Phytochemical, nutritional and antioxidant characteristics of whitebeam (Sorbus aria) fruits

BACKGROUND

Common whitebeam, Sorbus aria (L.) Crantz is an European and Near-Eastern deciduous tree with small red fruits. However, the edible use of this forest fruit is currently not widespread. Also, its nutritional and antioxidative properties remained undiscovered. In this study, the chemical composition and antioxidant properties of common whitebeam fruit were investigated.

METHODS

The fruit were collected from Golo Bardo Mountain in Bulgaria. The phytochemical (carotenoids, phenolic compounds, flavonoids), nutritional (moisture, ash, titrable acidity, lipids, proteins, pectin, carbohydrates) and antioxidant activity were evaluated by four assays (DPPH, ABTS, FRAP, and CUPRAC).

RESULTS

Sugar analysis demonstrated that only fructose and glucose were detected in the fruit. Pectin content did not exceed 1.30%. Moreover, the fruit had a low lipid content (0.80%). The whitebeam fruit were also characterized as a source of carotenoids (1.69 mg/100 g fresh weight, fw), phenolic compounds (32.42 mg GAE/100 g fw), and flavonoids (20.08 mg QE/100 g fw). Among phenolic acids, only 2,4-dihydrohybenzoic, caffeic, p-coumaric, and sinapic acid were detected. The antioxidant potential of the fruit was from 168.52 mM TE/100 g fw (FRAP) to 244.81 mM TE/100 g fw (CUPRAC assay).

CONCLUSIONS

The current research enriched the available information about the nutritional potential and chemical composition of common whitebeam fruit and their low sugar content. The absence of sucrose, together with its high phenolic content, demonstrated the potential of this fruit for future application in food products and supplements.

Modelling the mechanical behaviour of pit membranes in bordered pits with respect to cavitation resistance in angiosperms

BACKGROUND AND AIMS

Various correlations have been identified between anatomical features of bordered pits in angiosperm xylem and vulnerability to cavitation, suggesting that the mechanical behaviour of the pits may play a role. Theoretical modelling of the membrane behaviour has been undertaken, but it requires input of parameters at the nanoscale level. However, to date, no experimental data have indicated clearly that pit membranes experience strain at high levels during cavitation events.

METHODS

Transmission electron microscopy (TEM) was used in order to quantify the pit micromorphology of four tree species that show contrasting differences in vulnerability to cavitation, namely Sorbus aria, Carpinus betulus, Fagus sylvatica and Populus tremula. This allowed anatomical characters to be included in a mechanical model that was based on the Kirchhoff-Love thin plate theory. A mechanistic model was developed that included the geometric features of the pits that could be measured, with the purpose of evaluating the pit membrane strain that results from a pressure difference being applied across the membrane. This approach allowed an assessment to be made of the impact of the geometry of a pit on its mechanical behaviour, and provided an estimate of the impact on air-seeding resistance.

KEY RESULTS

The TEM observations showed evidence of residual strains on the pit membranes, thus demonstrating that this membrane may experience a large degree of strain during cavitation. The mechanical modelling revealed the interspecific variability of the strains experienced by the pit membrane, which varied according to the pit geometry and the pressure experienced. The modelling output combined with the TEM observations suggests that cavitation occurs after the pit membrane has been deflected against the pit border. Interspecific variability of the strains experienced was correlated with vulnerability to cavitation. Assuming that air-seeding occurs at a given pit membrane strain, the pressure predicted by the model to achieve this mechanical state corresponds to experimental values of cavitation sensitivity (P50).

CONCLUSIONS

The results provide a functional understanding of the importance of pit geometry and pit membrane structure in air-seeding, and thus in vulnerability to cavitation.

Cytotype diversity in the Sorbus complex (Rosaceae) in Britain: sorting out the puzzle

BACKGROUND AND AIMS

Large-scale ploidy surveys using flow cytometry have become an essential tool to study plant genome dynamics and to gain insight into the mechanisms and genetic barriers framing ploidy diversity. As an ideal complement to traditional techniques such as chromosome counting, the analysis of cytotype diversity in plant systems such as Sorbus provides primary investigation into the potential patterns and evolutionary implications of hybrid speciation.

METHODS

Ploidy was assessed by means of relative nuclear DNA content using propidium iodide flow cytometry in 474 Sorbus samples collected from 65 populations in southern Wales and South-West England. Statistical tests were applied to evaluate the utility of this technique to confidently discriminate ploidy in the genus.

KEY RESULTS

Flow cytometric profiles revealed the presence of four cytotypes (2x, 3x, 4x and 5x), confirming in many cases chromosome counts previously reported and demonstrating cytotype heterogeneity within specific Sorbus aggregates. Diploid cytotypes were restricted to the potential parental species and homoploid hybrids. Most of the samples processed were polyploid. The occurrence of the pentaploid cytotype had previously only been reported from a single specimen; it is now confirmed for two taxa occurring at different sites.

CONCLUSIONS

Flow cytometry results obtained have proved useful in shedding light on the taxonomy of several controversial taxa and in confirming the presence of cytoypes which occur at very low frequencies. Notably, the coexistence of several cytotypes in Sorbus populations has probably been facilitated by the overlapping distribution of many of the species studied, which might also explain the high incidence of potential hybrid apomictic polyploids. These results will provide a solid baseline for molecular research aiming to better understand the genetic pathways controlling the formation and establishment of polyploid Sorbus.