Monitoring metabolic changes during storage of hazelnuts (Corylus avellana L.) by 1H NMR spectroscopy

Storage is a critical step in post-harvest processing of hazelnuts since it can lead to mold, rancidity and off-flavor. To comprehensively investigate the effects of hazelnut storage, samples were stored under three short-term and two long-term conditions and the polar metabolome was analyzed by 1H NMR spectroscopy at different time points. Large differences in the polar metabolome were observed between the investigated storage conditions. Classification between samples before and after storage showed that samples stored under harsh conditions for a short-term and under standard conditions for a long-term were almost always classified correctly. Boruta, a feature selection algorithm, was used to identify which metabolites were significant for classification. Increases in hexanoic octanoic and nonanoic acid, all products of lipid oxidation, were found across all conditions and an increase in formic acid in most. Harsh short-term storage resulted in an increase in fumaric and lactic acid, glucose, fructose, and choline and a decrease in acetic acid.