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This is a Quantitative Study study.

September 26, 2025Open Access

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

ONOwenkosi Kuriakos NyawoUniversity of Johannesburg TMTumisi Beiri Jeremiah MolelekoaUniversity of Johannesburg LSLaura Suzanne Da SilvaTshwane University of Technology

Key Points

The optimized greenhouse solar drying method demonstrated superior retention of nutrients and antioxidants in dried tomatoes.
Lycopene content was highest in tomatoes dried using optimized greenhouse solar methods, recording 15.52 mg/100 g.
Traditional sun drying led to significant losses in phenolic and flavonoid contents, with TPC35 at 0.38 mg/g.
The study suggests that controlled drying methods effectively mitigate thermal degradation and enhance overall quality.

Abstract

Abstract 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 (ConvCtrl), greenhouse solar drying (GrnHSeD), optimized greenhouse solar drying (Optm-GrnHSeD) and traditional sun drying (TradSunD), 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 was assessed only on day 35 across all drying treatments. Results demonstrated that Optm-GrnHSeD effectively preserved quality attributes, showing better colour retention (ΔE = 4. 11 versus 7. 96 in TradSunD), higher lycopene content (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 TradSunD (0. 71 at week 5) compared to more stable retention in Optm-GrnHSeD (0. 08) and ConvCtrl (0. 06). Strong correlations emerged between lycopene content 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 TradSunD (TPC35: 0. 38 mg/g wb; TFC35: 0. 18 mg/g wb). The optimized 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 method while drying was highlighted, while suggesting future research in hybrid drying technologies.

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