Fructans and Fructooligosaccharides in Plants and Fruits: Metabolism, Functional Roles, and Emerging Biotechnological Opportunities

Fructans and fructooligosaccharides (FOSs) are structurally diverse fructose-based carbohydrates synthesized from sucrose through the coordinated action of fructosyltransferases. These compounds are widely distributed in plants and have attracted increasing attention due to their dual relevance in plant physiology and human nutrition. In plants, fructans function as dynamic carbon reserves and play key roles in tolerance to abiotic stresses such as drought, cold, and salinity. In parallel, their selective fermentability and prebiotic properties have positioned them as valuable functional ingredients in food and nutraceutical applications. This review provides an updated overview of fructan and FOS metabolism, focusing on their biosynthetic pathways, structural diversity, and physiological roles in plants. Particular attention is given to the occurrence and potential functions of fructans in fruits, a topic that remains comparatively underexplored. We also discuss recent advances in strategies aimed at enhancing fructan accumulation through breeding, metabolic engineering, and synthetic biology approaches. Finally, emerging opportunities for the biotechnological exploitation of fructan metabolism are highlighted, including crop biofortification, development of functional foods, and the improvement of plant resilience to environmental stress.