Effect of sample pretreatment on the extraction of lemon (Citrus limon) components.

A study on the key role of lemon sample pretreatment on the analytical results is here presented. The objective of the study was to analyze the differences between extracts obtained from lyophilized and air-dried samples-the most common sample pretreatment in citrus studies-in comparison to extracts from fresh samples. All the extracts were obtained with ultrasound assistance and analyzed by LC-QTOF MS/MS. The dataset, constituted by 74 tentative identified metabolites, was first evaluated by ANOVA, which showed significant differences in the concentration of 44 out of 74 metabolites (p≤0.01). Also, the pairwise mean comparison (Tukey HSD; p≤0.01) revealed that the concentration of metabolites in the extracts from fresh and air-dried samples was quite similar and differed from that in lyophilized samples. On the other hand, application of principal component analysis (PCA) showed a clear discrimination between pretreatments, explaining 86.20% of the total variability. The results of this study suggest that the main differences between extracts could be attributed to the effect of freezing or heating on metabolic pathways, and not only to thermolability of the compounds.