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. 2022 Apr 18;11(8):1174.
doi: 10.3390/foods11081174.

Metabolomic Analysis, Combined with Enzymatic and Transcriptome Assays, to Reveal the Browning Resistance Mechanism of Fresh-Cut Eggplant

Xiaohui Liu  1   2 , Kai Xiao  1 , Aidong Zhang  1 , Weimin Zhu  1 , Hui Zhang  1 , Feng Tan  1 , Qianru Huang  1 , Xuexia Wu  1 , Dingshi Zha  1
Affiliations

Metabolomic Analysis, Combined with Enzymatic and Transcriptome Assays, to Reveal the Browning Resistance Mechanism of Fresh-Cut Eggplant

Xiaohui Liu et al. Foods. .

Abstract

Browning has been the primary limitation in eggplant processing. This study investigates the molecular mechanism underlying fresh-cut eggplant fruit browning by observing the physicochemical characteristics of browning-resistant ('F') and browning-sensitive ('36') eggplant cultivars. Browning-related enzyme activity and gene expression (PPO, LOX, and PLD) were significantly higher in the '36' eggplant, thereby enhancing the degree of browning, compared to the 'F' eggplant. The MDA content and O2- production rate progressively increased as browning increased, while the antioxidant capacity of the fruit decreased. The cutting injury significantly activated the expression of PAL, thereby inducing the accumulation of phenolic acids, while the PPO gene was significantly upregulated, which activated the activity of polyphenol oxidase. Our results showed that the oxidation of chlorogenic acids to chlorogenic quinones resulted in the occurrence of browning, which suggests chlorogenic acid as the main browning substrate in fresh-cut eggplant.

Keywords: Solanum melongena; browning; membrane lipid metabolism; metabolome; transcriptome.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Browning phenotype of slices (a) and browning degree (b) of browning-sensitive (‘36′) and browning-resistant (‘F’) cultivars after cutting.
Figure 2
Figure 2
KEGG analysis of the DEMs in (a) F CK0/36 CK0; (b) F 2 min/36 2 min; and (c) F 15 min/36 15 min. Note: The ordinate refers to metabolic pathway; abscissa is the enrichment factor (Enrichment factor = the number of metabolites with significant difference/the number of total metabolites in the pathway). The color change from red to green means that the p-value increases successively.
Figure 3
Figure 3
Heat map of membrane lipid content difference of fresh-cut eggplant in F 15 min/36 15 min. Note: Hierarchical clustering of DEMs (p < 0.05 and VIP > 1 were considered as DEMs between two groups). The rows in the heat map represent metabolites, and the columns represent different samples. Up-regulated metabolites are indicated in red and down-regulated metabolites in green.
Figure 4
Figure 4
Changes in fresh-cut eggplant fatty acid composition and content. (a) Oleic acid relative content; (b) linoleic acid relative content; (c) linolenic acid relative content; (d) palmitic acid relative content; (e) stearic acid relative content; and (f) ratio of unsaturated to saturated fatty acids, U/S. Note: The means ± SE of six replicates are shown. Different letters above the bars indicate the statistically significant difference at p < 0.05.
Figure 5
Figure 5
The DEGs and DEMs involved in LA, AA, and ALA metabolism in response to browning. The green pattern represented the genes that changed after cutting. Note: The rectangle was divided into three equal parts representing DEGs or DEMs in F CK0/36 CK0, F 2 min/36 2 min, and F 15 min/36 15 min, respectively. Red represents up-regulation and blue represents down-regulation.
Figure 6
Figure 6
The DEGs and DEMs of Phenylpropanoids biosynthesis during fresh-cut. Note: The green pattern represented the genes that changed after cutting. The rectangle was divided into three equal parts representing DEGs or DEMs in 36 CK0/F CK0, 36 2 min/F 2 min, and 36 15 min/F 15 min, respectively. Red represents up-regulation and blue represents down-regulation.
Figure 7
Figure 7
The DEGs and DEMs of ASA–GSH metabolism during fresh-cut eggplant browning. Note: The green pattern represented the genes that changed after cutting. The rectangle was divided into three equal parts representing DEGs or DEMs in F CK0/36 CK0, F 2 min/36 2 min, and F 15 min/36 15 min, respectively. Red represents up-regulation, and blue represents down-regulation.
Figure 8
Figure 8
The MDA content (a), H2O2 content (b), and O2− production rate (c) of eggplant fruit after cutting.
Figure 9
Figure 9
The PPO activity (a), POD activity (b), LOX activity (c), PLD activity (d), PAL activity (e), and TP content (f) of eggplant fruit after cutting.
Figure 10
Figure 10
DPPH radical scavenging ability (a), ABTS radical scavenging activity (b), FRAP scavenging ability (c), CAT activity (d), SOD activity (e), and APX activity (f) of eggplant fruit after cutting.
Figure 10
Figure 10
DPPH radical scavenging ability (a), ABTS radical scavenging activity (b), FRAP scavenging ability (c), CAT activity (d), SOD activity (e), and APX activity (f) of eggplant fruit after cutting.
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