Optimizing processing methods for maximum bioactive retention: comparative metabolomic analysis of dried loquat (Eriobotrya japonica) flowers and their powdered extracts

Abstract

Loquat (Eriobotrya japonica) flowers are a rich source of bioactive flavonoids, but their nutraceutical potential depends on post-harvest processing. This study evaluated the impact of heat-drying (HD) and freeze-drying (FD) on flavonoid retention in loquat flowers and their hot-water powdered extracts using UPLC-MS/MS metabolomics and antioxidant assays. Freeze-drying significantly preserved thermolabile compounds, with cyanidin showing a 6.62-fold increase (Log2FC 2.73) in FD compared to HD, while delphinidin 3-O-beta-D-sambubioside surged 49.85-fold (Log2FC 5.64). In contrast, heat-drying degraded many flavonoids but selectively enhanced others, such as 6-hydroxyluteolin (27.36-fold increase, Log2FC 4.77), and methyl hesperidin showed highlest percentage abundance (10.03%). Freeze-dried powder (FDP) exhibited the highest antioxidant activity (608.83 μg TE/g), linked to elevated levels of key metabolites like eriodictyol chalcone (18.62-fold increase, Log2FC 4.22). Multivariate analyses confirmed distinct clustering, with FD samples closely grouped, indicating stable metabolite preservation. Heat-dried samples showed greater variability, reflecting thermal degradation and pathway activation. The results demonstrate that freeze-drying optimizes flavonoid retention, making it ideal for high-quality nutraceuticals, while heat-drying may suit cost-effective production of select heat-stable compounds. These insights guide the development of standardized loquat flower products, balancing bioactive preservation with processing efficiency for functional food and herbal medicine applications.

Keywords: UPLC–MS/MS metabolomics; antioxidant capacity; bioactive flavonoid compound preservation; freeze-drying vs. heat-drying; loquat flower flavonoids powder.

Figure 1

Venn diagrams illustrate shared and unique compounds in loquat flower samples. (A) Comparison of raw sample groups (HD, FD, FS). (B) Comparison of processed sample groups (HDP, FDP, FSP). FS, fresh sample; HD, heat drying; FD, freeze-drying; FSP, fresh sample powder; HDP, heat drying powder; FDP, freeze-drying powder.

Figure 2

Differential metabolite changes in loquat flower samples under varying processing conditions. Column graphs depict the number of upregulated (light blue), downregulated (pale red), and total (light green) compounds in different pairwise comparison groups. Each bar indicates biological replicates (n = 3).

Figure 3

Hierarchical cluster analysis (HCA) of loquat flower metabolites across processing methods. Dendrogram and heatmap display metabolite abundance (row were normalized) in fresh (FS and FSP), heat-dried (HD, HDP), and freeze-dried (FD, FDP) samples. Flavonoid 1–10 names are mentioned in Supplementary Table S2. Color intensity reflects relative concentrations (red: high; blue: low). Clusters highlight distinct metabolite profiles driven by processing. FS, fresh sample; HD, heat drying; FD, freeze-drying; FSP, fresh sample powder; HDP, heat drying powder; FDP, freeze-drying powder.

Figure 4

Principal component analysis (PCA) of loquat flower metabolites across processing methods. (A) Compound-wise PCA (PC1: 71.99%, PC2: 15.43%). FC1-98 names denote individual flavonoid compound represented in Supplementary Table S2. (B) Group-wise PCA (PC1: 57.56%, PC2: 14.14%) highlighting processing-based separation. FS, fresh sample; HD, heat drying; FD, freeze-drying; FSP, fresh sample powder; HDP, heat drying powder; FDP, freeze-drying powder.

Figure 5

Concentration variations of key bioactive metabolites in loquat flowers under different processing methods. Column graphs show relative percentage peak area of eight representative metabolites (violanthin, okanin-4′-acetylglucoside, eupatolitin-3-glucoside, 5,7,2′,5′-tetrahydroxy-8,6′-dimethoxyflavone, methyl hesperidin, cyanidin, 7,4′-dihydroxyflavone, apigenin-7-O-rutinoside, and syringetin) across fresh sample (FS), heat drying (HD), freeze-drying (FD), fresh sample powder (FSP), heat drying powder (HDP), and freeze-drying powder (FDP). Values represent means ± standard deviation (n = 3) generated from LC-MS/MS data. Different lowercase letters indicate significant differences between groups (p < 0.05 by LSD test).

Figure 6

DPPH radical scavenging capacity of differently processed loquat flower samples. Column graph comparing the antioxidant activity expressed as μg Trolox equivalents per gram of fresh samples (FS), heat-dried (HD), freeze-dried (FD) loquat flowers and their corresponding powdered extracts fresh sample powder (FSP), heat drying powder (HDP), and freeze-drying powder (FDP). Values represent means ± standard deviation (n = 3). Different lowercase letters indicate significant differences between groups (p < 0.05 by LSD test).