LC-MS-MS Analysis and the Antioxidant Activity of Flavonoids from Eggplant Skins Grown in Organic and Conventional Environments

Eggplant (Solanum melongena), or aubergine, is a species of nightshade, grown for its edible fruit. In recent years, its consumption in the American diet has continuously increased due to ever greater cultural diversity and awareness that consumption of fruits and vegetables provides significant health benefits. And it has been known that eggplant fruits contain different classes of phenolic phytochemicals (flavonols, phenolic acids, and anthocyanins) that can exert beneficial effects on human health. While different fruit parts, e.g. skin, pulp and seed, can have different phytochemical profiles, so the authors in this study focused on the eggplant skin polyphenol composition in two popular hybrid varieties, Blackbell and Millionaire.

In this study, Blackbell and Millionaire were grown in Hanford sandy loam soil under both under conventional (Alvarez Farm) in Reedley, California and organic (T&D Willey Farm) in Madera, California. Eggplant fruits were harvested, placed immediately in ice chest, and sent overnight in refrigeration to the Food Composition Method Development Laboratory in Beltsville, MD. All samples were peeled to isolate the skins (purple outer peel) from the whitish fleshy pulp of the fruits. Samples were stored in a freezer below −60˚C and freeze-dried. The freeze-dried samples were ground in a coffee grinder and the ground samples were stored below −60˚C until extracted and analyzed. And this study developed methods for the qualitative and quantitative composition analysis of phenolic compounds in the skin of eggplant fruits. Also, eggplant skin was extracted by using aqueous methanol prior to phenolic profiling with UHPLC-ESI-MS-MS.

The results indicated that the analyzed eggplant skin extracts yielded a profile of 16 phenolic acids, 4 anthocyanins, and 11 flavonols, the first report of quercetin-3-diglucoside, myricetin-3-neohesperidoside, myricetin-3-galactoside, kaempferol-3,7-diglucoside, kaempferol-diglucoside and quercetin-3-rhamnoside. Polyphenolic extracts from all sources potently delayed the cupric ion-mediated lag-time for LDL lipid oxidation and protected Apo-B100 proteins against oxidative modification. Organic growing environment positively influenced eggplant skin extract phenolic profile but not antioxidant capacity.

In conclusion, eggplant skin has a robust profile of phenolic phytochemicals with excellent antioxidant properties. And future studies are needed to characterize how to promote the development of eggplant fruits with higher phenolic content and potentially greater human health benefits.

Article by Ajay P. Singh, et al, from USA.

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