Abstract
African eggplants (Solanum aethiopicum L.) are a rich source of bioactive compounds and functional constituents that are beneficial to human health. However, the short shelf life of these vegetables can be a major cause of postharvest losses especially during peak harvesting season. Drying is one of the most convenient technologies for the production of shelf stable food products. However, drying can lead to considerable loss of the available bioactive compounds due to thermal degradation depending on the drying method and temperature conditions. This study investigated the effect of four drying methods (solar, oven, vacuum, and freeze) on the retention of total phenolics, beta‐carotene, antioxidant capacity, and lycopene in five African eggplant (S. aethiopicum) accessions (sangawili, manyire green, S00047A, AB2, and aubergine blanche). Samples were dried up to ~10% moisture content. The fresh and dried samples were analyzed for total phenolic content, antioxidant capacity, beta‐carotene content, and the lycopene content. In the fresh state, beta‐carotene, total phenolic content, and free radical scavenging activity ranged between 14.75 ± 0.50 and 29.50 ± 0.77 mg/100 g db, 751.21 ± 1.73 and 1,363.95 ± 2.56 mg/100 g GAE db, and 99.58 and 325.61 mg/ml db IC 50 value, respectively. The accession S00047 showed highest total phenolic content and lowest IC 50 value in the fresh samples. The results also showed that total phenolic content, antioxidant capacity, and beta‐carotene contents were significantly (p < .05) affected by drying method and drying temperature with freeze‐drying presenting the highest retention. Overall, 36.26%s–95.05% (total phenolics) and 31.44%–99.27% (beta‐carotene) were retained during freeze‐drying. Lycopene was only detected in the dried samples of the accession manyire green but absent in all the fresh samples of all the accessions. This study demonstrates that freeze‐drying was the most effective in retaining the highest bioactive compounds in African eggplants.
Highlights
Bioactive compounds comprise of vitamins, carotenoids, flavonoids, and other phenolic compounds which are found in fruits and vegetables in appreciable amounts (Minussi et al, 2003; Zhang & Hamauzu, 2004)
The results of this study indicate that the five African eggplant accessions are high in bioactive compounds as exhibited by high total phenolic content in particular
The total phenolic content of the five accessions in fresh samples is of similar range in different Turkish eggplant (S. melongena) cultivars reported by Okmen et al (2009) and Hanson et al (2006)
Summary
Bioactive compounds comprise of vitamins, carotenoids, flavonoids, and other phenolic compounds which are found in fruits and vegetables in appreciable amounts (Minussi et al, 2003; Zhang & Hamauzu, 2004) These phytochemical components are high in antioxidant and antiradical activities that are responsible for reducing the risk of radical-mediated pathogenesis such as carcinogenesis, atherosclerosis, diabetes, Alzheimer, cataracts, and age-related functional decline (Atoui, Mansouri, Boskou, & Kefalas, 2005; Stommel & Whitaker, 2003; Zhang & Hamauzu, 2004). African eggplants known as the scarlet eggplant are wild relatives of the common eggplant (Solanum melongena) (Schippers, 2000) They belong to the Solanum genus and comprise of cultivated species such as the Gboma eggplant (Solanum macrocarpon L.), the scarlet eggplant (Solanum aethiopicum L.), and Solanum anguivi, which are grown mostly in Africa for their fruits and leaves. Aculeatum group is utilized as an ornamental as well as a rootstock (Daunay, 2008; Lester & Daunay, 2003; Schippers, 2000)
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