Atmospheric cold plasma (CP) treatment as an alternative non-thermal fruit surface decontamination.

This project aimed to evaluate the efficacy of both direct and in-package cold plasma (CP) treatments on the decontaminating of surface microbes and inactivation and control of Botrytis cinerea and Monilinia laxa on nectarine and plum fruits. The rationale was to develop a sustainable, non-chemical, residue-free method for reducing postharvest fungal decay and extending shelf life. Cold plasma offers a promising alternative to conventional fungicides, aligning with global demands for safer, environmentally friendly postharvest treatments.

Direct cold plasma treatments were applied at varying intensities (0–85 kV) for 2 and 5 minutes for (In-vivo) and 80 kV for 0-10 min for in-vitro studies. Curative efficacy of CP was then investigated against B. cinerea and Monilinia laxa for nectarines and plum. In-package CP treatments were conducted using perforated packaging. Microbial counts were determined using PCA and PDA media. Lesion progression, physicochemical attributes, and SEM imaging were evaluated during storage. The curative efficacy of CP was assessed for both pathogens under controlled conditions. The study included fruit (nectarines) harvested from two locations and seasons and plums harvested from one location for one season.

Exposure at High-intensity direct cold plasma (CP) treatment showed strong antimicrobial efficacy, with exposure at 80 kV for 3 min completely inhibiting Botrytis cinerea mycelial growth (in vitro) and treatments at 75–85 kV for 5 min achieving the highest in vivo microbial inactivation, including complete suppression of aerobic bacteria. However, CP at 80 kV induced fine surface porosity on nectarine fruit immediately after treatment, potentially compromising postharvest quality, whereas lower CP intensity (50 kV for 2–5 min) preserved initial visual quality. For plums, maximum decay suppression was achieved at 8 °C with CP treatments of 2–5 min, while extended exposure (10 min) promoted fungal growth, and CP followed by low-temperature storage (>2 °C) provided no additional benefits for quality or decay control. In-package CP delayed fungal growth but was less effective than direct CP due to the use of perforated packaging; nevertheless, it preserved fruit colour and firmness, reduced weight loss and prevented the surface porosity associated with direct CP. Overall, B. cinerea exhibited higher resistance to CP treatment than M. laxa.

Direct CP effectively reduces microbial loads and fungal decay in stone fruits (nectarine and plum), with efficacy dependent on plasma intensity, exposure time, pathogen susceptibility and storage temperature. While fungal elimination was not always complete, lesion development was significantly delayed. Direct CP (75–85 kV/5 min) offers strong decontamination and inactivation but risks surface damage. CP at low intensity (50 kV) maintained fruit quality. In-package CP is practical for quality retention at highest plasma intensity but limited by reactive species loss via perforations. Optimal balance (50 kV/5 min for visual quality; 8°C storage) recommended for shelf-life extension.

Direct cold plasma (CP) treatment at high intensity (75–85 kV for 5 min) is effective for critical decontamination, as demonstrated by in vitro results. However, in vivo  assessments indicate that such conditions can induce surface porosity that lead to accelerated quality deterioration during storage. Lower-intensity CP treatment (50 kV) can mitigate these detrimental quality effects but at the expense of reduced microbial inactivation efficiency.

In-package CP treatment offers an alternative strategy to overcome the quality limitations associated with high-intensity direct CP by preserving fruit integrity while maintaining antimicrobial efficacy. However, vacuum CP systems are unsuitable for this application, as they do not permit a fully sealed package which is an essential requirement for retaining reactive species and achieving maximum inactivation. Consequently, alternative plasma technologies, such as dielectric barrier discharge (DBD) systems can be explored for more suitable  in-package industrial implementation.