Effect of drying methods on colour stability, lycopene retention, total phenolic content, total flavonoid content, and antioxidant activity of dried tomatoes under accelerated storage conditions

Tomatoes (Solanum lycopersicum L.) are known to be rich in compounds that are bioactive, particularly lycopene and phenolic antioxidants, though postharvest processing often diminishes their nutritional and visual quality. This study evaluated four drying methods, conventional drying (Conv_Ctrl), greenhouse solar drying (GrnHSe_D), optimised greenhouse solar drying (Optm-GrnHSe_D), and traditional sun drying (TradSun_D), for their effects on quality retention during 35 days of accelerated storage (37 °C, 75% RH). Total colour difference (ΔE), chromaticity (C) and colour parameters (L∗, a∗, and b∗) were monitored alongside quantitative analyses of antioxidant activity (ABTS and DPPH assays), total phenolic content (TPC) and total flavonoid content (TFC) at 7, 21, and 35 days, while lycopene content (LC) was assessed only on day 35 across all drying treatments. Results demonstrated that Optm-GrnHSe_D effectively preserved quality attributes, showing better colour retention (ΔE = 4.11 versus 7.96 in TradSun_D), higher LC (15.52 mg/100 g wb) and greater antioxidant capacity (82.4% wb DPPH inhibition at day 7). Chromaticity analysis confirmed progressive pigment degradation in TradSun_D (0.71 at week 5) compared to more stable retention in Optm-GrnHSe_D (0.08) and Conv_Ctrl (0.06). Strong correlations emerged between LC and effects of antioxidative capacity (DPPH was r = 0.999; ABTS was r = 0.987), while phenolics, including flavonoids, showed excellent stability in controlled drying methods (TPC7-TPC21: r = 0.999; TFC7-TFC21: r = 0.989) versus significant losses in TradSun_D (TPC35: 0.38 mg/g wb; TFC35: 0.18 mg/g wb). The optimised greenhouse solar drying method proved particularly effective at mitigating thermal degradation, offering an energy-efficient alternative that maintains nutritional quality. The importance of using a specific method while drying was highlighted, with a suggestion for future research in hybrid drying technologies.