Metabolomics as a tool to evaluate nut quality and safety

Nuts are important food sources for human nutrition and have health benefits. The chemical compositions of nuts vary based on diverse factors stemming from the preharvest to postharvest stages, which may affect the nutritional quality and safety of nuts. Metabolomics is a powerful tool to investigate these traits by measuring the chemical profiles and their dynamic changes in organisms. With this merit, metabolomics has been increasingly applied in nut research for quality and safety management. This review focuses on recent progress in the evaluation of the quality and safety of nuts (ground and tree nuts) using metabolomics approaches. Preharvest and postharvest factors influencing the chemical profiles and qualitative traits of nuts are presented, and related metabolomics studies are provided. Recent research on multi-omics (metabolomics with other omics approaches) regarding this topic is also provided and discussed. Information on variations in nut metabolites and metabolic networks by preharvest and postharvest factors was organized and presented. Some discriminant metabolites were found to be used as potential biomarkers reflecting nut quality and safety at the pre- and/or postharvest stages. In the preharvest stages, alterations in carbohydrates, amino acids, lipids, and phenolics have been primarily observed, and for postharvest stages, changes in volatile and fatty acid profiles (e.g., lipid oxidation) have been mainly studied and discovered. Based on the current research progress, two future directions (validation of biomarkers and use of multi-omics) that could provide a more accurate and deeper understanding of nut quality and safety were highlighted.