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Extraction Efficiency of Solvents and Postharvest Effects on Melon (Cucumis Melo L.) Health-Promoting Compounds Measured Using HPLC and HS-SPME-GC-MS
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Melons (Cucumis melo) have abundant health-promoting phytochemicals; understanding how these change during postharvest storage provides important information for preserving these phytochemicals. Here, we tested three cantaloupe cultivars (Western Shipper, Infinite Gold, and Da Vinci) and three honeydew varieties (Orange Casaba, HD150, and HD252) grown in Uvalde, Texas. Fruits were stored at 10 C for 20 days, processed and analyzed at 5-day intervals for carotenoids, amino acids and ascorbic acid using HPLC. Da Vinci showed high levels of β-carotene (24.27±0.88 mg kg-1) on day 0 of storage. Total ascorbic acid was highest in Western Shipper and Da Vinci melons on day 0 (112.82±13.96 mg kg-1, 90.39 ±14.43 mg kg-1) and decreased at day 20 (17.67±1.88 mg kg-1, 31.33 ±3.88 mg kg-1). Honeydew variety HD252 showed the highest total ascorbic acid at day 5 (70.94±3.50 mg kg-1) and this decreased (31.53 ±3.54 mg kg-1) at the end of storage (day 20). The important neurotransmitter GABA was highest in Da Vinci cantaloupes at day 0 (2985.04±79.17 µg g-1) and decreased (2426.89±102.57 µg g-1) at day 20. The total amino acid levels changed during storage, showing an overall increase at day 20. Da Vinci and Infinite Gold varieties showed high total amino acid contents on day 0 (8050.27±390.64 mg kg-1, 7809.86±399.82 mg kg-1), which increased on day 20 (9495.72±640.85 mg kg-1, 8473.21±358.24 mg kg-1). Interestingly, the biogenic amines putrescine and spermidine were observed during storage. Total phenolics content (TPC) showed different trends in each variety; for example, on day 0 da Vinci showed high TPC (21.81±0.70 g L-1), Western Shipper showed high TPC on day 5 (19.32±1.21 g L-1), HD150 showed high TPC on day 15 (19.53±0.85 g L-1) and HD252 showed high TPC (18.87±1.20 g L-1) on day 20. The aroma profile of each variety was analyzed using HS-SPME-GC-MS and identified compounds were classified as alcohols, aldehydes, esters, monoterpenoids (limonene, α-terpineol, 1,8 cineole, citronellal), and norisoprenoid (β-ionone). During postharvest storage, melon fruits showed significant variation in phytonutrients, free radical scavenging activity, and aroma profiles. These results indicate that the postharvest changes in bioactive compounds are influenced by melon variety and storage duration. This study compared the effect of 22 solvent combinations using different ratios of methanol, ethanol, acetone, water, and formic acid on TPC and free radical scavenging activity in melons obtained from College Station, Texas. TPC was determined using the Folin-Ciocalteu (F-C) assay and an optimized Fast Blue (FB) assay. The FB assay showed that water extracted the highest TPC (94.82±8.02 mg kg-1 gallic acid equivalents, GAE). The F-C assay showed that methanol extracted the highest TPC (137.99±18.29 mg kg-1 GAE), indicating that the FB assay was more sensitive for water extracts. Free radical scavenging activity was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. The DPPH scavenging activities were high in methanol (100%) (38.49±0.36 mg kg-1 ascorbic acid equivalents, AAE) and 80% methanol extracts (38.99±0.44 mg kg-1 AAE). Similarly, the ABTS scavenging activities were high in methanol (100%) (315.11±10.38 mg kg-1 AAE) and 80% methanol extracts (297.39±14.98 mg kg-1 AAE). Generally, the results indicated that the solvent used affected TPC and free radical scavenging activities. Moreover, we successfully detected six phenolic compounds in melon extracts by liquid chromatography coupled with high resolution quadrupole time-of-flight mass spectrometry. Our results suggest that the polarity of the solvent used to extract the melon samples influenced the recovery of phenolic compounds and free radical scavenging activity.
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Ravindranath, Varsha (2020). Extraction Efficiency of Solvents and Postharvest Effects on Melon (Cucumis Melo L.) Health-Promoting Compounds Measured Using HPLC and HS-SPME-GC-MS. Master's thesis, Texas A&M University. Available electronically from