**4. Methods for obtaining vegetable oils**

The main anthocyanins found in açaí are cyanidin-3-*O*-glucoside and cyanidin-3-*O*-rutinoside. In bacaba, it is cyanidin-3-glucoside. This information is presented in **Table 3**, as well as an overview of some anthocyanin extraction applications of açaí, bacaba, and other raw

In addition to anthocyanins, other bioactive compounds have been identified in açaí and bacaba. Pacheco-Palencia et al. [50] analyzed two species of açaí and identified several flavones, including homoorientin, orientin, deoxyhexose taxifolin, and isovitexin; flavanol derivatives, including (+)—catechin, (−)—epicatechin, procyanidin dimers and trimers, and phenolic acids such as protocatechuic, p-hydroxybenzoic, vanillic, syringic, and ferulic. Phenolic compounds are also reported to be potentially protective against cardiovascular disease and cancer [51]. Also, large amounts of phenolic compounds such as phenolic acids, flavanols, and flavonols can be found, which act as cofactors to improve the biological action of anthocyanins [52].

**Figure 2.** Chemical structures of the main anthocyanins found in açaí and bacaba (**a**): 2-(3,4-dihydroxyphenyl)-5,7 dihydroxy-3-chromeniumyl6-*O*-(6-deoxy-α-L-mannopyranosyl)-β-D-glucopyranoside; (**b**): 2-(3,4-dihydroxyphenyl)-

5,7-dihydroxy-3-chromeniumyl β-D-glucopyranoside [nomenclatures according to IUPAC].

Santos et al. [53] evaluated the content of bioactive compounds and total antioxidant capacity of native fruits of the Amazon palm trees, including the species *O. bacaba*. Their results showed a high content of total polyphenols, presence of carotenoids, higher levels of anthocyanins, and antioxidant capacity in the bacaba extracts. In the study of Finco et al. [40], the phenolic classes: C-glycoside, flavonoid, C-hexoside, C-glycosylflavone, isorhamnetin hexoside, quercetin hexoside, quercetin diglycoside, quercetin glycoside, and isorhamnetin glycoside, were identified.

materials. Their chemical structures are presented in **Figure 2**.

162 Superfood and Functional Food - An Overview of Their Processing and Utilization

The economic importance that aromatic plants have in the Amazon region is associated with the application of their vegetable oils and use of their aromas in technological and industrial processes. Because of this, there is a greater investment in such plants extraction sector, causing an expansion of the domestic and international markets.

The soil and climate of the Amazon region are conducive to the proliferation of palm trees, among which there are the oleaginous ones cultivated with commercial purpose. This is the case of açaí and bacaba, whose extraction already constitutes a significant economic activity in the state of Pará-Brazil. There are other native palm trees in the region that provide oleaginous fruits rich in provitamins A and E, yet poorly explored, such as pupunha (*Guilielmaspeciosa*) and tucumã (*Astrocaryumvulgare*). These and other vegetable raw materials present in their composition have a high content of lipids, with significant potential for extraction.

Extraction is a unit operation widely used in the food industry and can be used for the production of coffee, sugar, caffeine extraction, vegetable oils, flavorings, and essential oils [54]. Obtaining these extracts may be accomplished by different methods such as mechanical pressing extraction, solvent extraction, supercritical fluids extraction, or others, depending on their content [55–57].

#### **4.1. Mechanical pressing extraction**

The extraction by mechanical pressing is one of the oldest methods of obtaining oil and fats from seed and fruits. For this kind of extraction, the packaged material enters through a feed shaft in the press. The press consists of a basket formed of spaced rectangular steel bars, through blades, whose thickness varies depending on the raw material. In the center of the basket, there is a screw that rotates and moves the material forward, compressing it at the same time. The pressure is regulated via an outlet cone [58, 59].

Souza et al. [60] and Pighinelli et al. [61] report that although the mechanical pressing extraction is less efficient than other methods, it is a more workable system on a small scale, for not being dependent on facilities and safety that are characteristics of the solvent processing, besides being fast, easy to handle and presents low cost of installation and maintenance.

One of the disadvantages of the mechanical pressing method is its low oil yield recovery: even in the most efficient presses, there is still a range of 3–5% of remaining oil in the cake. This residual oil present in the cake can be recovered by a two-step process: pre-extraction (with the screw-press) and solvent extraction, thus maximizing efficiency. Furthermore, the solvent extraction is recommended only in raw materials with <25% of fat content [62–69].

#### **4.2. Solvent extraction**

This type of extraction occurs by partitioning a solute between two immiscible or partially miscible phases. The mass transfer occurs from the solutes in the food matrix to the solvent. First, the solute is dissolved in the solvent, then the penetration of the particle solution in the food surface occurs, and finally the solution is dispersed in the solvent. According to Ghosh [64], solvent extraction can be classified into four types depending on the phase of the matrix: (i) solid-liquid extraction; (ii) liquid-liquid extraction; (iii) vapor extraction; and (iv) supercritical fluids extraction.

The solvent choice is of fundamental importance in the aspects that aim at efficiency, economy, and preservation of the physicochemical and nutritional characteristics of oils. In conventional extraction, some solvents used for obtaining oils from plants are hexane, n-hexane, pentane, ethanol, and petroleum ether [59, 63, 65–70].

In the solvent extraction, there can be a reduction in the product quality because of the several steps necessary to recover the solvent, elevated temperature, long periods of thermal exposure, high oxygen concentration, and extraction of other compounds considered undesirable [63, 71].

#### **4.3. Supercritical fluids extraction**

The supercritical fluids (SCFs) extraction is a unit operation by contact that is based on the balance and on the physicochemical properties of the SCFs, being dependent on operating conditions such as temperature, pressure, solvent flow, the material morphology, prior treatment of the porous solid matrix, and the physical properties of the packed bed, such as porosity, distribution and particle size, initial content of solute in the solid matrix, and the fixed bed height [72].

The SCFs present intermediate characteristics between liquids and gases. The diffusion coefficient (DC) of SCFs is high and close to the gases DC, thus increasing the diffusivity when they are in the liquid state, providing a rapid and efficient mass transfer. The density of SCFs is greater than that of a gas, having a higher solvating power due to the high compressibility. Furthermore, they exhibit low viscosity and the absence of surface tension, which promote greater penetration into the solid matrix [73, 74].

Carbon dioxide (CO2 ) is widely used as SCF due to having low critical temperature and pressure (73.74 bar and 304.12 K, respectively), besides being: nontoxic, nonflammable, odorless, and easily separated from the extract. Due to its low critical temperature, it is possible to use it to extract reactive and thermosensitive compounds. CO2 is suitable for extracting apolar compounds, but when polar organic solvents such as ethyl acetate, ethanol, or methanol are added, the polarity is modified, being possible to extract other compounds. These aggregate solvents are called co-solvents [75].

Batista et al. [8] obtained açaí extracts fractions with supercritical CO2 and analyzed the allelopathic effects of these extracts on two species of invasive plants: *Mimosa pudica* and *Senna obtusifolia*. They observed that depending on the operating conditions of temperature and pressure used, the pattern of phytotoxic responses can change: in some cases, the effect may be stimulatory to seed development. Studies on allelopathy have direct influence on human health, because the use of chemicals such as pesticides, which can cause diseases such as cancer, can be avoided [76–78]. However, other studies must be conducted to isolate the specific metabolites for each role assigned to the açaí.

Pinto [12] also obtained bacaba extracts fractions with supercritical CO2 at different conditions of temperature and pressure. In his work, bacaba is mentioned as a rich source of natural antioxidants and dyes. However, there is a need for further studies to elucidate bacaba's behavior in different processes.

#### **4.4. Other extraction methods**

food surface occurs, and finally the solution is dispersed in the solvent. According to Ghosh [64], solvent extraction can be classified into four types depending on the phase of the matrix: (i) solid-liquid extraction; (ii) liquid-liquid extraction; (iii) vapor extraction; and (iv) super-

The solvent choice is of fundamental importance in the aspects that aim at efficiency, economy, and preservation of the physicochemical and nutritional characteristics of oils. In conventional extraction, some solvents used for obtaining oils from plants are hexane, n-hexane,

In the solvent extraction, there can be a reduction in the product quality because of the several steps necessary to recover the solvent, elevated temperature, long periods of thermal exposure, high oxygen concentration, and extraction of other compounds considered undesirable

The supercritical fluids (SCFs) extraction is a unit operation by contact that is based on the balance and on the physicochemical properties of the SCFs, being dependent on operating conditions such as temperature, pressure, solvent flow, the material morphology, prior treatment of the porous solid matrix, and the physical properties of the packed bed, such as porosity, distribution and particle size, initial content of solute in the solid matrix, and the fixed

The SCFs present intermediate characteristics between liquids and gases. The diffusion coefficient (DC) of SCFs is high and close to the gases DC, thus increasing the diffusivity when they are in the liquid state, providing a rapid and efficient mass transfer. The density of SCFs is greater than that of a gas, having a higher solvating power due to the high compressibility. Furthermore, they exhibit low viscosity and the absence of surface tension, which promote

sure (73.74 bar and 304.12 K, respectively), besides being: nontoxic, nonflammable, odorless, and easily separated from the extract. Due to its low critical temperature, it is possible to use

compounds, but when polar organic solvents such as ethyl acetate, ethanol, or methanol are added, the polarity is modified, being possible to extract other compounds. These aggregate

lopathic effects of these extracts on two species of invasive plants: *Mimosa pudica* and *Senna obtusifolia*. They observed that depending on the operating conditions of temperature and pressure used, the pattern of phytotoxic responses can change: in some cases, the effect may be stimulatory to seed development. Studies on allelopathy have direct influence on human health, because the use of chemicals such as pesticides, which can cause diseases such as cancer, can be avoided [76–78]. However, other studies must be conducted to isolate the specific

) is widely used as SCF due to having low critical temperature and pres-

is suitable for extracting apolar

and analyzed the alle-

critical fluids extraction.

**4.3. Supercritical fluids extraction**

[63, 71].

bed height [72].

Carbon dioxide (CO2

solvents are called co-solvents [75].

metabolites for each role assigned to the açaí.

pentane, ethanol, and petroleum ether [59, 63, 65–70].

164 Superfood and Functional Food - An Overview of Their Processing and Utilization

greater penetration into the solid matrix [73, 74].

it to extract reactive and thermosensitive compounds. CO2

Batista et al. [8] obtained açaí extracts fractions with supercritical CO2

The methods of soxhlet, hydrodistillation, solid-liquid, and ultrasound-assisted extraction do not present a performance as good as the one presented by the extraction with supercritical fluids: it has a high selectivity, low or no organic solvent consumption, operates at temperature close to room, no request for subsequent purification steps, and reduces post-processing costs as there is no longer need to eliminate solvent extracts [75, 79, 80].
