**6. Advances in macadamia oil extraction with green technologies**

The traditional extraction method is cold mechanical pressing, a technology that requires a large energy input and provides a product with fine suspended solids and low efficiencies (35–40% w/w) [55]. An alternative to increasing the efficiency and

#### *Challenges and Advances in the Production of Export-Quality Macadamia and Its Integral Use… DOI: http://dx.doi.org/10.5772/intechopen.105000*

quality of the product would be extraction with organic solvents, but with enormous disadvantages from the energy, nutritional, and environmental point of view [56]. The growing trend in the consumption of healthy, safe, and functional foods has motivated studies on special cold-pressed oils, including macadamia oil. Consumers prefer cold-pressed macadamia nut oil (CPMO) over refined and solvent-extracted oil due to its exceptional quality and safety attributes [1]. In recent years, the technology of liquefied gases and supercritical fluids has gained relevance due to the use of solvents considered "green," since they are nontoxic, safe, and cheap [57]. The use of supercritical CO2 (sc-CO2) for the extraction of various products of interest has gained notoriety [58]; however, for the extraction of oils, it was reported that sc-CO2 requires long extraction times, high temperatures that could degrade antioxidants present in macadamia, and high pressures that have been shown to negatively influence the profile of fatty acids since lower amounts of unsaturated fatty acids are obtained [11, 59–61]. Besides, subcritical CO2 or liquefied CO2 has numerous advantages, such as operating below the critical point, suitability for the separation of thermolabile compounds, avoidance of thermal degradation of components at the time of extraction, and high selectivity to flavor-representative and esterified components [62, 63]. Additionally, it is nonflammable, safe, cheap, odorless, nontoxic, highly available, and environmentally friendly [64]. However, CO2 is a nonpolar molecule, which is why it is related only to compounds of the same nature. However, the addition of a suitable cosolvent can improve the solvent properties of CO2, expanding the range of lipid extraction [59, 65]. Due to the ease of removing ethanol from the oil, its use as cosolvent is allowed in the food industry. It was shown that the lipid extraction range is extended if it is used with CO2; it also decreases the viscosity and surface tension of the oil-CO2 mixture and decreases the electrical permittivity of CO2 and, therefore, the polarizability [59, 65]. As for the critical point of the CO2-ethanol mixture, it increases with the alcohol fraction, a phenomenon that allows the subcritical work zone to be extended [11, 59–61].

Liquefied propane is another permitted cosolvent that has multiple advantages over solvents such as n-hexane (widely used for the extraction of edible oils), since it is cheap and does not leave a toxic residue [66]. The use of light hydrocarbons as cosolvents substantially improves the extraction kinetics due to the good solubility of triglycerides, making the operation faster and more efficient. Regarding the temperature and critical pressure of the CO2-C3H8 mixture, it presents an antagonistic behavior, since as the fraction of C3H8 increases, the critical pressure decreases, while, for low fractions of C3H8, the critical temperature decreases below the critical temperature of pure CO2, but then increases substantially. Low concentrations of C3H8 are said to push the critical temperature of the mixture [67].

A simple method to study the main operating variables that influence solid–liquid extraction with liquefied gases is the high-pressure Soxhlet, whose operation is similar to the conventional Soxhlet used to determine the fat content of a vegetable matrix (**Figure 7**). To create the necessary temperature gradient, the ends of the extractor must be subjected to a temperature difference such that, at the base, the evaporation of the solvent-cosolvent mixture is verified, while at the head, the condensation of these is allowed. This could be achieved by immersing the base of the extractor in a water bath at a controlled temperature and circulating cold water through the condenser, which must be conveniently located so that the film of condensate drips onto the sample contained in the extraction cartridge. The net effect would be the periodic recirculation of CO2 in the extraction vessel, working under liquid–vapor equilibrium conditions. An extraction cycle is considered complete when the condensate in the

#### **Figure 7.**

*High-pressure Soxhlet extraction system: (1) pressure gauge, (2) temperature sensor, (3) adjusting and closing nuts, (4) pressure vessel – Parr reactor, (5) siphon, (6) charge and decompression line, (7) shutoff valve, (8) condenser, (9) extraction cartridge, (10) solvent chamber, and (11) sample chamber. Elaboration: Smidt, M.*

sample chamber is siphoned into the solvent chamber. The number of extraction cycles is determined by recording the temperature in the extraction chamber, where a temperature sensor is inserted at the same level as the siphon tube. The sensor will record a temperature gradient each time the solvent mixture is siphoned into the sample chamber. This process approximates a continuous multistage countercurrent extraction operation [68]. At the end of the extraction time, the container must be slowly depressurized; the solvent mixture will evaporate by sudden decompression (flashing) obtaining, on one side, an exhausted solid in the extraction cartridge and, on the other side, the extracted oil free of solvent in the solvent chamber.

The efficiency on any solid–liquid extraction operation with liquefied gases strongly depends on the proper selection of the solvent and cosolvent, as well as the nature of the solid matrix and the operating conditions [69]. The extraction temperature is an important variable, since it can significantly affect the quality of the product if it is very high and must be established together with the pressure, so that the working conditions are maintained in the subcritical region. Regarding the cosolvent fraction, it is important since the critical point of the mixture changes in relation to that of the pure solvents, so a fraction that allows the mixture to work in the subcritical region should be selected [59]. Respecting the granulometry, the efficiency is governed by this parameter since the components to be extracted must come into contact with the solvent, which will determine the extraction time and which, in turn, influences which components are extracted [70]. Initially, it is the solubility that controls the extraction process, and over time, it is the internal diffusion that governs the extraction process [71].

Experimental tests were conducted with subcritical mixtures of CO2-ethanol and CO2-C3H8, separately, by means of the high-pressure Soxhlet method, with the application of a multilevel factorial design, and the effect of extraction

#### *Challenges and Advances in the Production of Export-Quality Macadamia and Its Integral Use… DOI: http://dx.doi.org/10.5772/intechopen.105000*

temperature, mass fraction of cosolvent, and average granulometry of the dry kernel on the extraction efficiency of *M. integrifolia* nut oil was evaluated. Twenty grams of kernels was used for each experimental condition, and these were subjected to the different conditions according to the experimental planning; previously, the moisture content of the macadamia was adjusted to <1.5%. For the CO2-ethanol case, the extraction time was 6 h, while for the CO2-C3H8 case, it was 1 h. At the end of the extraction time, the extractor was decompressed and the oil obtained was physicochemically characterized. The partially defatted solid was subjected to total lipid analysis to determine, indirectly, the extraction efficiency, as well as the characterization of some parameters of interest for its further use. It should be noted that for the CO2-ethanol mixture, additional vacuum evaporation is required to strip the oil of the cosolvent.

In the case of ethanol-assisted extraction, the highest efficiency (66.5% w/w) was obtained at 45°C, average granulometry 4.05 mm, and 20% (w/w) of cosolvent fraction. On the other hand, the extraction assisted with propane had a maximum efficiency of 72.6% (w/w) at 38°C, average granulometry 4.05 mm, and 45% (w/w) of cosolvent fraction. Both efficiencies are higher than those reported for obtaining macadamia oil by cold mechanical pressing, which is the method mainly applied for the extraction of this oil [72]. **Figure 8** shows the behavior of the extraction efficiency with temperature (X1) and average granulometry (X2) with 20% (w/w) ethanol (**Figure 8a**) and 45% propane (**Figure 8b**). The lowest extraction efficiency with CO2-ethanol required two cycles/h, while the highest required six cycles/h. On the other hand, the lowest extraction efficiency with the CO2-C3H8 mixture required two cycles/h and the highest four cycles/h; these physical phenomena allow us to visually explain the differences between treatments that lead to higher extraction yields.

In edible oils, the recommended physicochemical quality control determinations include acidity index, peroxide index, and iodine value [4], which can be complemented with the saponification index, refractive index, and rancidity, in order to have a bigger picture of oil quality. Based on this, the aforementioned determinations were made for the oil obtained in the treatment with the highest efficiency for each solvent mixture (**Table 2**). The acidity index is low (< 4, **Table 2**), which implies a reduced

#### **Figure 8.**

*M. integrifolia oil extraction efficiency against temperature and average granulometry for subcritical extraction assisted by 20% (w/w) ethanol (a) and 45% (w/w) C3H8 (b).*


#### **Table 2.**

*Physicochemical determinations of M. integrifolia oil quality carried out on the oil obtained in the best treatment of each solvent mixture.*

amount of free fatty acids product of triglyceride degradation reactions that increase the quality of an oil, this complemented by a high oxidative stability verified by the low peroxide index (< 15, **Table 2**) [77], corroborated by a negative test for rancidity. The low iodine value classifies it as a nondrying oil (<100 g I/100 g), which is why a low content of polyunsaturated fatty acid is predicted [74]. Given the high saponification index, its refining is not recommended unless its final destination is the soap industry [72]. These results agree with what was reported by Mereles and Ferro [14], who have characterized freshly extracted macadamia oil from three consecutive harvests.

Regarding the fatty acids present in the extracted oils, these were contrasted with the fatty acid profile of virgin macadamia oil, extracted by the cold mechanical pressing of the raw material itself (**Table 3**). The values are close to each other, with a high and encouraging content of oleic acid as well as palmitoleic acid, both monounsaturated fatty acids of special interest in terms of nutraceutical and skin regenerative benefits [72]. A low content of polyunsaturated fatty acids was found, which is related to the low iodine value reported.

As for the defatted meal from both extraction processes, a high content of protein (> 18% w/w), fiber (>13% w/w), and carbohydrates (> 41% w/w) was verified, which makes it a candidate for the production of protein concentrates, isolated protein for the production of nutritional supplements, and partially defatted flours of interest for celiacs, among others [11, 78].
