Low-wetting ultrasonic micro-mist as a postharvest treatment for sliced mushrooms (Agaricus bisporus)

Ultrasonic nebulization generates a micro-mist that rapidly wets surfaces with minimal liquid load, making it attractive as a rinse-free postharvest step for delicate, cut produce. This study evaluated an ultrasonic nebulization treatment for sliced mushrooms using 5 ppm of chlorine dioxide (ClO₂), 80 ppm of peracetic acid (PAA), water, and a non-nebulized control. Slices were treated in a sealed chamber for a total of 2 min (two cycles of 1-min ON/2-min OFF) using nebulizers with an ultrafine spray aperture (~5 μm) and stored at 5 °C and 85% RH for 11 days. Weight loss, firmness, color, browning index, overall appearance, pH, total phenolics, antioxidant capacity, and microbiology counts (total aerobic mesophiles, yeasts, and molds) were monitored every 3-4 days. Weight loss was higher for PAA and water-treated slices (p<0.05). No significant differences were detected among treatments for firmness, browning index, color (chroma), or overall appearance across storage (p<0.05). PAA showed the highest pH at the end of storage. Total phenolics and antioxidant capacity were higher in ClO₂-treated slices throughout storage, except on day 0, when PAA showed the greatest values (p < 0.05). Microbiological analyses showed modest but significant decreases in total aerobic counts for both ClO₂ and PAA, as well as for yeasts and molds with ClO₂, compared to the control (p < 0.05). Overall, ultrasonic nebulization with ClO₂ or PAA showed potential to reduce microbial load while maintaining sliced-mushroom quality, with ClO₂ supporting higher total phenolics and antioxidant capacity. Future work should optimize dose and duty cycle to balance antimicrobial effect with preservation of antioxidants.