Influence of conventional and organic agricultural practices on the phenolic content in eggplant pulp: Plant-to-plant variation

Consumer awareness, pesticide and fertiliser contaminations, and environmental concerns have resulted in significant demand for organically grown farm products. The present study evaluates the influence that organic and conventional farming practices exert on the total phenolic content in eggplant samples from two cultivars, Blackbell (American eggplant) and Millionaire (Japanese eggplant), grown by conventional and organic farming practices with similar climatic conditions. In addition, plant-to-plant variation in phenolic content was determined from eight eggplant samples collected from different plants grown at various field positions. Samples were separately assayed for phenolic content by the two independent procedures, HPLC/LC–MS and Folin–Ciocalteu assay. The results of the HPLC analysis showed significant plant-to-plant variation (% RSD ranged from 22% to 48%) in 5-caffeoylqunic acid content (the most abundant phenolic acid) in eight eggplant samples collected from eight different plants belonging to the same cultivar and grown under similar conditions. The cv. Millionaire showed a higher total phenolic content compared to the Blackbell cultivar. We did not observe significant consistent trend in the phenolic content of eggplant samples grown with organic and conventional farming practices with both eggplant cultivars. We, however, observed a strong correlation (R2 = 0.87) between total phenolic content as assayed by Folin–Ciocalteu assay and 5-caffeoylqunic acid, a major phenolic acid in eggplant extract. This study concludes that multiple repetitive analyses of plant products collected from different plants grown over various time periods (seasons) at different locations should always be carried to unambiguously prove the impact of growing conditions on phenolic content or antioxidant activity.