**2. Biology**

#### **2.1 Taxonomic classification and distribution**

Macauba is a palm species that belongs to the Arecaceae family, which includes approximately 189 genera and about 3000 species, which are classified into five subfamilies, as follows: Calamoideae, Nypoideae, Coryphoideae, Ceroxyloideae, and Arecoideae [21]. The latter is the most representative family since it contains species of great economic interest such as *Elaeis guineensis* (African palm), *Cocos nucifera*, *Euterpe oleracea,* and the emerging species *Acrocomia aculeata* (macauba) [21]. The great phenotypic diversity among individuals of *A. aculeata* (Jacq.) Lodd. ex-Mart has led to a misunderstanding about the number of species that belong to the genus *Acrocomia*. For this reason, there is still no consensus on the taxonomy of this genus [22]. Recent studies using both morphoanatomical characteristics of the plant and fruit biometrics have contributed to the understanding of the taxonomy of this group [23–27].

Currently, nine species are included within the genus *Acrocomia* that occur in the Neotropical region, including *A. aculeata*, *A. crispa*, *A. emensis*, *A. corumbaensis*, *A. glaucescens*, *A. hassleri*, *A. intumescens*, *A. media*, and *A. totai* [22]. Fossil studies and the great phenotypic diversity of the genus *Acrocomia* suggest that Brazil may be the center of origin and dispersal of these species [28], probably due to both weathering processes and human activity in the Americas [22]. The species *A. aculeata* is endemic to Brazil and has been distributed to islands in the Caribbean, Central America, and South America [22]. In Brazil, this palm occurs in most of the territory, mainly in the states of Minas Gerais, São Paulo, Goias, Mato Grosso, and Mato Grosso do Sul, in the Cerrado [22, 29]. It can also be found in tropical and subtropical forests, and dry forests of Caatinga [23, 30], with good adaptation to sandy soils and regions with low water availability [24].

#### **2.2 Morphology and reproduction**

Macauba is a perennial, halophytic, tree-like palm species with a solitary, aerial, cylindrical, and spindle-shaped stem that can reach 10–15 m in height and 20–30 cm in diameter. The stipe is often covered by the bases of the petioles, which remain

attached for many years. The node region is covered with dark and sharp spines and is approximately 10 cm long [31].

The *A. aculeata* genome has 2.8 Gbp distributed on 15 pairs of chromosomes (2n = 30) with an AT base content of 58.3% [32]. This palm is monoecious and presents interfoliate and branched spadix-like yellow inflorescences 50–80 cm long. It presents a large number of staminate flowers at the base and pistillate flowers originate triad at the top of the inflorescence [30, 33]. Although the reproductive system is cross-pollination between different individuals, the species is self-compatible [33]. Entomophily is the main pollination route, and anemophily plays a secondary role. Scariot et al. suggested that the combination of these two types of pollination with a flexible reproductive system is related to the wide distribution of the species [33].

Macauba flowering is seasonal and annual. In Brazil, it blooms from September to February, with peak flowering in November and December [33]. However, fruiting occurs throughout the year and the fruits mature approximately 1 year after fertilization [33]. Macauba generates inflorescences with bulky clusters that contain 300–600 drupaceous fruits, weighing about 66 g/each, resulting in a highly productive plant [13].

The fruits can be 3.0–5.0 cm in diameter, are edible, spherical, and do not ferment immediately after ripening [5]. The fruit contains approximately 20% epicarp (peel), 40% mesocarp (pulp), 33% endocarp, and 7% kernel [34]. The epicarp ruptures easily when ripe. The mesocarp is fibrous, mucilaginous, sweet-tasting, edible, and rich in glycerides, yellow or whitish in color. The endocarp is strongly adhered to the pulp, with a black bony wall, and an edible oily kernel covered by a thin layer of the tegument. Each fruit usually contains a seed surrounded by a hard, dark endocarp approximately 3-mm thick [30, 35]. Macauba has two economically important kinds of oil, stored in the fruit pulp and its kernel. The pulp contains up to 75% of the total lipids, while the kernel may contain up to 65%, both on a dry basis [34]. **Table 1** shows the proximate composition of *A. aculeata* pulp and kernel.

### **2.3 Domestication and plant breeding**

Macauba, like most palm species, has an essentially extractive cultivation system, leading to habitat fragmentation, increasing inbreeding, and decreasing genetic diversity [37]. Both the domestication process and the development of breeding programs for *A. aculeata* are still at an incipient stage [27, 38]. However, its domestication


#### **Table 1.**

*Proximate composition of macauba fruit. Source: Lira et al. [36].*

#### *Macauba (*Acrocomia aculeata*): Biology, Oil Processing, and Technological Potential DOI: http://dx.doi.org/10.5772/intechopen.105540*

should be integral and systematic due to the socioeconomic impact of the cultivation of this palm and the application prospects [7]. The success of the domestication process depends on genetic improvement programs that are directly related to the choice of genotypes with the best agronomic characteristics [39]. Knowledge about the genetic diversity of *A. aculeata* is fundamental to guiding the selection of the most promising materials for use in the crop, maximizing genetic gains, and contributing to the creation of commercial cultivars [38]. Colombo et al. pointed out the main guidelines for the improvement of *Acrocomia* plants, including obtaining varieties with optimized height, greater drought tolerance, and higher oil productivity [5].

There is great morphometric and genetic variability among macauba plants native to the Brazilian Cerrado and Pantanal regions of Brazil and Costa Rica, characterized by fruit biometry and oil yield [34, 40, 41]. However, these factors are not correlated [40]. Biometric studies of Costa Rican varieties have suggested a possible environmental effect on oil composition and yield [41]. Dos Santos et al. [42] studied the accumulation of metabolites in fruits coming from three Brazilian regions (Southeast, Northeast, and Midwest) characterized by having different lipid contents. The authors concluded that, despite the anatomical differences between mesocarp and endocarp, in both tissues, a similar trend of metabolite accumulation was observed toward ripening. In the mesocarp, total soluble proteins, free amino acids, sucrose, starch, and total lipids accumulate toward maturity, with a decrease in glucose and fructose contents. The endosperm differed from the mesocarp only for the amino acid contents, which decreased in mature fruits. The results pointed out that fruits from the Southeast region (Minas Gerais) may be of interest for breeding studies due to their higher lipid contents [42].

Genomics-based strategies allow access to the genetic potential of natural populations, germplasm characterization, phylogenetic analysis, etc. [38]. The availability of public databases (www.ncbi.nhi.gov) of genomic sequences of *A. aculeata* has enabled great advances in genetic variability studies in the last decade. Those studies confirm the high genetic diversity among varieties, allowing the identification of genotypes with the highest agronomic potential, the abiotic factors related to increased oil production, and the efficiency of biosynthesis, evolution, and phylogeny of this species [32, 40, 43–45].

The embryo culture of *A. aculeata* allows the achievement of high germination rates, solving the deep seed dormancy that causes low germination rates [46]. However, the acclimation process restricts seedling growth. Recent histological studies have pointed to impaired development of the haustoria, root system, and leaves as the possible causes of this phenomenon [18]. Souza et al. [47] evaluated the effects of climate seasonality on the longevity and dormancy of diaspores of macauba palm. That approach is critical for establishing soil seed banks that allow for the conservation of natural populations and extractive management. The authors reported that the longevity of macauba seeds in the soil depends on several factors, including the maintenance of structural protection of the embryo, tolerance to water deficits, and control of oxidative stress. In turn, the overcoming of dormancy is related to the gradual weakening of the containment tissues and the strength of the embryo [47].

In this context, the development of genetic improvement programs for macauba to allow systematic cultivation and commercialization on a large scale in the near future is required. Initiatives to cultivate macauba in Brazil for commercial purposes have been undertaken, including the programs Entaban Brazil, Solea, and Inocas, with production destined for national consumption [5].
