Seed maturation is a key stage in the life cycle of a plant and ensures its subsequent propagation and distribution [1]. Seed quality is essential for industrial-scale agricultural production and food security [2]. Our basic needs are directly or indirectly related to trees as a source of water, food, housing, health, and education [3]. Although climate change threatens some forest ecosystems, forests can influence the course of climate change by regulating water regimes, air quality, and carbon sequestration [4]. As shown for Euterpe edulis Martius, strategies aimed at improving seed maturation, germination, and seedling production can mitigate the effects of climate change [[5], [6], [7]].

E. edulis belongs to the Arecaceae family, known as juçara, and is native to the Atlantic Forest [8]. Its fruits are similar to the açaí berries of Euterpe oleracea Martius and Euterpe precatoria Martius [9]. However, the pulp of E. edulis fruits has superior bioactive properties, higher antioxidant potential, and richer nutritional composition [8,[10], [11], [12]]. Thus, its fruits have gained growing attention, making their harvesting an economic and sustainable source of income that does not threaten biodiversity.

The fruits are small, with a diameter of 1.0–1.5 cm, and the seeds constitute 85 % of the fruit [13]. The small embryo comprises only 0.54 % of the seed fresh weight, whereas the massive endosperm constitutes the remaining 99 % [14]. Germination occurs unevenly after 60–90 days [15], because the hardness of mature endosperm makes it difficult for the embryo to germinate [5]. This leads also to high seedling mortality during the first years [16]. Seed germination and seedling growth are influenced by the type and amount of primary metabolites transferred from the mother plant and are used as reserves for embryo growth [17,18].

The main reserve in Arecaceae is the mannan present in the cell wall, which provides mechanical strength and protection to developing embryos. However, the mechanical resistance offered by mannan results in a long germination period, as it requires considerable growth by the embryo [19,20]. Endo-β-mannanase, which is involved in the mobilization of mannan reserves, plays a central role in establishing the endosperm digestion zone in several species of palms, such as Phoenix dactylifera [21], Elaeis guineensis [22], Acrocomia aculeata [23], Butia capitata [24], and E. oleracea [25].

Sugars and organic acids are the main soluble constituents of fruits and are involved in the biosynthesis of amino acids, vitamins, and volatile compounds [26]. Despite the relevance of sugars, few studies have evaluated their content in juçara fruit pulp [[27], [28], [29]]. Mello et al. [5] studied the content of lipids, total sugars, starch, and proteins throughout seed maturation, but only in a few stages and without assessing sugar composition.

Thus, the objective of this study was to assess whether the amount of monosaccharides and the level of crystallinity changed during seed maturation, along with establishing a link between the crystallinity of mannan and the germination capacity and vigor of seedlings. This study opens up a range of possibilities for improving the production of juçara seedlings, as well as the propagation of other forest species, for which mannan is also the main macromolecule in the seeds.