Foliar-applied humic acid modulates antioxidant and mineral profiles in tomato fruit across maturity stages

Abstract

Berry quality can further be modulated by applying foliar biostimulants to cherry tomatoes depending on their maturity stage. This study aimed to evaluate the effects of foliar application of humic acid (HA) on berry quality at different maturity stages. Humic acid was applied at concentrations of 0, 25, 50, and 75 mg L-¹ during the vegetative, flowering, and fruit-setting phases. Berries were harvested at four distinct maturity stages: mature green (MG), breaker (BK), pink (PK), and red (RD) stages. HA, particularly HA75, significantly enhanced berry quality when harvested at the red stage and exhibited better antioxidant activity due to elevated levels of vitamin C (44.20 mg 100 g-1 FW), lycopene (0.25 mg 100 g-1 FW), and β-carotene (27.58 mg 100 g-1 FW). It also had higher total soluble solids (6.17 °Brix) and pH (4.07) values. The reducing sugar content increased from 0.84% in mature green berries to 1.39% in red berries with the application of HA0 and HA75, respectively. The shelf-life of berries was extended from 13.28 days (HA0) to 15.58 days (HA75) at the green mature stage. Dry matter content peaked at 8.82% in HA75-treated mature green berries, whereas moisture content was highest (94.19%) in untreated (HA0) red berries. Conversely, at the red stage, HA50 and HA75 treatments resulted in the highest redness (a* values of 13.21 and 10.20, respectively), compared to 12.60 for the control (HA0). Lightness (L*) was highest in mature green berries treated with HA50 (61.43), indicating brighter fruit surfaces, whereas red berries showed lower L* values (49.80-52.70), consistent with ripening progression. Mineral uptake also improved, with Mg (2.39%), P (0.71%), and Fe (213.54 ppm) being the highest in HA75-treated red berries. These findings suggest that while humic acid can enhance certain quality traits, the maturity stage remains the dominant factor influencing berry quality traits