High-Resolution Mass Spectrometry-Based Untargeted Metabolite Profiling of Raisins

Abstract

Raisins (Vitis vinifera L.) are widely consumed nutrient-rich dried fruits and important sources of health-promoting phytochemicals. However, comprehensive information on metabolite alterations associated with varietal differences and biotic stress, particularly mealybug infestation, remains limited. Therefore, this study aimed to characterize and compare the metabolomic profiles of healthy and naturally mealybug-infested raisins from two commercially important grape cultivars, ‘Thompson Seedless’ and ‘Manik Chaman’, and to identify metabolites associated with cultivar characteristics and stress responses. We extracted metabolites using acidified methanol and analyzed them by high-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (HPLC–QTOF–MS) in positive ionization mode. Untargeted metabolomics analysis putatively identified 23 metabolites across diverse chemical classes, including phenolic acids, flavonols, amino acid derivatives, fatty acids, hydroxycinnamic acid glucosides, flavanones, volatile compounds, and lysine derivatives. Distinct cultivar- and infestation-dependent metabolic variations were observed. Healthy raisins exhibited relatively higher levels of flavonols, hydroxycinnamic acid derivatives, and aroma-associated volatile compounds, whereas infested raisins showed accumulation of stress-responsive metabolites, including L-pipecolic acid, proline, hydroxy fatty acids, and branched-chain amino acid derivatives. ‘Thompson Seedless’ demonstrated greater metabolic plasticity, characterized by enhanced accumulation of defense-associated metabolites, whereas ‘Manik Chaman’ exhibited pronounced depletion of phenolic and flavonoid compounds following mealybug infestation. Overall, the findings demonstrate the utility of HRMS-based untargeted metabolomics for comprehensive characterization of raisin metabolites and identification of potential biomarkers associated with cultivar discrimination and biotic stress responses. These metabolic signatures may improve raisin quality assessment, stress-management strategies, and grape breeding programs. To the best of our knowledge, this is the first study to investigate metabolomics profiling in naturally mealybug-infested ‘Manik Chaman’ raisins, using an untargeted HPLC-QTOF-MS approach.