Carbohydrate and fibre fractions of the fruit of Hyphaene coriacea Gaertn.: compositional characterisation and potential nutritional interest

1. Introduction

Carbohydrates are a major source of dietary energy, yet their metabolic effects differ according to their chemical structure, degree of polymerisation, and digestibility (Slavin, 2013a; Cummings and Stephen, 2007). In contrast to digestible carbohydrates, dietary fibres escape enzymatic digestion in the small intestine and reach the colon, where they may be partially fermented by the gut microbiota (Soliman, 2019). Owing to their physicochemical properties, dietary fibres are involved in several mechanisms that may influence the postprandial glycaemic response, notably delayed gastrointestinal transit, modulation of nutrient absorption, and improvement of metabolic control. Consistently, epidemiological and interventional data indicate that a high intake of dietary fibre is associated with improved glycaemic control and a reduced risk of type 2 diabetes (Reynolds et al., 2019; Weickert and Pfeiffer, 2018; Threapleton et al., 2013; Blaak et al., 2020).

The nutritional interest of carbohydrate-rich foods depends, however, not only on their total carbohydrate content, but also on the nature of the available sugars and their association with fibre fractions within the food matrix. Foods characterised by a low proportion of rapidly available sugars and a high proportion of cell wall components, such as cellulose and lignin, may be of particular interest in nutritional approaches aimed at attenuating the postprandial glycaemic response (Slavin, 2005; Dhingra et al., 2012; McRae, 2018). In this perspective, the combined characterisation of available carbohydrate fractions and fibrous constituents represents an important step in evaluating the nutritional potential of a plant-derived food.

Among still poorly documented plant resources, traditionally consumed palm fruits constitute a group of interest. Although several species are valued in local food systems, their detailed carbohydrate and fibre profiles often remain insufficiently characterised (Slavin, 2005; Wong and Jenkins, 2007). Hyphaene coriacea Gaertn. (Arecaceae) is consumed in several regions of Africa, including Madagascar, where the fruit is used fresh or in processed form, particularly as flour (Dransfield et al., 2008). Despite this food use, the main carbohydrate fractions and fibrous components of H. coriacea Gaertn. fruit have not been characterised comprehensively, which limits the objective assessment of its nutritional interest in the context of glycaemic control.

The present study was therefore undertaken to characterise the main carbohydrate and fibre fractions of the whole fruit of H. coriacea Gaertn. We hypothesised that this fruit would display a low content of rapidly available sugars together with a substantial proportion of structural fibre fractions, consistent with potential nutritional relevance in dietary approaches targeting glycaemic control. By providing original compositional data, this study aims to improve knowledge of the nutritional value of H. coriacea Gaertn. fruit and to establish an analytical basis for future investigations into its relevance in food-based strategies oriented towards glycaemic control.

2. Materials and methods

3. Results

The results relating to the carbohydrate composition, crude fibre and lignin contents, derived carbohydrate-to-fibre ratios, and the estimated theoretical energy contribution of the carbohydrate fraction of H. coriacea Gaertn. fruit are presented below.

4. Discussion

The fruit of H. coriacea Gaertn. exhibited a compositional profile dominated by total carbohydrates, within which starch constituted a notable identified fraction, whereas soluble sugars remained weakly represented. At the same time, crude fibre and estimated lignin reflected a plant matrix rich in structural constituents. Taken together, these findings describe a whole fruit with marked cell wall organisation. The physiological implications of this architecture, notably for carbohydrate digestibility and the postprandial glycaemic response, nevertheless require confirmation by dedicated functional studies.

Total carbohydrate content reached 87.80 ± 1.44% DM, a value higher than those reported for other species of the same genus. For comparison, the pulp of Hyphaene thebaica has been reported to contain lower carbohydrate levels, ranging from 68.47% (Datti et al., 2020) to 69.33% (Alagbe, 2024). Marked variation has also been described according to the anatomical part of the fruit analysed, with values of 72.5% in the flesh and 44.2% in the epicarp (Aboshora et al., 2014), whereas some analyses of the mesocarp have reported contents as high as 83.7% (Bello et al., 2021).

The residual carbohydrate fraction, estimated at 53.59 ± 3.09% DM, indicates that a substantial proportion of total carbohydrates is not accounted for by the crude fibre fraction. This estimate should, however, be interpreted with caution, since the crude fibre method reflects only a limited part of total dietary fibre. Consequently, the resulting value cannot be assimilated to a direct measure of available carbohydrates and may lead to overestimation of the fraction that is actually digestible and absorbable.

Overall, the carbohydrate values obtained for H. coriacea Gaertn. fall within the ranges reported for related palm species while also highlighting certain compositional specificities. The discrepancies observed across studies are probably attributable, to a large extent, to the nature of the plant fraction analysed. Most studies devoted to H. thebaica have focused on the pulp, generally richer in soluble carbohydrates, whereas the present study examined the whole fruit, including structural and partially lignified cell wall tissues. Additional sources of variation may also be invoked, notably fruit maturity stage, environmental conditions, genetic background, and the analytical approaches employed (Ullah et al., 2023; Rivera et al., 2016).

The combined profile of total carbohydrates and the residual carbohydrate fraction in H. coriacea Gaertn. fruit suggests a matrix dominated by structurally integrated carbohydrate fractions. The accessibility of these polysaccharides to digestive enzymes may be limited by their incorporation into a dense plant matrix, which could contribute to slowing their hydrolysis and, potentially, attenuating the postprandial glycaemic response. This interpretation nevertheless remains indirect and is based on compositional rather than functional data. It remains, however, consistent with previous work describing the metabolic effects of complex carbohydrates and dietary fibre (Slavin, 2013b; Reynolds et al., 2019), as well as with nutritional recommendations favouring carbohydrate sources with a low glycaemic index (Jenkins et al., 2002).

The fruit displayed very low levels of soluble sugars, with total sugars reaching 3.91 ± 0.00% DM, no detectable reducing sugars, and sucrose accounting for 3.71 ± 0.00% DM, indicating a very limited contribution of simple sugars and the absence of detectable reducing sugars under the analytical conditions used. This result does not, however, allow the conclusion that free glucose or fructose are absolutely absent.

Available data indicate that H. thebaica contains higher levels of soluble sugars than those quantified in the present study. Farag and Paré (2013) showed that sucrose was the principal soluble sugar in H. thebaica, with concentrations reaching 219 mg g⁻¹. It has also been established that variation in free sugar content depends strongly on the anatomical fraction analysed, tissue organisation, and fruit maturity stage (Cakpo et al., 2020), which provides a plausible explanation for the lower values observed here, since the analysis was performed on the whole fruit rather than on the pulp alone. The high density of cell wall tissues, enriched in pectins, celluloses and hemicelluloses, is indeed known to limit solute diffusion and restrict the accessibility of intracellular sugars within the plant matrix (Voragen et al., 2009).

In palm species, sugar accumulation profiles are also influenced by fruit ripening, with simple sugar concentrations generally increasing during maturation, as reported in Phoenix dactylifera (Diboun et al., 2015). In addition, post-harvest treatments, particularly drying and storage, may induce quantitative or qualitative changes in free sugar composition. Methodological factors may likewise contribute to the discrepancies observed across studies, since colorimetric or titrimetric assays have more limited analytical specificity than chromatographic approaches, which allow more sensitive and selective characterisation of individual sugars (Nielsen, 2010).

Despite these low soluble sugar levels compared with H. thebaica, the values obtained in the present study remain consistent with the compositional characteristics of a whole fruit rich in cell wall-derived constituents and possibly corresponding to a distinct physiological stage (Seymour et al., 2013). Such structural organisation, dominated by cell wall polysaccharides and characterised by a low abundance of simple sugars, could contribute to limiting rapid postprandial increases in blood glucose. Although sucrose is a soluble disaccharide, its effective accessibility to digestive enzymes may be reduced when embedded within a dense plant matrix, which could delay its hydrolysis and the subsequent appearance of glucose in the circulation (Slavin, 2013b; Giuntini et al., 2022).

Consequently, the low simple sugar content measured in H. coriacea Gaertn. fruit suggests a potentially limited contribution to rapid glycaemic responses. Such a profile, comparable to that observed in foods naturally low in simple sugars, is generally associated with slower intestinal absorption kinetics (Beckles, 2012) and lower glycaemic potential (Reynolds et al., 2019).

Starch content in H. coriacea Gaertn. fruit reached 13.56 ± 0.27% DM, indicating that starch represents a substantial, although not predominant, fraction of total carbohydrates. In the absence of comparable starch data for other species of the genus Hyphaene, this value should above all be regarded as a compositional reference within palm fruits characterised by limited starch accumulation. Within the Arecaceae family, starch contents are indeed highly variable, with values reaching 80 to 90% DM in Bactris gasipaes (Alves et al., 2015; Rosário et al., 2025). By contrast, ripe fruits of P. dactylifera are largely dominated by soluble sugars and dietary fibre, with starch being virtually absent (Booij et al., 1992; Al-Karmadi and Okoh, 2024).

The starch content observed in H. coriacea Gaertn. fruit thus lies in the lower range of values reported for Arecaceae species and may reflect both the relatively high content of structural fibre in the whole fruit and differences related to analytical approaches (Ferrari et al., 2020). From a physiological perspective, starch generally persists at moderate levels in tissues at less advanced stages of maturation, whereas simple sugars become predominant at later ripening stages, a pattern frequently reported in Arecaceae fruits (Chandrasekaran and Bahkali, 2013).

The intermediate starch level observed in H. coriacea Gaertn. fruit probably reflects the combined influence of physiological and structural factors. Fruit developmental stage plays an important role, since starch accumulated during the early phases of growth is progressively converted into soluble sugars through activation of amylolytic enzymes during ripening (Li et al., 2021). In addition, the presence of a dense lignocellulosic matrix may reduce the accessibility of starch granules to extraction solvents and digestive enzymes, thus affecting both analytical recovery and hydrolysis rate (Hansen et al., 2013; Zhang et al., 2020).

The starch fraction quantified in the present study is therefore consistent with the presence of carbohydrate components likely to be digested more slowly than rapidly available simple sugars. Depending on its physicochemical organisation within the matrix, part of this fraction may exhibit limited enzymatic accessibility. Such structural constraints could contribute to slower glucose release during digestion and, consequently, to a more moderate postprandial glycaemic response (Jenkins et al., 1981; Miao et al., 2015). However, resistant starch was not directly measured in the present study, and any inference regarding its presence, digestive fate, or colonic fermentation remains hypothetical. If a fraction of this starch were indeed to escape digestion in the small intestine and reach the colon, its microbial fermentation could lead to the production of short-chain fatty acids, notably butyrate and propionate, metabolites associated with favourable effects on insulin sensitivity and carbohydrate metabolism (Birt et al., 2013; Robertson et al., 2005).

The fruit of H. coriacea Gaertn. exhibited a marked lignocellulosic profile, characterised by a crude fibre content of 34.21 ± 1.66% DM and an estimated lignin content of 18.08 ± 0.65% DM.

In date palms (P. dactylifera), the fibre fraction is likewise largely dominated by cellulose, hemicelluloses and lignin, with insoluble components accounting for most of the total dietary fibre (Sejpal et al., 2025; Ibrahim et al., 2021). In several cultivated varieties, total dietary fibre contents range from 3.2 to 7.4 g/100 g fresh fruit, of which more than 90% correspond to insoluble lignocellulosic components (Okonkwo et al., 2025). Such structural organisation contributes to rigidity of the cell wall tissues and directly influences fruit texture, mechanical hardness, and the accessibility of carbohydrates to digestive enzymes.

The lignocellulosic values obtained for H. coriacea Gaertn. fruit fall within the compositional range reported for highly fibrous palm tissues, although they appear higher than most published values. This observation remains plausible insofar as the present study was conducted on the whole fruit, including the pericarp and other structurally reinforced tissues. Several factors may contribute to these elevated levels. From an anatomical perspective, the predominance of lignocellulosic bundles and thickened cell walls is a major determinant of fibre abundance (Asp et al., 1983). The presence of vascular elements and sclerenchymatous tissues may also increase the proportion of structural polysaccharides (Al-Shahib and Marshall, 2003). In addition, estimation of lignin by NIRS may introduce a degree of uncertainty, particularly in highly lignified matrices, depending on calibration quality and the physical characteristics of the sample, notably its residual moisture content (Cozzolino et al., 2001; Foley et al., 1998). Finally, the low water content of the samples and the concentration effect associated with drying are likely to increase the relative proportion of fibre when results are expressed on a dry matter basis (Al-Farsi and Lee, 2008).

The high abundance of insoluble fibre, cellulose and lignin in H. coriacea Gaertn. fruit suggests the presence of a dense plant matrix likely to restrict the accessibility of digestive enzymes to carbohydrate substrates. Such structural constraints are known to modulate gastrointestinal processes, notably by slowing gastric emptying, increasing satiety, and limiting the extent of carbohydrate hydrolysis, which may contribute to attenuating postprandial glycaemic responses (Taghipoor et al., 2014; Stephen et al., 2017). Evidence from controlled clinical studies further indicates that diets enriched in insoluble or mixed fibres are associated with reductions in fasting blood glucose, glycated haemoglobin, and certain markers of insulin resistance (Reynolds et al., 2020). In this context, the compact lignocellulosic architecture of the fruit could constitute an important factor influencing carbohydrate digestion kinetics (Cho et al., 2013).

The compositional characteristics observed for H. coriacea Gaertn. fruit show certain analogies with those reported for several plant-derived foods recognised for the metabolic relevance of their carbohydrate and fibre fractions. For example, the pulp of Adansonia digitata, characterised by high fibre content and relatively low levels of simple sugars, has shown the ability to attenuate postprandial glycaemic responses (Rita et al., 2022; Silva et al., 2023). Likewise, pectins from Citrus sinensis increase intestinal viscosity and delay carbohydrate absorption, mechanisms incorporated into certain nutritional recommendations (Blanco-Pérez et al., 2021; FSANZ, 2016). In addition, galactomannans derived from Trigonella foenum-graecum , which are highly viscous soluble fibres, have been reported to reduce glycated haemoglobin and slow glucose absorption (Neelakantan et al., 2014). Taken together, these observations support the hypothesis that H. coriacea Gaertn. fruit may be of nutritional interest in the context of glycaemic control, although its specific physiological effects remain to be confirmed experimentally.

Total carbohydrates accounted for 87.80% DM in H. coriacea Gaertn. fruit and, on this basis, constituted the principal fraction contributing to the estimated theoretical energy value. This compositional profile indicates that the fruit is predominantly composed of carbohydrates when expressed on a dry matter basis, while also containing a substantial proportion of crude fibre (34.21% DM). Taken together, these elements support the relevance of considering this fruit as a structurally complex plant matrix, potentially pertinent within balanced dietary patterns aimed at glycaemic regulation. This interpretation is consistent with the previously cited literature highlighting the combined influence of carbohydrate quality and fibre on postprandial glycaemic responses.

Analysis of carbohydrate ratios further clarifies the qualitative balance of the carbohydrate fraction. The proportion of the residual carbohydrate fraction remained moderate relative to total carbohydrates (residual carbohydrate fraction/total carbohydrates = 0.61), whereas the contribution of simple sugars to the residual carbohydrate fraction remained low (total sugars/ residual carbohydrate fraction = 0.07; sucrose/ residual carbohydrate fraction = 0.07). Such ratios suggest a low contribution of rapidly absorbable carbohydrates, generally associated with rapid postprandial glycaemic excursions (FAO/WHO, 1998). In addition, the moderate contribution of starch (starch/residual carbohydrate fraction = 0.25) is compatible with a potentially more gradual release of glucose than that expected in a matrix dominated by simple sugars (Englyst et al., 1992).

The fibre/carbohydrate ratios further revealed a clear predominance of structural fractions, particularly crude fibre (0.64) and lignin (0.34), relative to the residual carbohydrate fraction. Such a compositional balance could contribute to delaying carbohydrate digestion and reducing enzymatic accessibility within the plant matrix (Livesey, 2001).

When expressed relative to total sugars, the high ratios observed for crude fibre (8.75) and lignin (4.62) further underline the low density of rapidly assimilable sugars within the fruit matrix. Taken together, these quantitative relationships are consistent with a potential attenuation of postprandial glycaemic responses, primarily mediated by the modulatory effects of structural fibres on carbohydrate absorption kinetics, without implying a demonstrated hypoglycaemic effect under in vivo conditions (FAO/WHO, 1998).

Taken together, the calculated ratios provide a coherent quantitative framework for integrated interpretation of the compositional data. They should not, however, be considered direct predictors of clinical outcomes, but rather descriptive compositional indicators reflecting the balance between carbohydrate fractions and structural fibres within the fruit matrix.

This study provides the first detailed compositional data on H. coriacea Gaertn. fruit, including characterisation of its carbohydrate fraction and structural fibre fractions. These findings contribute to advancing knowledge on still underexplored palm fruits and establish a basis for future research in functional nutrition, particularly with regard to carbohydrate quality and dietary strategies relevant to glycaemic regulation. They notably highlight the importance of investigating in greater detail the digestibility, structural organisation and fermentability of fibre fractions, as well as their potential influence on parameters related to the glycaemic index.

From a nutritional perspective, the compositional characteristics of the fruit, as analysed in dried and powdered form, suggest potential applicability in dietary patterns aimed at moderating postprandial glycaemic responses, enhancing satiety, and supporting body weight regulation. Beyond nutritional considerations, the valorisation of H. coriacea Gaertn. as a local food resource may also be of socio-economic interest by contributing to food security and promoting the use of endogenous plant species in community-based approaches to metabolic health.

Nevertheless, several limitations of the present study should be acknowledged. First, the findings are based exclusively on compositional analyses and do not include direct assessment of carbohydrate digestibility under either in vitro or in vivo conditions. Second, the specific nature of the starch fraction, rapidly digestible starch, slowly digestible starch, or resistant starch, was not determined, despite its important role in modulating postprandial glycaemic responses. Third, the absence of detailed characterisation of soluble fibre fractions limits interpretation of the potential physiological effects. In addition, because crude fibre quantification captures only a limited portion of total dietary fibre, the calculated content of the residual carbohydrate fraction may overestimate the proportion of carbohydrates that is actually available for digestion. Moreover, the predominance of insoluble and potentially poorly fermentable structural fractions requires further investigation in order to clarify their metabolic relevance. Finally, the use of an NIRS-based prediction for lignin quantification may introduce estimation uncertainty, which underlines the need for validation by reference analytical methods.

These limitations identify several priority directions for future research. Further work should aim to characterise starch fractions in order to refine understanding of carbohydrate hydrolysis kinetics and glucose release profiles. in vitro digestibility assays simulating gastrointestinal conditions would be useful to evaluate the resistance of the lignocellulosic matrix to enzymatic degradation. in vivo studies, initially in animal models and subsequently in humans, will be required to confirm effects on postprandial glycaemia and to define relevant intake levels. Finally, assessment of technological processing approaches, including cooking, milling, drying and granulation, would help identify the nutritionally most relevant forms of the fruit while preserving, as far as possible, its functional properties.