Postharvest quality and fungicide residue quantification (LC-MS) in ‘Gala’ apples treated with zein-based nanocapsules containing essential oils and Bacillus spp. based biofungicides

Abstract

The apple (Malus domestica Borkh) is subject to postharvest losses. Apple scab (Venturia inaequalis) throughout crop cycle can interfere with postharvest fruit quality, while chemical control with fungicides compromise food safety. This study aimed to evaluate effect of essential oil (EO) nanocapsules and Bacillus spp.-based biofungicides on apple postharvest quality and to quantify fungicide residues. Nanocapsules showed mean sizes of 192.6 ± 3.1 nm (NANO-EOO) and 210.13 ± 2.8 nm (NANO-EOE), with homogeneous distribution (PDI ≈ 0.120 ± 0.04) and high electrophoretic stability, indicated by zeta potential values of 40.5 ± 0.8 and 38.2 ± 2.0. Field treatments included Nano-EOO, Nano-EOE, Bacillus amyloliquefaciens (BAM1 and BAM2), Bacillus subtilis (BSU), and chemical control (Control-NT). After six sprayings, fruits were evaluated for physicochemical and biochemical parameters and fungicide residues. No statistical differences were observed in fruit weight and diameter; however, Nano-EOO showed highest averages (44.84 cm; 391.75 g). Nano-EOE resulted in greater pulp firmness and lower starch content. Epidermis coloration varied among treatments (L* ≈ 57.3/∼30.9), with higher yellow intensity in Nano-EOO (b* ≈ 36.5). BSU showed lower phenolic content (0.05095 mg/g) and antioxidant activity (∼24.98%), while BAM1 and BAM2 promoted higher values, especially BAM1 (0.17082 mg/g; 75.2%). Soluble solids and titratable acidity didn't differ among treatments, while Nano-EOE reduced starch index (∼8; p < 0.01–0.001), indicating more advanced maturation. LC-MS analyses confirmed absence of detectable residues of difenoconazole (<5 ppb) and mancozeb. These results demonstrate that alternative formulations maintain fruit quality, ensure food safety, and represent alternatives to synthetic fungicides.