Biochemical monitoring of black raspberry (Rubus coreanus Miquel) fruits according to maturation stage by 1H NMR using multiple solvent systems

Nuclear magnetic resonance (NMR) techniques coupled with multivariate data analysis were used to conduct monitoring of biochemical changes of black raspberry fruits at different stages of maturation and under various extraction and NMR dissolution solvent conditions: extraction with 50 methanol and D2O as an NMR dissolution solvent, extraction with 50 methanol and 50 methanol-d4 as an NMR dissolution solvent, and extraction with 100 ethyl acetate and 100 methanol-d4 as an NMR dissolution solvent. Partial least-squares discriminant analysis reliably distinguished black raspberry fruits according to the maturation stage, whereby the relative levels of various compounds such as amino acids, organic acids, sugars and phenolic compounds were compared using analysis of variance. Sucrose and most of the amino acids, and organic acids decreased, whereas fructose, glucose, and cyanidins increased in relative concentration according to maturation of black raspberry fruits. The total number and kinds of assigned compounds of the three solvent systems were also compared. This research demonstrates that the metabolic profile of black raspberry fruits changes during maturation, and provides objective criteria for determining the stage of black raspberry fruit maturation via a 1H NMR-based metabolomics technique using multiple solvent systems.