New Insights into Sprout Production from Melon (Cucumis melo L. var. reticulatus) Seeds as By-Product of Fruit Processing

Abstract

Melon is a valuable crop that generates significant by-products during consumption and processing. Among these, seeds are rich in phenolic compounds and might be used to produce sprouts with increased content of these bioactive substances. This study evaluated phenolic compounds (PhCs) in sprouts of two melon cultivars, Thales and SV9424ML, obtained from seeds having different germination speeds, thus harvested at 6 and 14 days after sowing (DAS). A factorial combination of cultivar and harvest time was tested in a completely randomized design with four replicates. Thales produced more ready-to-eat sprouts at 6 DAS than SV9424ML (64.0% vs. 46.7%). Sprouting significantly increased total PhCs content, particularly flavonoids, with Thales showing higher values than SV9424ML (50.2 vs. 32.6 mg kg^-1 DW). Phenolic profiles significantly varied among cultivars and harvests. Sprouts at 6 DAS had more total hydroxybenzoic acids and flavonoids, while 14 DAS sprouts were richer in hydroxycinnamic acids. Significant differences between harvest dates were observed in the concentrations of protocatechuic, vanillic (VanA), p-coumaric (p-CouA), ferulic (FerA) acids, and orientin (Ori) for Thales, and of VanA, p-CouA, FerA, and Ori for SV9424ML. Results are encouraging, but future investigations are essential to understand whether these sprouts can be suitable for fresh consumption, food supplements, or phytochemical extraction.

Keywords: flavonoids; germination; hydroxybenzoic acids; hydroxycinnamic acids; polyphenol.

Figure 1

Percentage of sprouts of two melon cultivars (Thales and SV9424ML) harvested at (a) 6 and (b) 14 days after sowing (DAS), and (c) overall. On each date, only sprouts that had reached the ready-to-eat stage (fully expanded cotyledons) were sampled; further details are provided in the text. Data represent means ± standard errors, n = 4 independent replicates.

Figure 2

Total Phenolic Compounds (as the sum of all the detected phenolic acids and flavonoids; mg kg⁻¹ dry weight, DW) as observed in seeds and sprouts of two melon cultivars (CV; Thales and SV9424ML). Sprouts at the ready-to-eat stage were harvested at two different dates (Harvest; 6 and 14 days after sowing, DAS); further details are provided in the text. Bars represent the standard errors of the differences between means (s.e.d.) of the interaction CV × Harvest. In the boxes, the results of the two-way ANOVA (degrees of freedom: CV, 1; Harvest, 2; CV × Harvest, 2; residues, 18): ** p < 0.01); numbers in the brackets represent the s.e.d. Different letters indicate significant differences of the interaction CV × Harvest at p < 0.05 (Fisher’s Least Significant Difference, LSD).

Figure 3

Phenolic compounds (mg kg⁻¹ dry weight, DW) as observed in seeds and sprouts of two melon cultivars (CV; Thales and SV9424ML). Sprouts at the ready-to-eat stage were harvested at two different dates (Harvest; 6 and 14 days after sowing, DAS); further details are provided in the text. (a) Total hydroxybenzoic acids (as the sum of 4-hydroxybenzoic acid, protocatechuic acid, gallic acid, vanillic acid, syringic acid); (b) total hydroxycinnamic acid (as the sum of caffeic acid, chlorogenic acid, p-coumaric acid, ferulic acid, trans-cinnamic acid); (c) total flavonoids (as the sum of apigenin, luteolin, diosmetin, orientin, rutin, myricetin, naringenin). Bars represent the standard errors of the differences between means (s.e.d.) of the interaction CV × Harvest. In the boxes, the results of the two-way ANOVA (degrees of freedom: CV, 1; Harvest, 2; CV × Harvest, 2; residues, 18): ** p < 0.01); numbers in the brackets represent the s.e.d. Different letters indicate significant differences of the interaction CV × Harvest at p < 0.05 (Fisher’s Least Significant Difference, LSD).