Abstract
The water soluble carbohydrates (WSC) glucose, fructose, and sucrose are well-known to the great public, but fructans represent another type of WSC that deserves more attention given their prebiotic and immunomodulatory properties in the food context. Although the occurrence of inulin-type fructo-oligosaccharides (FOS) was proposed in the fruit of some banana accessions, little or no information is available neither on the exact identity of the fructan species, nor on the fructan content in different parts of banana plants and among a broader array of banana cultivars. Here, we investigated the WSC composition in leaves, pulp of ripe fruits and rhizomes from mature banana plants of 11 accessions (I to XI), including both cultivated varieties and wild Musa species. High performance anion exchange chromatography with integrated pulsed amperometric detection (HPAEC-IPAD) showed the presence of 1-kestotriose [GF2], inulobiose [F2], inulotriose [F3], 6-kestotriose and 6G-kestotriose (neokestose) fructan species in the pulp of mature fruits of different accessions, but the absence of 1,1-nystose and 1,1,1 kestopentaose and higher degree of polymerization (DP) inulin-type fructans. This fructan fingerprint points at the presence of one or more invertases that are able to use fructose and sucrose as alternative acceptor substrates. Quantification of glucose, fructose, sucrose and 1-kestotriose and principal component analysis (PCA) identified related banana groups, based on their specific WSC profiles. These data provide new insights in the biochemical diversity of wild and cultivated bananas, and shed light on potential roles that fructans may fulfill across species, during plant development and adaptation to changing environments. Furthermore, the promiscuous behavior of banana fruit invertases (sucrose and fructose as acceptor substrates besides water) provides a new avenue to boost future work on structure-function relationships on these enzymes, potentially leading to the development of genuine banana fructosyltransferases that are able to increase fructan content in banana fruits.
Highlights
One of the most widespread alternatives to starch or sucrose as reserve carbohydrates are fructans, which are produced by about 15% of flowering plant species (Hendry, 1993)
Biochemical Diversity of water soluble carbohydrates (WSC) in Different Organs from 11 Accessions of Banana The non-reducing GFn type of fructans 1-kestotriose, 6kestotriose and 6G-kestotriose, as well as the reducing inulo-n-oses or Fn type fructans inulobiose (F2) and, to a lesser extent, inulotriose (F3), could be clearly detected in the pulp of ripe fruit, and to a lower degree, in the leaves and rhizomes of three of the wild Musa accessions, which are in the ancestry of the cultivated bananas
Of the three putative inulin-type fructan peaks detected by HPLC-RID, only 1-kestotriose was validated by HPAEC-IPAD
Summary
One of the most widespread alternatives to starch or sucrose as reserve carbohydrates are fructans, which are produced by about 15% of flowering plant species (Hendry, 1993). Fructans are fructose-based oligo- and polysaccharides derived from sucrose by the action of fructosyltransferases, which evolved from vacuolar invertases (VIs) (Van den Ende et al, 2011). When challenged with high sucrose, plant VIs are able to synthesize the fructan trisaccharides 1-kestotriose, 6kestotriose and 6G-kestotriose with a typical 1-kestotriose >6Gkestotriose >6-kestotriose ratio (De Coninck et al, 2005). Plant inulintype fructans are produced by the combined action of sucrose: sucrose 1-fructosyl transferase (1-SST) and fructan: fructan 1fructosyl transferase (1-FFT) (Van den Ende, 2013). All these enzymes belong to family GH32, in which structure-function relationships have been thoroughly investigated (Van den Ende et al, 2009)
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