction time [
35]. The use of co-solvents and the particle size of the raw materials also influence the extraction results [
36].