Chemical characteristics of non-starch polysaccharides of Opuntia cladodes as evidence of changes through domestication
2018
García Nava, Francisca | López-Herrera, Maritza | Peña Valdivia, Cecilia Beatriz | Romo Gómez, Claudia | Marmolejo Santillán, Yolanda
Our knowledge of the complex domestication process originates from a small subset of crops. Non-starch polysaccharides are abundant in cladodes (“nopalitos”) of the Opuntia genus, which people consume as vegetables. Chemical characteristics of these polysaccharides often respond to the species domestication. In this study, we assess the partial chemical variation of cladode non-starch polysaccharides in Opuntia, in a domestication gradient. For it, we isolated mucilage, pectins, and hemicelluloses. The degree of esterification, methylation and total galacturonic acid for mucilage and pectins were determined. Also, to calculate structural protein content in those polysaccharides the total nitrogen was measured. A completely randomized experimental design was used, including 14 Opuntia variants of five species and six replicates. The degree of mucilage esterification (58.26–69.95%) and pectins (59.43–69.68%), and the degree of methylation of mucilage (25.24–28.66%) were independent of the domestication level. In contrast, the degree of pectins methylation (24.48–27.16%) was higher in wild species than in the domesticated. Total galacturonic acid content in mucilage (1.83–4.10 mMol 100mg−1 dry biomass) and pectins (6.46–10.33 mMol 100mg−1 dry biomass) was higher in domesticated species than in the wild ones. However, the content of structural protein in pectins (2.45–2.9%), loosely bound hemicelluloses (0.21–0.28%) and tightly bound hemicelluloses (0.45–0.79%) was higher in wild species. Chemical characteristics of structural polysaccharides significantly vary with domestication, probably a consequence of selection pressure for wide agricultural environments.
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