Peaches and nectarines [Prunus persica (L.) Batsch] are among the most exported fresh fruit from Chile to the Northern Hemisphere. Fruit acceptance by final consumers is defined by quality parameters such as the size, weight, taste, aroma, color, and juiciness of the fruit. In peaches and nectarines, the balance between soluble sugars present in the mesocarp and the predominant organic acids determines the taste. Biomass production and metabolite accumulation by fruits occur during the different developmental stages and depend on photosynthesis and carbon export by source leaves. Carbon supply to fruit can be potentiated through the field practice of thinning (removal of flowers and young fruit), leading to a change in the source–sink balance favoring fruit development. Thinning leads to fruit with increased size, but it is not known how this practice could influence fruit quality in terms of individual metabolite composition. In this work, we analyzed soluble metabolite profiles of nectarine fruit cv “Magique” at different developmental stages and from trees subjected to different thinning treatments. Mesocarp metabolites were analyzed throughout fruit development until harvest during two consecutive harvest seasons. Major polar compounds such as soluble sugars, amino acids, organic acids, and some secondary metabolites were measured by quantitative ¹H-NMR profiling in the first season and GC-MS profiling in the second season. In addition, harvest and ripening quality parameters such as fruit weight, firmness, and acidity were determined. Our results indicated that thinning (i.e., source–sink imbalance) mainly affects fruit metabolic composition at early developmental stages. Metabolomic data revealed that sugar, organic acid, and phenylpropanoid pathway intermediates at early stages of development can be used to segregate fruits impacted by the change in source–sink balance. In conclusion, we suggest that the metabolite profile at early stages of development could be a metabolic predictor of final fruit quality in nectarines.

The agro-industrial sector generates large volumes of fruit waste each year, leading to environmental concerns and sustainability challenges. In this study, we evaluate the potential of fruit residues—apple, pear, blueberry, tomato, papaya, and a mixed fruit juice blend—as alternative sources of high-value polysaccharides, including pectins, hemicelluloses, and cellulose. Additionally, white strawberry, included as a reference from fresh fruit rather than agro-industrial waste, was analyzed to expand the comparative framework. These biopolymers, naturally derived from the plant cell wall, are renewable and biodegradable, and they possess physicochemical properties suitable for applications in food, pharmaceutical, cosmetic, textile, and bioenergy industries. Using a combination of cell wall fractionation, biochemical characterization, and immunodetection of specific structural domains, we identified significant variability in polysaccharide composition and structure among the samples. Blueberry, pear, and apple residues showed high levels of rhamnogalacturonan-I (RG-I) with extensive branching, while variations in rhamnogalacturonan-II (RG-II) dimerization and the degree of methylesterification of homogalacturonan were also observed. These structural differences are key to determining the gelling properties and functional potential of pectins. In the hemicellulose fractions, xylans and xyloglucans with distinct substitution patterns were especially abundant in apple and pear waste. Our findings demonstrate that fruit processing waste holds significant promise as a sustainable source of structurally diverse polysaccharides. These results support the reintegration of agro-industrial residues into production chains and emphasize the need for environmentally friendly extraction methods to enable industrial recovery and application. Overall, this study contributes to advancing a circular bioeconomy by transforming underutilized plant waste into valuable functional materials.

Background: Peach fruit quality can be compromised by cold storage, a postharvest practice required for long-distance export that can trigger chilling injury and metabolic disturbances affecting sugars, organic acids, and other metabolites. Preharvest practices such as thinning modify source–sink relationships and fruit development, potentially influencing susceptibility to chilling stress. Objectives: This study aimed to determine whether commercial thinning alters fruit susceptibility to cold storage damage and to identify metabolic processes associated with chilling tolerance in two nectarine varieties with contrasting sensitivity, ‘Magique’ (tolerant) and ‘Red Pearl’ (sensitive). Methods: Fruits from thinned (TH) and unthinned (UTH) trees were subjected to cold storage (0 °C, 21 days) followed by ripening, and evaluated for physiological parameters, sugar and organic acid composition by HPLC, and phenylpropanoid-related metabolites by ¹H-NMR. A genome-scale metabolic model was built to model fruit metabolism using COBRApy. Results: Thinning increased fruit size in both varieties. Magique exhibited overall metabolic stability across thinning treatments and cold storage. Red Pearl, in contrast, showed broad metabolic fluctuation in response to external stimuli. Integration of transcriptomic data and metabolic modeling identified quinate-centered reactions as candidate regulatory nodes associated with phenylpropanoid flux during ripening and post-chilling recovery. Conclusions: These findings indicate that modulating quinate metabolism during early ripening may help improve chilling tolerance and highlight the phenylpropanoid pathway as a central metabolic axis modulated by both pre- and postharvest practices, with implications for fruit quality management.

Lipoic acid (LA) is a potent antioxidant and is also bound as an essential enzymatic cofactor to mitochondrial and plastidial protein complexes, indispensable for all living organisms. In plants, LA biosynthesis requires S-adenosyl-L-methionine (SAM or Ado-Met), which is also the precursor for ethylene production. Tomato (Solanum lycopersicum) fruit maturation is a climacteric process characterized by an autocatalytic rise in ethylene synthesis, increased respiration, and elevated production of reactive oxygen species (ROS), requiring the activation of antioxidant systems. Despite the shared dependence of LA and ethylene biosynthesis on SAM, the interaction between these pathways during fruit maturation remains poorly understood. To address this, fruits from tomato plants subjected to three complementary conditions were analyzed: application of exogenous LA (200 or 500 nM), fruit-specific overexpression of the key enzyme required for LA synthesis, mitochondrial lipoyl synthase (PG:SlLIP1m) to enhance endogenous LA, and inhibition of ethylene biosynthesis using aminoethoxyvinylglycine (AVG). Increased LA levels, achieved either exogenously or genetically, delayed the breaker-to-red transition and significantly increased fruit weight, accompanied by higher bound and free LA pools, greater ethylene levels and enhanced antioxidant capacity at late developmental stages. AVG treatments also delayed maturation and increased LA content, but failed to enhance fruit weight and resulted in reduced antioxidant capacity. LA- and ethylene-enriched fruits displayed altered ethylene dynamics and expression of PG2 and NAP2, whereas AVG treatment reduced expression of both ethylene marker genes, consistent with ethylene inhibition. Collectively, these findings support a more complex interaction between LA and ethylene in regulating tomato fruit maturation through redox and metabolic homeostasis, rather than simple competition for SAM, providing a potential strategy to modulate maturation timing and improve fruit biomass.