Spatial metabolomic mapping reveals peel-color- and tissue-region-associated metabolic heterogeneity in postharvest 'Yanzhihong' apricot fruit.

INTRODUCTION

Spatial metabolic heterogeneity associated with fruit color and tissue type remains insufficiently characterized in postharvest apricot fruit. In this study, MALDI-MSI-based spatial metabolomics was used to characterize color- and tissue-associated ion-response heterogeneity in postharvest 'Yanzhihong' apricot fruit.

METHODS

RMS-normalized ion responses were analyzed using spatial shrunken-centroid segmentation, principal component analysis (PCA), exploratory orthogonal partial least-squares discriminant analysis (OPLS-DA), fold-change analysis, and sample-level Pearson correlation assessment.

RESULTS

Clear overall differentiation was observed between the red- and yellow-colored sides, indicating color-associated spatial metabolic heterogeneity within the fruit. Exploratory differential-feature screening and subsequent spatial analyses highlighted candidate ion features related to monolignol/phenylpropanoid metabolism, phenolic acids, flavonols, sugar phosphates, nucleotide sugars, and membrane lipids. Candidate ion features tentatively assigned to caffeyl alcohol, 4-hydroxycinnamic acid, and dihydroferulic acid, together with most selected membrane-lipid-related candidate features, showed stronger relative responses on the yellow-colored side. In contrast, candidate ion features tentatively assigned to myricetin-3-O-(4″-acetyl)rhamnoside and UDP-GalNAcA showed stronger relative responses on the red-colored side. Among the selected monolignol/phenylpropanoid-, phenolic-acid-, and flavonol-related candidate ion features, the 4-hydroxycinnamic-acid-related ion was the only feature that showed the same regional ordering on both fruit sides, with lower mean responses in the flesh than in the peel and near-stone regions. Other regional mean differences were feature dependent and were not statistically validated at the current sample size.

DISCUSSION: These findings characterize candidate color- and tissue-associated ion-response features under the sampled postharvest condition. Given the single cultivar, three paired biological replicates, and one postharvest sampling point, the findings remain exploratory and do not establish postharvest-quality markers.