A Review of New Methods for Extracting Oil from Plants to Enhance the Efficiency and Physicochemical Properties of the Extracted Oils

Abstract

In general, there are three methods for extracting oil from various sources: mechanical, solvent, and pre-press-solvent. Each of these methods has its own advantages and disadvantages, with extraction efficiency depending on key factors such as the extraction technique, the properties of the plant component matrix, and the solvent used. Factors like temperature, pressure, and time also play a role. Researchers have consistently sought to replace or complement these methods to reduce residual oil in products. This study introduces new oil extraction methods that have gained attention in recent years, including the microwave, pulsed electric field, ultrasound, supercritical fluid, enzymatic, ohmic, and combined methods to enhance efficiency. The research demonstrates that these methods increase oil extraction efficiency and bioactive compound extraction from plant sources, resulting in improved oil quality. Most methods also reduce extraction time, offering researchers and industrialists a variety of options for their oil extraction needs. However, the study notes contradictions in the results, such as varying acidity levels in the oil, which may be attributed to raw materials and study conditions. In the end, it was determined that ultrasound, pulsed electric field, and enzyme methods can be used industrially to extract oil from olives, while supercritical fluid can be used to extract oil from certain seeds.

1. Introduction

The use of oilseeds in human food consumption, as well as their utilization for animal feed, pharmaceuticals, soap making, and fuel, has piqued farmers’ interest and garnered government support for their cultivation [1]. Oils play a crucial role in enhancing the taste, aroma, color, and texture of food, while also imparting a sense of satiety and deliciousness. Nutritionally, lipids serve as a rich source of calories, containing approximately twice as much energy as carbohydrates or proteins. Additionally, they provide vital nutrients such as linoleic acid, linolenic acid, and fat-soluble vitamins (A, D, E, and K). The primary lipid classes include free fatty acids, triacylglycerols composed of fatty acids esterified to glycerol, and phosphoglycerates containing fatty acids esterified to glycerol, along with phosphoric acid and organic bases [2]. Edible fats and oils supply essential fatty acids crucial for human health. Linoleic acid (18:2) and linolenic acid (18:3) are two essential fatty acids necessary for fetal growth and development. These fatty acids play a vital role in pregnancy, lactation, and capillary strength, as the human body lacks the necessary enzymes to synthesize them and thus must obtain them from dietary sources [3]. Broadly speaking, there are three traditional extraction methods in the oil processing field, both historically and in modern industry, as illustrated in Figure 1.

(a)

Mechanical Extraction (Press)

Mechanical extraction, specifically pressing, is commonly used on a small scale. There are two types of mechanical oil extraction: hot and cold pressing. In the hot pressing process, the seeds’ flakes are cooked due to the heat generated, resulting in the removal of about 75% or more of the oil in the seed. During this method, the oil content in the flour is around 16%. Cold pressing, on the other hand, is not a new concept, as hydraulic presses have been commonly used for centuries. This method does not produce heat during operation, making it ideal for producing high-quality products like olive oil, where maintaining taste is crucial. Additionally, cold pressing prevents the increase in temperature that leads to protein denaturation. It is important to note that the crushing efficiency can vary slightly based on the process, variety, location, and growth environment. While hot pressing has a higher oil extraction efficiency than cold pressing, the resulting oil quality is lower due to the heat involved [4]. Cold pressed oils, however, retain their natural properties better and are chemical-free, leading to increased demand. Various factors, such as press pressure, spiral press rotational speed, grain moisture, and process temperature, affect the efficiency of oil extraction by cold pressing. The absence of chemicals in this method results in oil and flour free of chemical compounds, making them suitable for both human and animal consumption. The low initial and operational investment costs, a wide range of capacities (from small scale to 100 tons per hour), and the ease of the process are other advantages of cold pressing. The main drawback of oil extraction by pressing is the high amount of residual oil in the meal, sometimes reported up to 10–20% in some sources. Strict control of the humidity and temperature of the raw material is essential during this process to prevent damage to flour proteins [5,6,7].

(b)

Solvent Extraction

Solvent extraction is a method commonly used for oilseeds containing less than 20% oil, particularly in soybean factories, which play a significant role in the oil industry. The residual oil in the meal after extraction using this method is less than 1%. Establishing initial contact between the solvent and the oil in the seeds is time-consuming, making time an important factor in this extraction method. Hexane is typically the solvent used in this process, as it can easily dissolve vegetable oils. This solvent has a suitable boiling temperature and a relatively low latent heat of evaporation, aiding in energy conservation during distillation. Hexane is non-corrosive to metals, neutral to extracted oil, chemically resistant under process conditions, and readily available at a reasonable price. Despite these benefits, its high flammability necessitates the use of specialized equipment in this extraction method. Due to environmental concerns, low-risk solvents like ethanol, isopropanol, and hydrocarbons are sometimes used in place of hexane. Particle size is a crucial factor in solvent extraction, as reducing it increases solvent penetration into the plant material and improves yield. Drawbacks of using solvents include the lengthy extraction process, high solvent consumption, damage to heat-sensitive compounds, and the production of unwanted materials [8,9,10]. Factors that affect the extraction efficiency of this method include the type and composition of the raw material (such as oil and moisture content), pretreatments that impact cell structure and size, the type of solvent and its temperature, and the ratio of solvent to input grain [11,12]. For instance, Rodrigues et al. (2011) and Toda et al. (2016) noted that raising the temperature results in higher oil extraction efficiency and an increase in free fatty acids. This implies that there is a limit to how much the temperature can be raised [13,14].

(c)

Pre-press and solvent method

This extraction method is used for oilseeds with more than 25% oil content (such as sunflower, canola, etc.). In this method, the oil content in the seeds is first reduced to 16–20% using a press. The press cake obtained is then subjected to solvent extraction under specific conditions (temperature of 50 °C for approximately 7 h), where the remaining oil in the press cake is extracted by adding solvent. The amount of oil left in the flour after extraction using this method is less than 0.5% [10,15].

As mentioned, each of the above methods has its own advantages and disadvantages. Generally, the main disadvantage of conventional methods is the lower oil yield with pressing compared to solvent extraction, which can make oil production economically disadvantageous. On the other hand, the use of organic solvents in the other two methods (using solvents and the pre-pressing and solvent method) raises environmental concerns [16]. Therefore, researchers have been working on finding alternative or complementary methods to improve oil extraction efficiency. The aim of this study was to address the lack of a comprehensive analysis of different oil extraction methods, and their advantages and disadvantages, focusing on extraction efficiency and the physicochemical properties of the resulting oil.

2. Using the Microwave Method

Microwaves are non-ionizing electromagnetic waves with a frequency between 300 MHz and 300 GHz. They are located between radio waves and infrared rays in the electromagnetic spectrum, consisting of two oscillating vertical fields: electric and magnetic fields. Normal heating relies on the conduction-displacement phenomenon, resulting in a significant amount of thermal energy being lost to the environment. However, with microwaves, heating occurs in a specific and selective path without heat loss to the environment, similar to heating in a closed system. The principles of heating with microwaves are based on the direct interaction of waves with solvent and polar materials, working through two phenomena: ion transfer and dipole rotation, which typically occur simultaneously [17]. These waves cause water evaporation from the structure of plant material, increasing pressure in the internal environment. This can lead to material decomposition, membrane rupture, improved efficiency of oil extraction through cold pressing, and oil passage through cell membranes [18].The microwave extraction method is a superior alternative to traditional solid–liquid extraction methods for extracting metabolites from plants. Its advantages over traditional methods include (1) significant reduction in extraction time (usually less than 30 min); (2) decreased solvent usage; (3) enhanced extraction efficiency; (4) automatic device adjustment for accuracy; (5) suitability for heat-sensitive components; (6) ability to extract trace components like heavy metals and pesticide residues from small plant samples; and (7) creation of turbulence during extraction to improve mass transfer. One drawback of this method is its low efficiency when target compounds or solvents are non-polar or volatile [19,20]. On the other hand, due to its thermal nature, this method is unsuitable for the extraction of polyunsaturated fatty acids (PUFAs), as PUFAs are susceptible to oxidation and degradation. In addition, the formation of free radicals and heat during this process is also a disadvantage. Some of these drawbacks can be avoided by using temperature-controlled microwave reactors. However, such reactors are expensive for large-scale processing [21]. In a study conducted by Gallego-Schmid et al. (2018) to assess the environmental impact of microwaves and European legislation on energy efficiency and waste management, it was found that this process reduces the carbon footprint by 4–9%. However, there is still limited information on the environmental impact of this method [22]. The variables of this process play a crucial role in optimizing oil yield. The main variables in microwave-assisted extraction include the solid-to-liquid ratio, microwave power and time (W), and the temperature used [23]. Economic studies on oil processing using microwaves are scarce, but studies on the economic viability of this method in other food processing areas exist. For example, Nguyen and Zhang (2020) demonstrated that using microwaves to extract protein from lobster shells resulted in a 2.7-year return on initial investment, indicating the high efficiency and profitability of the process [24].

Microwaves are utilized for industrial, scientific, medical, and communication purposes. In most countries, four frequencies (915, 2450, 5800, and 22,125 MHz) have been allocated for industrial, research, and medical applications. Unlike X-rays and gamma rays, microwaves are unable to break chemical bonds or damage food molecules due to their low frequency [25]. The use of microwaves reduces the oil extraction time and energy consumption. Consequently, numerous studies have explored the use of microwaves in oil extraction, some of which are briefly summarized in

Table 1. Studies conducted in the field of oil extraction using microwaves.

NO	Raw Material	Study Conditions	Results	References
1	Lingzhi	Comparison of Soxhlet method with microwave-assisted extraction using hexane as the solvent.	Microwave extraction has lower efficiency and greater oxidative stability compared to Soxhlet extraction due to shorter extraction times.	[26]
2	Dragon fruit seed	In a response surface design, various microwave power levels and durations are utilized.	By increasing the time and power of the microwave during oil extraction, the efficiency can be improved. However, it is important to note that the amount of antioxidant capacity initially increases and then decreases with the increase in time and power of the microwave.	[30]
3	Rapeseed	Use of different microwave times	Due to the rupture of the cell membrane, extraction efficiency increases with microwaves use. The oil appears darker in color, and the smell of oxidation intensifies. Additionally, the spiciness and darkness of the oil increase with longer microwave exposure.	[31]
4	Soybean	Using different microwave power and times	Reduction in extraction time from 240 to 60 min	[32]
5	Rice bran	Using a microwave and different solvents such as ethanol and d-limonene.	Increasing extraction efficiency when using microwave and d-limonene solvent can help to increase the concentration of micronutrient compounds in oil.	[33]
6	Palm	Using different microwave power and times	Break the cellular structure of the mesocarp to enhance the extraction of oil and intensify the caramel-like and sweet aroma of the oil.	[34]
7	Hempseed	Power (300, 450 and 600 W) and microwave time (5, 10, and 15 min)	Increase in phenolic compounds and tocopherols is observed in the extracted oil when using microwave compared to the Soxhlet method.	[35]
8	Peanut	Using different microwave times and then extracting the oil with a press	Increasing the microwave time increases the extraction efficiency, acidity, and oil peroxide levels. It also results in higher levels of phytosterols and tocopherols when using microwaves.	[36]
9	Pongamia pinnata seeds	Using different microwave power	Increasing oil extraction efficiency by increasing microwave power	[37]
10	Black cumin seeds	Microwave pretreatment involved varying process times and powers. The seed oil was then extracted using a screw press at different rotational speed.	By increasing the microwave power and processing time, the efficiency of the extraction process increased, leading to higher acidity and peroxide index of the oil. However, this also resulted in a decrease in the oxidative stability of the oil.	[38]

. As shown in this table, the study by Senphan et al. (2024) reported a decrease in extraction efficiency when using microwaves. This decrease is attributed to the significantly shorter processing time of this method [26]. Additionally, when the process time is equal, the extraction efficiency with microwaves is higher. Some researchers have reported that the use of microwaves during oil extraction leads to a decrease in polyunsaturated fatty acids (PUFAs) [27,28]. These researchers stated that the use of microwaves leads to the destruction of PUFAs. On the other hand, some studies indicated that the use of microwaves leads to an increase in tocopherols (vitamin E) due to a decrease in the reaction between these compounds with various polysaccharides, proteins, and peptides present in oilseeds, and the greater penetration of these compounds into the oil [27,29].

3. Pulsed Electric Field

The pulsed electric field process, as a non-thermal method, has been widely utilized to optimize energy consumption and maintain the quality characteristics of products. In recent years, this method has found applications on an industrial scale in biotechnology, pharmaceuticals, manufacturing stimulating lasers, and cleaning metals and polymer materials, as well as in the preparation and processing of food such as fruit extracts, milk, and liquid eggs. This process involves applying pulses in a short period of time (in the range of microseconds), in a strong electric field, to the food material between two electrodes at room temperature. Alternating electric fields with high intensity causes electrical disintegration of cells and increases their permeability [39,40]. The reason for using this process can be attributed to research conducted in Germany. In 1960, Deon Speck described the equipment and various methods of this process for sausage processing; subsequently, with the help of other German researchers, studies were conducted over many years to further develop this process [41]. By utilizing pulsed electric fields, the efficiency of oil extraction increases due to the increase in cell permeability. The most widely accepted theory of how the PEF method works is consistent with the electromechanical model introduced by Zimmerman et al. in 1974. This model explains that the cell membrane is like a capacitor with a low dielectric constant and contains positive and negative ions in the normal state. The integration of these ions on both sides of the membrane leads to a potential difference of about 10 mV in the cell. If this cell is placed in an external electric field, the ions move along the electric field. The movement of ions increases the potential difference until its value reaches a critical limit, which varies in different cells. This critical value depends on the size and shape of the cell, usually ranging within 1–2 kV/cm for plant cells and 10–14 kV/cm for animal cells. When the potential difference reaches a critical level, the attractive force between charges with opposite poles causes electromechanical forces to dominate, leading to the elastic membrane being damaged. This process results in the formation of pores in the membrane, known as electrical permeability or electroporation [42,43,44]. Many researchers have studied the effect of pulsed electric fields as a pretreatment during mechanical pressing, and their reports have indicated a positive impact on the qualitative and sensory properties of the oil obtained [44,45].

To utilize pulsed electric fields in the food industry, specific equipment is required, such as a high voltage pulse generator, process chamber, process control and display system, and cooling system. High-voltage generators are often used in this process to produce alternating currents that result in the destruction of biological cells. These generators transform normal voltages into high-intensity voltages. A power supply is utilized to charge capacitors that store a significant amount of energy, with a key designed to discharge electrical energy from capacitors into the food [46]. The advantages of this method over conventional extraction methods include increased extraction efficiency of bioactive compounds, reduced extraction time and nutrient damage, decreased waste and energy generation, and environmental friendliness [47,48]. The disadvantages of this method include the formation of bubbles during treatment, which can lead to operational problems and non-uniform treatment. Additionally, commercial PEF units are not widely available in many regions around the world [47,49]. Factors affecting the efficiency of electric field extraction include product factors (such as chemical composition, product temperature, and electrical conductivity) and process parameters including electric field strength, number of pulses, pulse frequency, pulse waveform, pulse width, type of chamber, flow conditions, and flow rate [47]. A study titled “Challenges and Opportunities for Pilot Scaling-Up Extraction of Olive Oil Assisted by Pulsed Electric Fields: Process, Product, and Economic Evaluation” showed that the use of PEF in olive oil production reduced the malaxation step by 33%, without affecting the main characteristics of the olive oil. It also increased the oil extraction efficiency by 12.3% and raised the net profit by 36.8%. The study concluded that for small-scale production, the significant initial investment required for PEF equipment may be a challenge in terms of return on investment. However, given the seasonal nature of olive oil production, in medium-to-large-scale production, investing in PEF is a viable option. With an equipment cost of EUR 450,000 and a production output of 5 tons per hour, an annual return of 20% is possible [50].

Table 2. Studies conducted in the field of oil extraction using pulsed electric fields.

NO	Raw Material	Study Conditions	Results	References
1	Peony Seeds	The impact of varying voltages and strengths of the pulsed electric field on the extraction efficiency and tocopherol content of the extracted oil.	Increasing the extraction efficiency of tocopherols compared to the conventional method did not have a significant effect on efficiency with changes in voltage.	[52]
2	Nannochloropsis salina Microalgae	In oil extraction, electric field intensity, power, and various pulse durations of electric field are utilized.	Increasing oil extraction efficiency is achieved through cell destruction and increased membrane permeability.	[53]
3	Rapeseed	By utilizing the strength of the electric field and varying the number of pulses, oil can be extracted using a cold press method	By increasing the intensity of the electric field and the number of pulses, the amount of phenolic compounds and the oxidative stability of the oil increased. The highest extraction efficiency was achieved with an intensity of 4 kV/cm and 80 pulses.	[54]
4	Olive	Industrial oil extraction using a pulsed electric field with a voltage of 24 kV, a pulse width of 6 microseconds, and square pulses.	Increase in extractive oil, phenolic compounds, and bitter taste caused by oleuropein without any noticeable changes in oil oxidation parameters.	[55]
5	Olive Pastes	The voltage and current were 16 kV and 145 amps, respectively. A pump moves the olive paste at a speed of 2300 kg/h, resulting in an average time of 0.19 s spent in the pulsed electric field chamber.	Increasing the extraction efficiency of oil and total phenol	[56]
6	Cannabis seeds	Using different intensities of the pulsed electric field as well as different speeds of the screw press	Increasing the efficiency of oil extraction up to the intensity of the electric field 3 kV/cm, and then decreasing it.	[57]
7	Black cumin seeds	After applying three levels of electric field intensity and three levels of pulse number as pretreatments, the seed oil was extracted using a spiral press at various speeds	By increasing the intensity of the electric field and the number of pulses, the color index of the oil increased, but the oxidative stability decreased. However, they did not affect the refractive index. Initially, increasing the intensity of the electric field and the number of pulses resulted in higher oil removal efficiency and total phenolic compounds. Yet, as these variables continued to increase, both parameters eventually decreased.	[38]
8	Sunflower	Various parameters, such as electric field intensity, device frequency, pulse width, treatment time, and the amount of solvent, can all impact the extraction efficiency.	Increasing oil extraction efficiency using pulsed electric field.	[58]
9	Sesame	The effect of pulsed electric field treatments with different output energies (40 and 240 kJ/kg)	With the increase in the output energy of the high voltage process, the degradability index also increased. These two processes led to an increase in oil removal efficiency.	[59]

lists some studies on the application of pulsed electric fields in oil extraction. Studies have shown that using a pulsed electric field during oil extraction results in an increase in tocopherols, particularly alpha-tocopherols. This is attributed to the low temperature of the process and the enhanced release of these compounds into the oil [51,52]. Conversely, it has been demonstrated that unsaturated fatty acids, specifically oleic acid, are impacted by the pulsed electric field, leading to a reduction in their levels. However, the levels of other fatty acids remain unaffected by the pulsed electric field [29,51].

4. Use of Ultrasound Waves in Oil Extraction

Ultrasound is a mechanical wave that requires an elastic medium and consists of sound waves with various frequencies to disperse. Sounds fall within the frequency range of human hearing (16 Hz to 20–16 kHz), while ultrasound waves have frequencies higher than human hearing but lower than microwave frequencies (20 kHz to 10 MHz). Ultrasound waves with a frequency of less than 100 kHz and a power greater than one watt per square centimeter are known as power ultrasound waves. These waves are extensively utilized in the food industry for various processes such as cutting, degassing, filtration, drying, homogenization, meat crisping, egg quality determination, emulsion formation, surface cleaning, equipment sterilization, fat crystallization, acceleration of oxidation reactions, inhibition of enzyme and microbial activity, and extraction of aroma and taste compounds. Furthermore, acoustic technologies are employed in food evaluation (crispness, firmness, and texture), determination of physical properties (size, shape, volume, and moisture), and grading and separation of food [60,61]. The primary mechanism of ultrasound extraction is associated with cavitation. When liquid is sonicated, the sound waves create cycles of compression and low pressure, leading to the cavitation phenomenon. This intense mixing of solvent particles facilitates solid extraction. The bubbles formed during cavitation cause microcirculation and collision of particles, enhancing internal and eddy diffusion [61,62,63].

The advantages of ultrasound extraction include increased extraction speed and efficiency, reduced processing time, enhanced yield, low solvent consumption, compatibility with various solvents, broad applicability to different plants, improved quality of extracted materials (especially in terms of antioxidant properties), reduced temperature requirements, and the ability to extract heat-sensitive compounds at a low operational cost. However, drawbacks include wave weakening in the presence of a dispersed phase, the need for filtration and separation of the extract from the plant material, limited active ultrasound range within the extractor, potential corrosion of equipment over time, and potential destruction of compounds at high intensities and prolonged exposure to ultrasound [64,65].

Key factors influencing oil extraction via ultrasound include the nature of the sample, sample and solvent matrix, temperature, time, solvent-to-sample ratio, type of solvent, solvent viscosity, solvent vapor pressure, and ultrasonic power [64,66]. Considering the non-polarity of oily compounds, the highest oil extraction performance is achieved using non-polar solvents. The greater the polarity percentage of a solvent, the lower the extraction efficiency. Hexane and petroleum ether, both non-polar solvents, have the most significant impact on increasing oil extraction efficiency. These solvents exhibit only weak van der Waals forces of attraction between particles, resulting in their low boiling points and volatility. A key feature of this method that makes it a green process is that its use reduces the consumption of oxidizing chemicals, mineral acids, iron salts, and other compounds during various processes [67]. Due to the reduced time and energy, as well as the improved oil extraction efficiency, this method is a good candidate for industrializing oil extraction from vegetable seeds [68]. In an analysis presented by Grillo et al. (2022) to calculate the economic cost of olive oil extraction using a combined ultrasound and pulsed electric field method, it was found that the unit costs and energy consumption of both conventional and ultrasonic processes for industrial-scale operations did not exhibit any significant differences in total costs and energy consumption for start-up. However, the ultrasonic process eliminates the need to add water during the separation of olive pulp in the counter, resulting in less olive mill wastewater being produced compared to the conventional method. Water savings of 0.21 L per kilogram of treated olive paste are achieved, significantly reducing waste treatment costs for the entire oil production chain. Additionally, this method requires less space for the installation of large malaxons [69]. Non-polar solute particles are only influenced by van der Waals forces, allowing for the formation of a solution. Therefore, all particles in the solution are affected by this force, facilitating solution formation [10,70,71].

A study investigating the extraction of pomegranate seed oil using ultrasonic waves examined the impact of various solvents on extraction efficiency. The highest efficiency was observed with petroleum ether solvent, followed by hexane, ethyl acetate, diethyl ether, acetone, and isopropanol solvents [72]. Another study conducted on the extraction of safrole oil using ultrasonic waves found that n-hexane had the greatest effect on increasing oil extraction performance, followed by ethyl acetate, petroleum ether, and ethanol [73]. The use of mixed solvents enhances the productivity of suitable oil compounds in ultrasonic extraction [74]. Additionally, increasing the ratio of solvent to sample enhances the efficiency of oil extraction. At high solvent ratios, the reduction in solution viscosity promotes the diffusion of the solvent into the sample tissue, leading to an increase in solvent concentration towards the sample matrix and ultimately enhancing extraction performance [64,75]. Other influential factors in extracting oil from oilseeds using ultrasonic waves include extraction time, process temperature, and ultrasonic wave power. With increased extraction time, the cell wall is disrupted due to the energy generated by the cavitation phenomenon, facilitating the penetration of oily compounds into the solvent. However, as extraction time continues to increase, the concentration of oily compounds in the cell tissue and the solvent reaches equilibrium, resulting in a decrease in the release and penetration of these compounds into the solvent and a subsequent decrease in extraction performance. As the temperature rises, the number of cavitation-induced bubbles also increases, reducing the surface tension and viscosity of the solvent. This decrease in viscosity allows the solvent to more easily penetrate the cell tissue, thereby increasing extraction performance through enhanced mass transfer. The power of ultrasound affects the cavitation phenomenon. As the power of ultrasound waves increases, the temperature of the process also increases. By keeping the process time constant, the viscosity and surface tension of the solvent decrease and the vapor pressure increases. At higher temperatures, the cavitation threshold is lowered and bubble formation is better, ultimately increasing the extraction performance [72,73,76]. In

Table 3. Studies conducted in the field of oil extraction using ultrasound.

NO	Raw Material	Study Conditions	Results	References
1	Nigella sativa seed	Using different ultrasound temperatures and times and comparing ultrasound with the conventional method and supercritical fluid	The efficiency of oil extraction increases with longer ultrasound exposure and higher temperatures. Ultrasound extraction shows higher efficiency compared to supercritical fluid extraction, with no significant difference in efficiency compared to the Soxhlet method. However, oil extracted using the ultrasound method exhibits higher antioxidant activity than oils extracted using the other two methods.	[79]
2	Blackberry Seed	Using time, temperature, and different intensities of ultrasound waves	Improving oil extraction efficiency and bioactive compound retention using ultrasound.	[80]
3	Apple seeds	The impact of time and ultrasonic power on the extraction process will be examined, along with a comparison to the supercritical fluid method	Increasing ultrasonic power and time can enhance efficiency. Additionally, increasing oil acidity through longer ultrasonic treatment does not result in a significant difference in extraction efficiency when compared to conventional and supercritical fluid methods. However, the ultrasonic method does offer a shorter extraction time in comparison to these two traditional methods.	[81]
4	Hempseed	Using different amplitudes and times of ultrasound	Increasing antioxidant capacity and oil extraction efficiency	[82]
5	Rice bran	The use of ultrasound in oil extraction and its comparison with the conventional method	There was no significant change in the amount of gamma oryzanol and oil extraction efficiency in the two methods mentioned, despite a reduction in extraction time when using ultrasound.	[83]
6	Olive	Evaluating the effects of installing and operating a high-power ultrasonic device for oil extraction with a frequency of 20 kHz, capable of working with a capacity of 3200 kg/h	The results showed that high-power ultrasound did not have a significant effect on the quality parameters of olive oil (acidity, peroxide, and spectrophotometric indices). However, a significant increase in the content of phenolic compounds was generally observed.	[84]
7	Radish seed	Using different temperatures and solvents	By increasing the temperature of the oil extraction process, the efficiency of oil extraction increased. Additionally, the use of ultrasound led to an increase in phenolic compounds and phytosterols.	[85]
8	Nigella sativa seed	Investigating the use of ultrasonic power and time pretreatments on the quantity of phenolic compounds and some physicochemical properties of Nigella sativa seed oil extracted by cold pressing	With the increase in ultrasonic power, the efficiency of oil extraction, acidity, total phenol, peroxide, and color all increased significantly. Similarly, increasing the ultrasound time also led to higher levels of oil extraction, acidity, total phenol, peroxide, and color. Interestingly, using ultrasound as a pretreatment did not have a significant impact on the refractive index of the oils.	[86]
9	Rapeseed flakes	Using alternative solvents to replace hexane in oil extraction processes with the assistance of ultrasound technology	The suitability of isopropanol solvent for oil extraction efficiency is comparable to hexane solvent, while ethanol solvent is not suitable for oil extraction.	[87]
10	Sunflower	The variables of this study included different frequencies of ultrasound, type of sample (with and without skin), and process time	Improving the extraction efficiency of oil and alpha-linolenic fatty acid, as well as reducing peroxide levels, through the use of ultrasound.	[77]

, some studies that have used ultrasound in oil extraction are provided. Studies have shown that polyunsaturated fatty acids, such as linoleic acid (18:2 n-6c), γ-linolenic acid (18:3 n-6), and α-linolenic acid (18:3 n-3), are increased when ultrasound is used in the extraction of oil from flaxseed [68]. However, in more stable oils like sunflower oil, the use of this process does not significantly affect the amount of fatty acids [77]. A study conducted to investigate the effect of ultrasound on virgin olive oil showed that the use of ultrasound did not significantly affect the nutritional composition of this oil, including phenols and tocopherols [78].

5. Use of Supercritical Fluid in Oil Extraction

Supercritical fluid is a substance that is placed at temperatures and pressures above the critical point. In this condition, the substance is not a gas or a liquid, but an intermediate state between the two, combining the permeability properties of gases and the dissolution power of liquids. The solubility of substances in this phase changes with density, controlled by temperature and pressure. After the desired substance penetrates the phase, at the end of extraction, by adjusting temperature and pressure, the supercritical phase can be removed as a gas, leaving behind the extract without solvent [88]. In this method, the choice of solvent is crucial. Carbon dioxide is commonly used for extracting non-polar compounds like hydrocarbons due to its affordability, low toxicity, low flammability, selectivity, potential for extracting heat-sensitive compounds, and favorable critical conditions (temperature 304 degrees Kelvin and pressure 7.3 MPa) [89].

The moisture content of the plant material is significant in this method. Water in the plant material can freeze, creating a physical barrier against the supercritical liquid. Additionally, the ice can partially enter the supercritical phase, leading to the dissolution of unwanted compounds. The particle size of the samples also affects extraction efficiency, similar to other methods. Increasing the flow rate of carbon dioxide only reduces extraction time, without significantly increasing the yield [89,90]. Advantages of this method over conventional extraction methods include high extraction speed, low or no organic solvent, no solvent residue, preservation of heat-sensitive compounds, tunability of solvent density resulting in selective extraction of compounds, and, ultimately, low operating costs. Disadvantages of this method include high startup costs, a need for technical knowledge, and considerations of the solvent used (e.g., phase behavior, cross-linking zone) [91]. While the production of CO₂ in this method is harmful to the environment, the use of CO₂ as an extraction solvent is a key feature that allows this method to contribute to the circular economy cycle. For instance, to mitigate CO₂ emissions, technologies such as carbon capture and storage (CCS) and carbon capture and utilization (CCU) are being developed. CCS involves capturing emitted CO₂, compressing it, and injecting it into deep geological, oceanic, or mining sites. In contrast, CCU enables the recovery and reuse of captured CO₂ rather than simply storing it. Therefore, incorporating CO₂ into the development of products and services can help reduce global greenhouse gas emissions. This approach allows for the direct capture of CO₂ from industrial off-gases or even from the atmosphere. In this context, supercritical fluid systems can utilize CO₂ from these technologies to recover valuable compounds while simultaneously removing CO₂ from the atmosphere and reducing the carbon footprint. Thus, extraction aligns with the principles of the circular economy [92]. There are currently over 200 commercial supercritical fluid extraction plants worldwide, many of which are used to extract natural compounds from plant products [93]. Numerous techno-economic feasibility studies have been conducted on this method for extracting natural products, detailing the production costs of various essential oils [94]. In a study by Chañi-Paucar et al. (2021), economic calculations regarding the extraction of oil from Baru seeds using this method revealed that the operational cost per kilogram of oil from the seed ranges from USD 87 to USD 118. When subtracting this cost from the price of the seed (considering its oil percentage of 22–29%) and the price of its oil-free meal, it was determined that this method is cost-effective for extracting this specific oil. However, given these prices and the lower prices of conventional oils (such as soybean and rapeseed), it appears that this method is not currently a suitable option for extracting conventional oils, except for specific oils [95].

Table 4. Studies conducted in the field of oil extraction using supercritical fluid.

NO	Raw Material	Study Conditions	Results	References
1	Black cumin seed	Comparison of supercritical fluid method with cold press method and extraction with solvent	The oil extracted using supercritical fluid showed higher efficiency and contained higher levels of phenolic and tocopherol compounds compared to the other two methods.	[96]
2	Moringa oleifera Seed	The effects of temperature, time, and pressure, three effective features in extraction, on the efficiency of Moringa seed oil extraction using response surface methodology and single factor test	The ideal conditions for extracting oil using supercritical fluid from moringa seeds are as follows: an extraction temperature of 45 degrees Celsius, an extraction time of 2.5 h, an extraction pressure of 50 MPa, and a carbon dioxide flow rate of 240 L per hour.	[99]
3	Canola seeds	Using response surface methodology to optimize oil extraction conditions from canola seeds with the highest concentration of bioactive compounds	The oil extracted using supercritical fluid under optimal conditions contained eight times more tocopherol than the conventional method. Additionally, there was no change in the fatty acid structure of the samples.	[100]
4	Pinus gerardiana	Comparison of oil extraction with supercritical fluid by Soxhlet method	Although the extraction efficiency with supercritical fluid was lower than the Soxhlet method, the time and temperature required for this process were also lower.	[101]
5	Olive cake	Investigating the effects of temperature, time and supercritical fluid pressure on oil extraction using response surface methodology	The use of supercritical fluid has resulted in reduced process time and temperature. However, this method has also led to an increase in the bioactive compounds of the oil.	[102]
6	Actinostemma lobatum Maxim. kernel	Comparison of three methods of supercritical fluid extraction, cold press and Soxhlet in oil extraction	There is no significant difference in the amounts of tocopherol and plant sterols in the oil obtained from three different extraction methods. However, the extraction efficiency was higher in the supercritical fluid method.	[97]
7	Chañar almond	Oil extraction under the influence of different temperatures and pressures of the supercritical fluid device	The optimal conditions for chañar almond oil recovery were at 60 °C and 40 MPa, resulting in a 40 ± 1% oil yield. Under these conditions, the highest levels of monounsaturated and polyunsaturated fatty acids could be recovered.	[98]
8	Rapeseed	The effect of pressure, temperature, and supercritical fluid extraction time parameters	Reducing the time of the oil extraction process. As time and pressure increased, so did the extraction efficiency.	[103]

presents the effects of supercritical fluid on various properties of oils extracted from different products. As shown in this table, utilizing this method results in an elevation of low-level compounds such as phenolic compounds and tocopherols in the oil [96,97]. Conversely, through the optimization of this process, the oil can attain the highest levels of monounsaturated and polyunsaturated fatty acids [98].

6. Enzymatic Extraction

Enzyme-assisted extraction is considered an alternative to conventional techniques for extracting valuable compounds using water as a solvent instead of an organic solvent. To extract lipid reserves stored in cells, it must be possible to cross several barriers: first, the extra cell walls (or secondary cell walls), then the cell wall, and finally the oleosomes. Each cell wall has its own components, which are sometimes organized into a complex structure and are naturally synthesized and broken down by specific enzymes. For example, the secondary cell wall of rapeseed is composed of 39% pectin, 29% hemicellulose, 22% cellulose, and 8% arabinogalactans, and constitutes 20% to 28% of the whole grain. The primary cell wall contains 10% glycoprotein, which is very rich in hydroxyproline; it was originally called extensin, but is now called HRGP (hydroxyproline-rich glycoprotein) [104]. Enzymes such as pectinase, β-gluconase, β-glucosidase, cellulase, and xylanase degrade the polysaccharides of the cell wall and thus release the related compounds. This technique is mainly used when phytochemicals are dispersed in the cell cytoplasm and hydrophobic or hydrogen bonds are present in the matrix, which makes it difficult to extract bioactive compounds by traditional techniques. Apart from that, the biological origin, environmentally friendly nature, and higher extraction efficiency of this method have increased the demand of this method [105]. However, since this method takes longer and is more expensive, and separating emulsion and drying protein and meal can be challenging, it is rarely used [106]. On the other hand, this method has the ability to separate oil and protein simultaneously, and also removes the gumming step from oil extraction [107]. Enzyme-assisted extraction offers advantages such as high efficiency and mild conditions, while ensuring the preservation of extraction properties and stability [108]. This method is also considered one of the green processing methods compared to traditional extraction methods. The type of enzyme, the dosage and conditions required by the enzymes, the process time and temperature, the properties of the plant material such as particle size, water content, and chemical composition, and the solvent-to-solid ratio are all factors that affect the rate of enzyme-assisted extraction [109]. In a study conducted by Cheng et al. (2019) on the operating cost of oil extraction from soybeans, it was found that this method is an innovative process for oil extraction. However, operational costs remain the main issue preventing the use of this method on an industrial scale, accounting for only 27% of total revenue [110]. However, it seems that using this method for olive oil extraction is economically viable due to the different extraction method [111]. In

Table 5. Studies conducted in the field of oil extraction using enzymatic extraction.

NO	Raw Material	Study Conditions	Results	References
1	Camellia oleifera seed	Using different enzymes to extract oil	The use of alpha-amylase and protease enzymes resulted in improved oil extraction efficiency.	[112]
2	Hodgsonia heteroclita oilseeds	The use of different commercial enzymes as a pretreatment of the oil extraction process with a press	The incubation time for these enzymes on this seed was approximately 76 min. The oil extracted with enzyme pretreatment contained more gamma tocopherol than when extracted using other methods.	[113]
3	Walnuts	Comparison of enzyme-assisted extraction with hexane solvent	The oil obtained from enzyme pretreatment had higher oxidative stability and tocopherol content compared to the oil obtained from the solvent.	[114]
4	Sesame	Comparison of enzyme extraction method with press and solvent methods	The use of enzymes in extracting oil results in a higher antioxidant capacity and phytosterols. Overall, the quality of sesame oil is improved with this method.	[115]
5	Apricot kernels	Enzymes are used in various concentrations	Improving the efficiency of oil extraction by using enzymes separately and in combination, without significantly affecting the chemical properties of the oil.	[116]
6	Melon seed	Examining different conditions of enzyme type, pH level, temperature, and incubation time on oil extraction	The most important factor in extracting oil from melon seeds with the help of enzymes was the incubation time. The optimization process in this study included maintaining a pH of 7, an incubation time of 31 h, and a temperature of 58 °C.	[117]
7	Olive	The effect of olive variety and enzyme concentration on the physicochemical properties of the extracted oil.	The use of enzymes led to an increase in extraction efficiency and phenolic compounds, but it also reduced the amount of oil turbidity. However, enzymes did not have a significant effect on the amount of iodine index and acidity.	[118]
8	Corn germ	Using different enzymes and comparing them with extraction with hexane solvent	By increasing the efficiency of extraction using enzymes, as well as ensuring that there are no significant changes in the composition of the resulting oil in both extraction methods.	[119]

, the effect of extraction with the help of enzymes on some properties of extracted oils from different sources is given. Enzyme-assisted oil extraction is considered an extraction method based on the concepts of “green chemistry” and “green engineering”. The extracted oil has superior physicochemical parameters and nutrients, such as tocopherols, squalene, and polyunsaturated fatty acids, compared to pressing and solvent methods [107].

7. Ohmic Extraction Method

In recent years, heating techniques have undergone significant improvements. Some notable methods include resistance heating, dielectric heating (such as microwave and radio frequency heating), and induction heating. In all of these methods, heat is generated within the food itself, leading to increased efficiency [120]. The resistance heating method, also known as Joule heating, is a volumetric heating method where the food material acts as a resistor, generating heat when an electric current passes through it [121]. Due to its numerous advantages, resistance heating can be seen as an alternative to traditional methods. Its speed and short heating time, along with energy savings, help preserve the quality of the final product [122]. Other advantages of this method include reduced maintenance costs (due to the absence of moving parts), reduced risk of sedimentation during heat transfer, immediate shutdown of the system, and environmental friendliness. Disadvantages of this method include the lack of general information, the need to constantly adjust the device according to the variable properties of plant compounds, monitoring and control of the process, and the complexity of the temperature gradient between the products [123]. This process uses electricity instead of thermal energy obtained directly from the combustion of fossil fuels and can play a key role in the transition to a decarbonized industry, and thus does not have a significant impact on the environment [124]. The electrical conductivity of the food compounds, the current intensity, voltage, and frequency used, and the shape and dimensions of the food are factors that affect the extraction efficiency of this method [125]. The efficiency and speed of extraction are enhanced in this process by the rupture of plant cells caused by the current passing through them. This shortened process time also prevents the extraction of heavy compounds [126]. Several researchers have investigated industrial applications of ohmic heating, including aseptic processing, sterilization, pasteurization, drying, and distillation. However, oil extraction using this method has been less studied.

Table 6. Studies conducted in the field of oil extraction using ohmic extraction.

NO	Raw Material	Study Conditions	Results	References
1	Mustard	Investigating the effect of electric field intensities and different times of ohmic process as pretreatment on oil extraction and some of its chemical properties	It was found that the ohmic process increased the efficiency of oil extraction. However, an excessive increase in the time and intensity of the electric field led to an increase in the acidity and peroxide levels of the oil.	[128]
2	Rice Bran	Investigating voltages, temperatures and different times of the ohmic process in oil extraction	By using this process, the beneficial compounds in the oil increased, as well as its shelf life, but the acidity of the rice oil decreased.	[129]
3	Hemp	Optimization of hemp oil extraction parameters is being conducted to determine the impact of voltages and varying durations of the ohmic process. The goal is to enhance oil extraction efficiency, increase antioxidant activity, and decrease the color and peroxide index of the oil	The optimal extraction conditions were determined to be a solvent ratio of approximately 73% hexane to 27% isopropanol (v/v%), a process time of 8.40 min, and a voltage of 51.61 V/cm. Ultimately, ohmic heating was proven to be a simple and efficient method to enhance oil extraction	[130]
4	Tomato Seed	The impact of ohmic heating parameters, such as electric field strength, end point temperature, and storage time, on the oil extraction process was studied using the box-Banken.	A 10% increase in the oil compared to the control sample resulted in all physicochemical quality parameters falling within the acceptable range defined by international standards for edible oils. These parameters include refractive index, color, specific gravity, free fatty acids, saponification value, peroxide value, and iodine index.	[131]
5	Gac aril	Comparison of conventional method with ohmic method in oil extraction	The extraction efficiency of oil, beta-carotene, and lycopene increased due to greater destruction of the plant cell wall.	[132]
6	Sesame seeds	The effect of ohmic heating parameters (electric field strength, end point temperature, and storage time) on the oil extraction process was investigated using a factorial design	The maximum oil extraction of 43.15% was achieved when the sample was exposed to a temperature of 85 °C with an electric field strength of 900 V/m for 10 min. The FFA values obtained in this study were lower than the maximum limit in all treatments used. However, the use of ohmic heating led to an increase in free fatty acids	[133]

illustrates the impact of ohmic extraction on various properties of oils extracted from different sources. The effect of ohmic heating on the vitamin and antioxidant content of oils can vary. While this method generally preserves the natural antioxidants found in oils, such as tocopherols, prolonged or excessive heating may result in the loss of these heat-sensitive compounds. However, compared to traditional extraction methods that involve higher temperatures and longer processing times, ohmic heating is generally considered more favorable for preserving the vitamin and antioxidant content of oils. On the other hand, ohmic heating can help preserve phytochemicals and bioactive compounds found in oils, such as phenolic compounds and phytosterols. The gentle and precise heat provided by ohmic heating helps reduce the degradation and loss of these beneficial compounds, preserving their nutritional properties. Studies have shown that oil extracted using this method has higher levels of omega-3 and omega-6 fatty acids than solvent- and press-extraction methods [127].

Figure 2 shows a schematic of the use of pulse electric field, microwave, ultrasound, and ohmic methods in the pretreatment of oil extraction from oilseeds.

8. Oil Extraction Using Combined Processes

Choosing the right extraction process is crucial for maximizing compounds from tissues. Extraction efficiency is influenced by several critical elements, including the extraction technique, matrix properties of plant components, the solvent used, temperature, pressure, and time [134]. Researchers sometimes opt to combine these methods to capitalize on the simultaneous benefits outlined in this article. This approach results in oil with more bioactive compounds and improved physicochemical properties [135].

Table 7. Studies conducted in the field of oil extraction using combined processes.

NO	Raw Material	Study Conditions	Results	References
1	Sesame	Combining enzyme-assisted treatment and subcritical fluidand then oil extraction with a press	Due to cell hydrolysis by enzymes and improved destruction of the wall through these methods, sesame oil efficiency has significantly increased. Additionally, there has been a notable increase in lignan and phenol content, as well as improved oxidative stability of the oil.	[138]
2	Tomato seed	A combination of ohmic heating and microwave heating as pretreatment	Improving the efficiency of oil extraction and bioactive compound extraction, increasing the levels of oleic acid and linoleic acid, and reducing energy consumption. This is achieved by decreasing process time and solvent usage compared to traditional methods.	[139]
3	Sunflower seeds	Using microwave pretreatment with different process times (0 to 120 S) and then ultrasound with three different time levels (0 to 50 min) and oil extraction with a screw press.	Improving the efficiency of oil extraction can enhance the acidity, color index, and quantity of unsaturated fatty acids in the oil, such as linoleic acid.	[136]
4	Niger seed	Microwave irradiation times (0–200 s) and pulsed electric fields (PEF) intensities (0–5 kV/cm) as pretreatments	There was a decrease in unsaturated fatty acids and an increase in saturated fatty acids (p < 0.05). Additionally, there was an increase in alpha-tocopherol and oil extraction efficiency when using combined pretreatment before oil extraction by pressing.	[137]
5	Canola seeds	Microwave irradiation times (0–200 s) and pulsed electric fields (PEF) intensities (0–5 kV/cm) as pretreatments	Increasing the extraction efficiency of oil and phenolic compounds while not affecting the refractive index of the oil, and also increasing the oil peroxide level.	[140]
6	Jatropha curcas L. seed	A combination of ultrasonication and aqueous enzymatic	Reducing the extraction process time and increasing oil extraction efficiency.	[141]

provides examples of studies that have utilized a combined method for oil extraction. As shown in this table, utilizing combined processes can increase the levels of bioactive compounds and unsaturated fatty acids, depending on the specific type of process [136,137].

9. General Conclusions

This study aimed to introduce new methods of oil extraction from various plant and animal sources. Recent research in the field has shown the positive impact of these methods on the physicochemical properties of extracted oils, particularly in terms of extraction efficiency and bioactive compounds. On the other hand, studies have shown that certain methods such as ultrasound, pulsed electric field, and enzyme use have the potential to be industrialized for specific sources like olives. Additionally, almost all of the methods studied for oil extraction did not have a significant impact on environmental pollution levels. Therefore, considering various factors that were discussed in this study, such as increasing oil extraction efficiency, it is hoped that these methods will also be researched and utilized industrially for other oilseeds. However, further comprehensive studies on the use of different extraction methods to determine the best method for extracting oil from specific materials are necessary.