Untargeted multi-platform analysis of the metabolome and the non-starch polysaccharides of kiwifruit during postharvest ripening
The popularity of kiwifruit (Actinidia deliciosa) is steadily rising among consumers since their introduction in the global market 60 years ago. Kiwifruit are ripened postharvest for marketing. A good technique to follow the complex changes throughout postharvest ripening is metabolomics. So far research on the kiwifruit metabolome has been performed on kiwifruit development or on-vine ripening. This study aimed at a comprehensive description of processes during postharvest ripening of kiwifruit. Metabolic changes in kiwifruit during six well-defined stages of postharvest ripening and two non-marketable stages due to water loss were monitored using an untargeted multi-platform approach consisting of GC × GC–MS, GC–MS and NMR. In addition, postharvest cell wall polysaccharide modifications were followed using multiple chromatographic approaches. Using the multi-platform approach, it was possible to follow the process of postharvest ripening kiwifruit. Investigation of soluble metabolites in kiwifruit yielded mainly sugars, sugar-related substances and organic acids as well as other known and unknown metabolites. Sugars predominantly increased during ripening while organic acids predominantly decreased. In addition, unexpected changes in the concentration of some known and unknown metabolites were observed. Changes of the non-starch polysaccharides were dominated by a continuous loss of neutral pectic side chains, whereas minor changes were observed for homogalacturonan and hemicellulosic polysaccharides only. Overall the three applied platforms and the cell wall characterization were complementary and allowed a comprehensive description of the kiwifruit metabolome during postharvest ripening.