Exogenous Ergothioneine and Glutathione Limit Postharvest Senescence of Arugula

Abstract

Arugula is susceptible to postharvest deterioration. We tested the impact of exogenous antioxidant (i.e., ergothioneine and glutathione) dip solutions on arugula quality during storage at 4 °C or 10 °C for up to 17 days relative to a non-antioxidant treatment. Leaves from each dip treatment and storage temperature were assessed for visual quality and endogenous antioxidant metabolite profiles. Overall, leaf discolouration, wilting, and decay were more rapid at 10 °C than at 4 °C. Both antioxidant treatments limited leaf discolouration at 4 °C. Exogenous ergothioneine reduced wilting at 4 °C, whereas exogenous glutathione limited the incidence of leaf decay. At 10 °C, glutathione reduced the incidence of discolouration and decay, whereas both antioxidant dip treatments limited the decline in leaf yellowing. Ergothioneine was solely detected in ergothioneine-treated leaves; a decrease occurred within the first two days of storage but was unchanged thereafter. Although both antioxidant treatments did not affect endogenous glutathione concentrations at either storage temperature, glutathione disulfide was stable within the glutathione-treated leaves, whereas it increased in the other treatments. Ascorbate degradation was delayed in ergothioneine-treated leaves at 4 °C relative to all other treatments, whereas both antioxidant treatments little affected ascorbate metabolism in leaves stored at 10 °C.

Keywords: arugula; ascorbate; ergothioneine; glutathione; postharvest; senescence.

Figure 1

The incidence of discolouration, wilting, and decay in arugula immersed in a pre-storage dip containing either 100 μM ergothioneine (EGT), 500 μM glutathione (GSH), or no antioxidant, and then stored at 4 °C (A) or 10 °C (B). Each datum represents the mean incidence ± SE of three experimental replicates. Within each plot, uppercase letters denote statistical comparisons within a treatment across the storage period; lowercase letters denote statistical comparisons across the treatments at each postharvest sampling time. Shared letters represent no significant difference between means at p ≤ 0.05.

Figure 2

Leaf chroma, hue angle, and lightness in arugula that was immersed in a pre-storage dip containing either 100 μM ergothioneine (EGT), 500 μM glutathione (GSH), or no antioxidant, and then stored at 4 °C (A) or 10 °C (B). Each datum represents the mean ± SE of three experimental replicates. Within each plot, uppercase letters denote statistical comparisons within a treatment across the storage period; lowercase letters denote statistical comparisons across the treatments at each postharvest sampling time. Shared letters represent no significant difference between means at p ≤ 0.05.

Figure 3

Browning index of arugula immersed in a pre-storage dip containing either 100 μM ergothioneine (EGT), 500 μM glutathione (GSH), or no antioxidant, and then stored at 4 °C or 10 °C. Each datum represents the mean ± SE of three experimental replicates. Within each plot, uppercase letters denote statistical comparisons within a treatment across the storage period; lowercase letters denote statistical comparisons across the treatments at each postharvest sampling time. Shared letters represent no significant difference between means at p ≤ 0.05.

Figure 4

Total chlorophyll in arugula immersed in a pre-storage dip containing either 100 μM ergothioneine (EGT), 500 μM glutathione (GSH), or no antioxidant, and then stored at 4 °C or 10 °C. All total chlorophyll concentrations are expressed on a fresh weight (FW) basis. Each datum represents the mean ± SE of three experimental replicates. Within each plot, uppercase letters denote statistical comparisons within a treatment across the storage period; lowercase letters denote statistical comparisons across the treatments at each postharvest sampling time. Shared letters represent no significant difference between means at p ≤ 0.05.

Figure 5

Ergothioneine (EGT) in arugula immersed in a pre-storage dip containing either 100 μM EGT, 500 μM glutathione (GSH), or no antioxidant, and then stored at 4 °C or 10 °C. (A) HPLC–DAD analysis of EGT in extracts prepared from arugula leaves sampled on day 0 of 4 °C storage and within 2 h of their exposure to dip solutions. Chromatograms represent arugula leaves treated with 100 µM EGT prior to storage (top chromatogram); arugula leaves treated with 100 µM EGT prior to storage, and the extract spiked with 3 nmol EGT at the point of HPLC analysis (second chromatogram from top); arugula leaves treated with 500 µM GSH prior to storage (third chromatogram from top); and arugula leaves not treated with antioxidants prior to storage (bottom chromatogram). (B) Alterations in EGT concentrations in arugula leaves as a function of storage period at 4 °C or 10 °C after a pre-storage dip treatment with or without antioxidants. All EGT concentrations are expressed on a fresh weight (FW) basis. Each datum represents the mean ± SE of three experimental replicates. Within each plot, uppercase letters denote statistical comparisons within a treatment across the storage period; lowercase letters denote statistical comparisons across the treatments at each postharvest sampling time. Shared letters represent no significant difference between means at p ≤ 0.05.

Figure 6

Glutathione profiles (glutathione, GSH; glutathione disulfide, GSSG; and GSH/GSSG ratio) in arugula immersed in a pre-storage dip containing either 100 μM ergothioneine (EGT), 500 μM glutathione (GSH), or no antioxidant, and then stored at 4 °C (A) or 10 °C (B). All glutathione metabolite concentrations are expressed on a fresh weight (FW) basis. Each datum represents the mean ± SE of three experimental replicates. Within each plot, uppercase letters denote statistical comparisons within a treatment across the storage period; lowercase letters denote statistical comparisons across the treatments at each postharvest sampling time. Shared letters represent no significant difference between means at p ≤ 0.05. Plots devoid of statistical lettering represent no significant differences across treatments or their sampling days.

Figure 7

Ascorbate profiles (ascorbate, dehydroascorbate, DHA; and ascorbate/DHA ratio) in arugula immersed in a pre-storage dip containing either 100 μM ergothioneine (EGT), 500 μM glutathione (GSH), or no antioxidant, and then stored at 4 °C (A) or 10 °C (B). All ascorbate metabolite concentrations are expressed on a fresh weight (FW) basis. Each datum represents the mean ± SE of three experimental replicates. Within each plot, uppercase letters denote statistical comparisons within a treatment across the storage period; lowercase letters denote statistical comparisons across the treatments at each postharvest sampling time. Shared letters represent no significant difference between means at p ≤ 0.05.