Nanoemulsion of wild ginger (Zingiber zerumbet(L.) Smith) essential oil for postharvest management in Banana

Abstract

Essential oils (EOs) are potent natural antimicrobials and antioxidants, but their practical application in food preservation is often limited by high volatility, poor water solubility, and susceptibility to degradation. Wild ginger (Zingiber zerumbet (L.) Smith), a rich source of bioactive EO, presents a promising yet underutilised natural resource. Simultaneously, climacteric fruits such as banana (Musa spp. cv. Nendran) suffer from rapid ripening and significant postharvest losses. Nanoemulsification of EO is an advanced strategy to enhance stability, dispersibility, and controlled release, thereby increasing efficacy. The present study was carried out at the Department of Postharvest Management, College of Agriculture, Vellanikkara, during 2023-2025, aimed to chemically profile Z. zerumbet EO, optimise a stable sodium alginate-based essential oil nanoemulsion (EONE) using ultrasonication, and evaluate its efficacy as a postharvest coating to extend the shelf life of banana cv. Nendran. In the first experiment, the hydro-distilled EO from Z. zerumbet rhizomes was chemically profiled and compared with cultivated ginger (Zingiber officinale cv. Varada). Z. zerumbet produced a significantly higher EO yield (3.3 ± 0.18%) than Z. officinale (1.6 ± 0.07%). and demonstrated significantly stronger antioxidant activity in the DPPH assay (IC50 value of 1476 ± 103.62 μg/mL compared to 5093.33 ± 166.57 μg/mL). Gas Chromatography-Mass Spectrometry (GC-MS) analysis identified 61 compounds in Z. zerumbet EO, with the major constituents being Zerumbone (32.46%), Camphene (14.88%), α-Humulene (6.49%), and Camphor (6.69%). In contrast, the analysis of Z. officinale EO identified 97 compounds, with a distinctly different profile, predominantly composed of Zingiberene (22.81%), β-Sesquiphellandrene (11.69%), Camphene (7.30%), and α-Curcumene (6.47%). Following the chemical screening, the Z. zerumbet EO was encapsulated in a sodium alginate-based nanoemulsion to develop a stable delivery system. The synthesis was optimised using a Response Surface Methodology (RSM) approach to evaluate the effects of three independent variables: essential oil concentration (1-5%), surfactant concentration (1-5%), and sonication time (5-15%). The optimisation was based on achieving the minimum particle size and polydispersity index (PDI). The experimental runs yielded particle sizes ranging from a highly desirable 10.6 nm to a non-nano 4339 nm. Statistical analysis revealed that surfactant concentration was the most significant factor (p=0.0091) influencing the PDI. The optimal formulation, derived from Run 15, was identified as 1% essential oil, 5% surfactant, and a sonication time of 10 minutes. This combination successfully produced a stable, translucent NE with the smallest mean particle size (10.76 nm) and an excellent, low PDI of 0.1845, indicating a uniform and monodisperse system suitable for application. In the final experiment, the optimised EONE (T1) was applied as a postharvest coating to banana cv. Nendran and compared with a coarse emulsion (EOE, T2), a chemical check (0.1% Carbendazim, T3), and an untreated control (T4), all stored at ambient conditions. The untreated control fruits ripened and perished by day 11, whereas the EONE maintained marketability up to 14 days. T1 demonstrated a delayed ripening process (maintaining a 'Light Yellowish Green' stage until day 12, T4 turned 'Vivid Yellow' by day 5). T1-treated fruits showed the lowest physiological loss in weight (10.18 ± 0.90%) and total soluble solids (25.35 °Brix) by day 12. In contrast, all other treatments either perished or had TSS levels over 30 °Brix. The EONE effectively reduced disease incidence, maintaining a disease severity index (DSI) of 10.62 % on day 10 compared with 43.94 % (T2) and 62.71 % (T4). In sensory evaluations on the final day, T1 received the highest total score (56.90), with superior texture (8.80) and taste (8.50), while the control (24.50) was rated unacceptable. This study demonstrated that an optimised sodium alginate-based nanoemulsion of Z. zerumbet EO is a highly effective postharvest treatment. It successfully extended the shelf life of bananas, preserved the fruit's physiological and biochemical quality by delaying ripening, and reducing water loss. This research offers a viable and effective natural alternative to synthetic preservatives for mitigating postharvest losses in bananas