Efficacy of black soldier fly-derived chitosan coatings in managing post-harvest decay of blueberries

Abstract

Post-harvest decay and moisture loss reduce the marketable life of blueberries and can cause substantial losses where fruit are held under ambient conditions. This study evaluated black soldier fly-derived chitosan coatings for managing post-harvest deterioration of 'Azra Blue' blueberries. A Completely Randomised Design was used with four treatments: distilled-water control (T1), 0.5% chitosan (T2), 1.0% chitosan (T3) and 1.5% chitosan (T4). Each treatment comprised three Petri-dish replicates containing nine berries, giving 108 fruits in total. Following artificial inoculation with grey-mould propagules collected from symptomatic blueberry fruit, the fruits were coated and stored under ambient winter laboratory conditions in Bindura for 15 days. Weight loss and berry diameter were assessed on Days 0, 5, 10 and 15, while disease incidence and severity were assessed on Days 5, 10 and 15. Fruit-juice pH was estimated descriptively using universal indicator strips. One-way analysis of variance and Fisher's Least Significant Difference test were applied at P ≤ 0.05. Weight loss increased with storage duration but was significantly reduced by chitosan. At Day 15, the control recorded 10.70% weight loss compared with 8.23%, 6.60% and 5.40% for T2, T3 and T4, respectively. Mean berry diameter at Day 15 was lowest in the control (17.51 mm) and highest in T4 (18.53 mm). Disease incidence reached 70.4% in the control, compared with 44.4%, 37.0% and 33.3% in T2, T3 and T4. The Day 15 Disease Severity Index was 37.0% in the control and 11.1%, 10.2% and 8.3% in T2, T3 and T4. Grey mould in coated fruit generally remained localised around the stem scar, whereas the control showed more extensive sporulation. Approximate pH was 4 in the control and 3 in the coated fruit at Day 15. The findings indicate that black soldier fly-derived chitosan reduced moisture loss, maintained berry size and suppressed presumptive grey mould development, with 1.5% chitosan providing the strongest overall protection under the conditions of the study. Further validation under controlled cold-chain and commercial handling conditions is recommended.