Improving the Postharvest Storage and Quality of Tomatoes (Solanum lycopersicum L.) Using Biochar Derived from Spent Tea Leaves

Ethylene accumulation accelerates the ripening of climacteric fruits and may impair their postharvest quality. This study evaluated biochar produced from spent tea leaves and enclosed in cellulose sachets as a material for reducing ethylene concentration and preserving tomato quality during storage. The biochar was produced by pyrolyzing spent black tea leaves at 400 °C for 10 min. Tomatoes were stored for 18 days at 21 °C in sealed glass chambers containing sachets with 1, 2, 3, 4, 5, 7.5, or 10 g of biochar, with a treatment without biochar serving as the control. After 6, 12, and 18 days, ethylene concentration, microbiological quality, and selected physicochemical and antioxidant properties were evaluated. Biochar reduced ethylene accumulation in a mass-dependent manner, with the most pronounced effects generally observed in the 5–10 g range. The 10 g treatment reduced ethylene concentration by 41.1%, 37.8%, and 40.3% relative to the control after 6, 12, and 18 days, respectively. The lowest counts of aerobic mesophilic microorganisms, yeasts, and molds were generally observed in the 7.5 and 10 g treatments. The application of at least 5 g of biochar most effectively limited firmness loss; after 18 days, firmness ranged from 1.77 to 1.80 kgf in the 5–10 g treatments, compared with 1.00 kgf in the control. Higher biochar masses also favored the retention of titratable acidity, total phenolic content, and antioxidant activity measured using the ABTS and FRAP assays. Overall, the beneficial effects on postharvest storage conditions and tomato quality became more evident with increasing biochar mass, particularly between 5 and 10 g. Sachets containing 7.5–10 g of spent-tea-leaf biochar showed the greatest potential as a simple passive system for controlling ethylene and preserving tomato quality. This approach combines waste valorization with the potential reduction in postharvest losses, supporting circular economy principles and Sustainable Development Goal 12 (SDG 12).